If you have an irrigation system that currently has a pump on it, and everything has worked good right up to the point the existing pump died, then your best bet is to replace the pump with the exact same model as the old one. This is a much, much easier process than trying to find a different make or model of pump. However if the old pump wasn’t really getting the job done, or isn’t available anymore, this is a good time to reevaluate your pump needs. Perhaps there is a better pump out there for your system.
Here’s the basic procedure to follow if you’re trying to find the right pump horsepower and model for a new irrigation system. You’ll probably want to refer back to this list as you learn more. If you want to replace or add a pump for an existing irrigation system please see the article on Selecting A Replacement Pump For An Existing Irrigation System.
To figure out the distance the water will move to the side (horizontally) in the soil you can perform a simple test. Perform this test some place in or near the area you plan to irrigate. Be aware that soil types can be different just a short distance apart. I’ve seen many rural home lots where the soil on one side of the property was sandy and it was clay on the other side. For the test you need to select an area of ground about 1.5 meters (5 feet) in diameter. It works best if the test area is undisturbed soil that has not been recently dug up or tilled. The top 150mm (6 inches) of soil in your test area needs to be dry, so allow it to dry out if it is wet. Clear the area of any surface debris and smooth the soil surface if it is uneven. Push a nail or some other marker into the center of your test area to identify it. (If rain prevents the test area from drying out, try building a low berm around the uphill side of the test area to keep rain water from draining onto it. Then cover the area with a tarp when it rains. Remove the tarp as soon as the rain stops so the sun and wind can help dry the soil.)
Start with an empty 2 liter plastic drink bottle or a gallon milk jug (the size of the container is not critical.) Heat a straight pin over a flame (hold the pin with pliers so you don’t burn your fingers!) then use the pin to make a tiny pin hole in the bottom of the bottle. Put your finger over the hole in the bottle and fill the bottle with water. Now place the bottle in the middle of the test area and allow the water to flow out of the pin hole onto the soil next to the nail/marker you installed (it does not need to flow directly onto the marker, just in the general area around it.) The water will squirt out fast at first and then start to drip more slowly as the bottle empties. Once the bottle empties (it may take a couple of hours) refill it and repeat. You may refill the bottle a third time and repeat if you wish, but generally at this point more water does not make the wetted area any wider (the additional water just flows down deeper into the soil.) As the water flows from the bottle it is important that the water does not start to form a large puddle (more than 150mm or 6 inch diameter) on the soil surface. If it does start creating a large puddle remove the bottle for a while and allow some time for the water to soak into the soil. Then put the bottle back and allow more water to flow out onto the soil. Next wait at least 12 hours from the time you started the test to allow the water time to move into and through the soil. If your soil is clay you may need to wait as long as 3 days for the water to move the maximum distance. Once the wet area has stopped growing measure the size of the area that is moist. You should be able to visibly see a wet area around the marker, but since roots don’t normally grow on the soil surface you should measure the distance below the surface. Dig three or four shallow trenches about 25mm to 50mm deep (1-2 inches) starting at the marker and extending in different directions toward the edge of the test area. Measure how far from the marker the soil is moist in the bottom of each trench. Don’t be surprised if the wet area is larger below the soil surface, that is normal. Average the total lengths you measured to determine how far the water will soak sideways in your soil.
This page provides links to several “Installation Details.” These details show the installer what the finished installation should look like for various components of the irrigation system. They are essentially a statement of expected quality. Not all of these details drawings will apply to every irrigation system. Use them as a guideline.
You can modify these details as needed to fit your project. Most of these details were created for very high quality irrigation systems, and so if you are a homeowner they may in some cases be over-kill. A word of warning however. High quality, even on a residential system, is not always a bad thing! There is generally a good reason for everything that is labeled out on these details. Before changing things it is advisable to seriously consider why they are drawn as they are. For instance, many details call for the use of metal pipe above ground level. This might seem to be a waste until you consider that plastic pipe becomes extremely brittle and easily breaks in just a few years when it is exposed to sunlight! Along the same line of thought, most of these details show galvanized steel pipe when metal pipe is needed. In some cases it may be advisable to use brass or copper pipe in place of galvanized. This would be a very good idea if you have soils with a high salt content or if your sprinkler system is within a few miles of the ocean. Salt, moisture, and steel pipe do not get along very well. Have you ever noticed how corroded and rusted exposed steel surfaces are near the beach?
The rest of this page is dedicated to those of you who are considering becoming a professional irrigation system designer or installer.
In the irrigation industry these little drawings are called “installation details,” often abbreviated as simply “details.” A typical set of plans for a sprinkler system might have a dozen or so of these little Installation details included with it. I’ve seen plan sets with 100 or more installation details covering everything down to the smallest part of the system.
Designers: Show the Result, Not the Method
These drawings show the installer what type of materials to use and how they should be installed relative to each other. They do not show the contractor HOW to install them. The industry standard is that the designer never tells the contractor how to do the work, only what is expected in the finished product. If you as a designer tell the contractor how to do the installation, then you may be partly liable if someone is injured during the work. So let the contractor decide how to get it installed, you just tell him what the finished product should look like. As you look at these detail drawing you will notice they specify materials to use (types, sizes, brands, model numbers, etc.) and placement (depths and distances from other components.) They never tell the contractor “how” to do the job or the method to use to achieve that look. (ie; never say “dig a hole 24″ deep using a spade-type shovel.” That would be telling the contractor how to do the job.)
Installers: Compliance with Details is not Optional
Over the years I have encountered many inexperienced contractor/installers who for some reason thought the plans were just a technicality, a “rough guideline.” They didn’t think they needed to follow them. So they figured they could just do their own thing. If you are an installer and you are given a set of plans, you probably also signed a contract, and the fine print in that contract says you agree to install the system as shown on the plans.
If you are given a set of plans for installation and you don’t agree with something on those plans or think there is an error, ask for clarification! Never proceed with the installation if you think the designer made an error. If you do install something you know is wrong you may become liable for that error and made to fix it at your own expense! Even worse are the installers who just toss the plans out and do their own thing. If you just install the system the way you want to and ignore the plans and installation details you probably will not get paid for the work! In fact you may have to pay damages to the property owner. Most of the standard contract forms used by professionals in the landscape and irrigation industry are carefully written by attorneys based on case law. Over the course of my 35 year career I have seen dozens of contractors forced into bankruptcy and lose everything, simply because they did not follow the plans and installation details for a project. They were all offered the opportunity to correct the problems, but most simply couldn’t afford to remove it all and replace it. This is especially true of big commercial jobs like shopping centers. The developer of that shopping center doesn’t know you, is not your friend, and won’t have a second thought about taking everything you own. So if you think there is an error on a set of plans always state your concerns to whomever you are working for and ask for clarification. Don’t be the fall guy, protect yourself!
Gravity flow systems tend to have extremely low water pressure which creates problems with emitter operation and a lack of watering uniformity. The first emitter on a tube will very likely put out a lot more water in 30 minutes than the last emitter will. Standard electric actuated irrigation valves will usually not work with these systems due to the low water pressure. To automate them you usually need a more expensive motor-operated valve. Fortunately most folks using rain barrels aren’t interested in anything fancy and just turn the drip system on and off using an old fashioned hand operated valve.
If you are planning to use a rain barrel or other low-pressure gravity flow system I recommend you try the emitters commonly called “Flag” or “Take-apart” Emitters. You will find more information on these on the emitters page.
Elevate Your Rain Barrel!
Unless the water source (rain barrel in most cases) is elevated a meter (3 feet) or so above the emitters, even the low-pressure flag emitters may work poorly or not work at all. A barrel set on the ground often works well when the barrel is full of water and then stops working as the water level drops. The solution to this problem is to elevate the barrel on a stand. To get really good water distribution uniformity it is often necessary for the water source (barrel) to be 10,5 meters (yes, that’s 35 feet) above the emitters. Height creates water pressure, and the pressure is necessary for good uniformity. With that said, it is my experience that most people who use water barrels are more interested in having a primitive or “green” irrigation system than they are in having an efficient one, and are sufficiently satisfied with the uneven water distribution. Keep your drip tubes as short as possible. I strongly recommend that you mock-up a test system using your barrel, a valve, filter and at least one row of tube with emitters and test how well it works. You can then make modifications as needed to your design before investing too much money on materials you might not need. Remember the key to success if you have problems is almost always to raise the height of the barrel. A lot of people give up without trying that simple solution!
Grab a piece of string about 6″(152mm) long. Strip away any insulation so you can get at the pipe and wrap the string around it. Measure how many inches of string it takes to go around the pipe once. This is the circumference of the pipe (yikes, bad memories of high school geometry!). Using the circumference we can calculate the diameter of the pipe. But school’s out so let’s forget about doing geometry calculations! Based on the string length use the table below to find your pipe size.
For Copper or PEX Pipe
2.75″ (70mm) = 3/4″ pipe
3.53″ (90mm) = 1″ pipe
4.32″ (110mm) = 1 1/4″ pipe
5.10″ (130mm) = 1 1/2″ pipe
For Steel Pipe or PVC Plastic Pipe
3.25″ (83mm) = 3/4″ pipe
4.00″(102mm) = 1″ pipe
5.00″(127mm) = 1 1/4″ pipe
6.00″(152mm) = 1 1/2″ pipe
For Flexible Polyethylene Pipe
2.96-3.33″ (75-85mm) = 3/4″ pipe
3.74-4.24″ (95-108mm) = 1″ pipe
4.90-5.57″ (124-141mm) = 1 1/4″ pipe
5.70-6.28″ (145-160mm) = 1 1/2″ pipe
Your string length will probably not be exactly the same as the lengths in the chart. Measurements vary a little, depending on how much the string stretches, dirt on the pipe, manufacturing tolerance of the pipe, how accurate you are at measuring, etc.
There are many different kinds of valves available. Most drip irrigation systems will need at least two different types; an emergency shut-off valve and a control valve.
Emergency Shut-Off Valve
An emergency shut-off valve should be installed at the closest point possible to your water source, that is, the location where you tap in for the irrigation system. Without this valve you will need to shut-off the water to the entire house if you have an irrigation breakdown and need to work on the mainline or irrigation valves. The most commonly used valves for this purpose are “gate valves” because they are inexpensive. Unfortunately the cheap gate valves you’re likely to use also tend to wear out quickly and start leaking. While a gate valve will get you by, I recommend that you use a “ball valve”, “disk valve”, or “butterfly valve”. These may cost a bit more (prices are becoming more reasonable as ball valves slowly are replacing gate valves for plumbing.) Ball valves are the least expensive of these and are much more reliable and will last several times longer than a gate valve. So if you pay twice as much for a ball valve it’s probably still the best deal! If you do use a gate valve make sure that it is a good quality one. There’s nothing worse than trying to work on a irrigation system when you can’t shut off the water completely. For some very small drip systems an emergency shut-off valve is simply not cost effective. For example; a manually operated drip system where an existing faucet or hose bib is used to turn the system on and off.
Zone Control Valves
Zone Control valves are the valves that turn on and off the water to the drip tubes. Often these are automated valves that are turned on and off by a irrigation controller/timer. For a small drip system there may be only one zone control valve. Bigger systems may have several zone control valves, for example they may have one the turns on the water to the front yard, another for the side yard, one for the vegetable garden and a final one for the back yard. There are two basic styles of zone control valves to choose from. Take a look at the image below, descriptions follow.
Standard Globe Valve:
Glove valves are available in just about any size. They are often installed underground in a box or vault. Since a globe valve doesn’t incorporate a backflow preventer you must provide one separately. See the section on backflow preventers. The globe style valve is the most commonly used valve on large commercial drip systems.
Available only in 20mm (3/4 inch) and 25mm (1 inch) sizes. This is my recommendation for most homeowners. The anti-siphon valve incorporates a backflow preventer into the valve. This saves a considerable amount of money, as backflow preventers are very expensive. The anti-siphon valve MUST be installed above ground and MUST be at least 150mm (6″) higher than the highest drip emitter. This may prove a problem for some locations, since you would likely have to put the valves at the highest point in the yard. I have seen a anti-siphon valve installed on top of trellis in order to get it above the emitters for hanging baskets. On a slope the simplest solution is to run a mainline up the slope to the anti-siphon valve installed at the top of the slope. From there pipes run down to the emitters.
Indexing Valves (standard and anti-siphon):
Indexing valves are a single valve unit that controls several valve zones. The index valve has a water inlet and several water outlets. When the valve receives a signal from the control unit it opens the first water outlet, at the next signal it switches from the first to the second outlet. At each signal it switches to the next outlet until it gets back to the first outlet, at which point it shuts off. Indexing valves require a special controller to operate them. Indexing valves are usually available in models with or without a built in anti-siphon device. So an indexing valve may be also an anti-siphon valve. The anti-siphon indexing valve MUST be installed above ground and MUST be at least 150mm (6″) higher than the highest drip emitter. Indexing valves have never been widely popular and are generally only available in localized regions where a nearby manufacturer has heavily promoted them. Perhaps the best know indexing valve is made by the K-Rain company, they are popular in Florida where K-Rain is located.
The control valves may be manually operated or they can be remotely controlled. Manual control is simple, the valve has a handle you use to turn it on. Remote control valves are either electric or hydraulic, but almost everyone uses electric solenoid type valves. The valves are turned on and off by a timer called an “irrigation controller” or often just called a “controller”. Anti-siphon, globe, and angle valves are all available as automatic valves. Most controllers and valves sold today are standardized, you don’t need to use the same brand of controller and valve. The standard is a normally closed valve that uses 24 volt alternating current to actuate the valve. When 24 volts of current is applied to the valve solenoid wires the valve opens, when the voltage is turned off the valve slowly closes. This way the valve will close during a power failure or if a wire breaks. There are some exceptions to this standard operation method. To save power, controllers that run on batteries or solar power often use a special type of solenoid on the valves called a “latching solenoid”. Latching solenoids work like a toggle switch, when a short burst of power is detected the valve switches open (if it was closed) or closed (if it was already open). Generally if latching solenoids are required there will be a warning and instructions on the controller. If the controller doesn’t plug into a power source, chances are it uses latching solenoids. There are a few specialty controllers and valves that use their own proprietory system and are not compatible with either the standard or latching solenoids, but these are rare and seldom used by homeowners. The most common are Indexing Valves (see above). Another common one is a small solar-powered controller and custom valve solenoid combination sold under the brand name LEIT®. While a little beyond the budget of most homeowners, LEIT controllers can operate on very low levels of light, they claim moonlight is sufficient. (If you see something that looks like a parking meter installed in the middle of a landscaped road median island, you’ve spotted a LEIT controller. They are very popular with highway departments.)
Valve Body Materials:
Valves are available with either brass or plastic bodies. Most valves today are plastic, but brass is still widely available and preferred by some pros, especially when high water pressure is present. There is no doubt that a brass valve will last longer if installed in the sunlight. From an operational point of view, both are reliable, especially for automatic systems. For manual valves my experience is that brass will last much longer. For automatic control valves I almost always use plastic, my experience is that when buried or protected from sunlight it holds up as well as brass and is less expensive. If you use plastic valves above ground you may wish to consider building a cover for them to protect them from sunlight, which can destroy the plastic over time. My experience is that even when made using UV resistant plastic, the plastic valves will start to break down after a few years in the sunlight. Most residential oriented plastic valves are made using PVC or ABS plastic. A fiberglass reinforced nylon material is often used for the bodies of more expensive valves aimed at the commercial, parks and golf course markets.
Note: You will notice when I give the English unit equivalents of the metric they are not exact. This is because I am fudging the values to give you the values most commonly used in the industry. So while 1 meter is 39.37 inches, if I am using the distance in reference to emitter spacing, I may convert it to 36 inches to reflect the common spacing you will find when shopping for drip products in the USA.
Water, Soil, and Plants
You’re out in the desert (on a horse with no name?) and you’re really hot and thirsty. So you open your canteen and pour all the water over your head. It feels really great, but you’re still thirsty. Why? Because you don’t drink water through your hair follicles! As most people are aware, most plants “drink” through their roots. But not all of the roots are for drinking. The roots that most plants use for drinking (and eating too) are found in the top 15 cm (6 inches) of the soil. (I often see water conservation articles that say the roots in the top 45 cm uptake water, but in my practical experience most common garden plants seem to have great difficulty utilizing water deeper than 15 cm. Desert plants and chaparral plants are an exception, they do tap into water far below the soil surface.) The deeper roots are primarily for holding the plant in place. Watering these lower roots is a waste of water, just as pouring water over a thirsty man’s head is a waste of water!
Now lets take that same thirsty man and give him a large cup of water. But we’ll force him to drink it through one of those tiny plastic straws used to stir coffee. That doesn’t help much either, does it? The point is that, like the man, the plant can only drink water if it is applied in the proper place, in the proper amount. The plant can only take up a limited amount of water through a single root, so we have to get the water to as many “feeder roots” (the roots the plant uses to obtain water and nutrients) as possible or the plant won’t be able to get enough water. How do we do this? Stupid question?
As a general rule, the feeder roots of most common garden plants are primarily located in the top 15 cm (6 inches) of soil throughout the area called the drip zone. The “drip zone” is the area of soil located directly under the leaves of the plant. If you draw a circle around the plant on the ground at the outer edge of the plant’s leaves, the area within that circle is the drip zone. (The line at the edge of the leaves is called the “drip line“.) So we need to concentrate on watering that area under the leaves in order to make the most efficient use of our water. That also makes for a healthy plant. Again, desert plants and those adapted to very dry climates have wider ranging feeder roots that allow them to adapt to a limited water supply. These plants typically only need supplemental irrigation water (often only for the first few years to get them established), so it is still OK if we only concern ourselves with irrigating the drip zone for them as well.
When we drip water onto the ground at the optimum slow rate the water will almost immediately soak into the soil. Once in the soil the water moves both downward and sideways through the soil. The water moves between the grains of soil by a combination of water pressure, gravity, and capillary action. How fast and far the water moves horizontally (sideways) from the point it is applied depends on the texture of the soil. In fine textured soils, such as clay, the water will move the farthest, but it also moves at the slowest speed. In a very “heavy” clay soil it might take days for the moisture to move the length of your arm. In “light” coarse-textured soils like sand or silt it will not move nearly as far, but it will move much faster! It might move the length of your arm in a few minutes in a silty soil.
Emitter Quantity and Spacing
The number of drip emitters needed and the distance between them is determined by the size of the drip zone and the type of soil.
Size of drip zone: If the plant has a large drip zone, like a tree, you will need more emitters than you would for a small shrub. Obviously the size of the drip zone will be smaller when the plant is young and will increase in size as the plant grows. So you need to plan for enough emitters to water the drip zone of the plant when it is mature. You can start out with just one or two emitters when the plant is a seedling, and add more emitters as the plant grows. Just be sure to plan enough water capacity in the system to supply those future emitters. So how do you figure out what size the drip zone of the mature plant will be? Just type the name of almost any plant into an Internet search engine and you will find a number of websites that will tell you what the expected diameter of that species will be when mature.
Soil type: In sandy soil your emitters will need to be closer together because the water does not move as far horizontally in a sandy soil. In a clay soil, where the water moves farther sideways, the emitters may be farther apart. Unfortunately determining what type of soil you have, and translating that into a spacing for your emitters, is difficult for the average person. Most people can’t really tell if a soil is silt or clay simply by looking at it. Even after numerous college courses in soil science and many years of experience I still get fooled now and then by a soil that doesn’t test out as I think it will. Embarrassingly, my own yard is an example of one I mis-guessed on! There are a couple of quick visual tests. One is that clay soil often cracks and splits when it dries. Another test is to take a handful of wet soil and ball it up in your hand, if it will not hold together well in a ball it is sandy or silty. Clay soil feels like… well, surely you’ve made something out of modeling clay at some point in your life and know what it feels like! It’s sticky and pliable. But the best method to find out our emitter spacing is to actually test the water movement in the soil. So the link below will provide you with instructions for a simple method of testing water movement. It involves consuming 2 liters of your favorite drink, so it can’t be too bad!
Why not just use an emitter with a higher flow rate for larger plants? This is a common misconception. The reason using a higher flow rate emitter doesn’t work is that the higher flow emitter does not wet more feeder root area. The additional water just goes down deeper into the soil or runs off on the surface, and the extra water is useless to the plant and wasted. So a larger emitter is of no help at all to a larger plant as it does not wet any more of the feeder root soil area. Going back to our thirsty man illustration, a larger emitter would be like pouring a large pitcher of water in our thirsty man’s mouth all at once. He could manage to swallow a cup or so of the water, but the rest would just spill out onto the floor. So all the emitters on your drip system should have the same flow rate. The exception: Yep, there often is one! The exception is when watering potted plants. Each potted plant may have a different size pot, a different type of soil in it, a different type of plant, and each pot may have a different sun exposure that causes the soil in the pot to dry faster. For these reasons there will be major changes in water needs between pots. When watering pots I like to use the emitters that have an adjustable flow. That way I can adjust the emitter in each pot to get the right flow rate for that specific pot.
Once you know how far the water will soak horizontally in the soil you can determine an optimal emitter spacing. Just multiple the distance the water moved by 1.9 to get the spacing distance. Using 1.9 rather than 2 allows a slight overlap of the wet areas. So if you find the water moves 525mm in the soil you would multiply 525 x 1.9 to give a optimal spacing of 1000mm or 1 meter (36 inches).
If you didn’t test the actual soil you can estimate the spacing based on the soil type.
Typical spacing of 4 lph (1 gph) emitters:
Coarse soil (sand): 60cm (24 inches)
Medium soil: 1.0m (36 inches)
Fine soil (clay): 1.3m (48 inches)
Typical spacing of 2 lph (0.5 gph) emitters:
Coarse soil (sand): 30cm (12 inches)
Medium soil: 60cm (24 inches)
Fine soil (clay): 1.0m (36 inches)
Watering Large Landscape Trees
It is pretty obvious that due to the huge diameter of a large shade tree it would take a lot of emitters to fully water the area within the tree’s drip zone. Fortunately some things help you out here. The first is that most large trees have aggressive root systems that are able to seek out water from deeper below ground and beyond the drip zone. This means that for a mature tree you can often put emitters a bit farther apart and you can even leave a few small areas of the drip zone dry. (There are always exceptions to the rules. Water loving trees like willows and cypress are going to want all the emitters and water you are willing to give them. Hopefully these water-loving trees are planted near a natural water source that they can grow roots into, like a creek or pond.) Another factor in tree irrigation is that most landscape trees are not planted alone. Typically a tree will have a lawn under part of it’s canopy, or perhaps a combination of ground cover and shrubs. Remember we are discussing large, established trees. If you are planting a new container or bareroot tree you will want to place at least two emitters per tree, one on each side of the rootball. Most newly planted trees need lots of water to get established and grow.
My design approach to drip irrigation for trees is to start by selecting the emitter locations for shrubs and groundcover as if there were not any trees. Then I add an emitter (or two) next to the rootball of each NEW tree to be planted, as well as any young existing trees. Finally, I look at both existing and future tree locations to see if there are any large unirrigated areas left under the tree canopy. Then I add emitters for those dry areas if I think they are needed. (You can look up the tree on-line to see what the water requirements are.) If I don’t think more emitters will be needed I still leave a little extra capacity in the design so I can add them later. That’s an advantage of drip irrigation; it is relatively easy to come back and add more emitters if it seems like the tree is in need of more water.
Native trees: Some established mature trees should not be irrigated. This is particularly true of some native species, especially oak trees. Regular irrigation of these trees can cause diseases that will damage or kill the tree. As a general rule if a tree is surviving well without any irrigation, it is best to not put any irrigation within the drip zone of that tree. If you are planting a new tree you may install irrigation under it in most cases. It is only mature, established trees, that have been living without irrigation for years, that have a problem with irrigation. Like a lot of older people, many old trees don’t like change! If you need to plant something under an existing native tree, most experts suggest that you plant shrubs or groundcover that can survive without any regular irrigation. Some careful hand-watering of the new plants to get them established after planting is usually OK, just keep it as minimal as possible.
Hedges, Hedge-Rows and Wind Breaks
Hedges, hedge-rows and wind breaks consist of plants placed tightly together in a row for various purposes. They are typically watered using dripperline or regular drip tube with evenly spaced emitters, similar to the description for agricultural drip systems below. Read the section below on Agricultural Drip Systems for more details. Avoid using the disposable laser-tube and drip-tape products unless you plan for the irrigation to be temporary.
Agricultural Drip Systems
In an agricultural situation most of the same rules for spacing emitters apply. The primary difference is that plants in an agricultural setting tend to be planted in rows. This means the emitters are most often placed in rows as well, and most often dripperline (also called dripline) is used. Dripperline is drip tubing with built-in emitters evenly spaced along the tubing. The advantages of dripperline are: it is easier and faster to install, the emitters are typically molded on the inside of the tube so they are less likely to be broken by field workers, and finally it is easier to move the tubes to allow the soil to be tilled, or to allow harvesting of the crop.
When watered with dripperline the roots of larger crops, such as vineyards and trees, will tend to grow in a row, following the wet soil along the length of the dripperline. This is not a problem, as in agriculture the plants are often pruned or trained into hedge-rows. So both the foliage and the irrigated roots are growing in a row.
Row Crops: For row crops emitters spaced at 30cm (12 inches) along the tube are most often used. Typically large spreading row crops (such as cucumbers and melons) use a single tube per row of plants. Most smaller row crops (strawberries, broccoli, etc.) use a wide berm with one tube down the center between two rows of plants. With row crops a lower cost disposable laser-tube or drip-tape is often used, this disposable tube/tape is intended to only last for one or two growing seasons. The disposable tube/tape is buried 75-150mm (3 to 6 inches) below ground and then is pulled up after harvest and is (hopefully) sent to a recycler. A careful gardener may get several seasons of use out of these tapes before they fill with roots and plug up. (Make sure you run the water at least weekly to help keep out roots.) For most home gardens I recommend using standard poly dripperlines, with built-in emitters spaced 30cm (12 inches) apart. This heavier poly tubing will last several years. Because the emitters are built into the tube, the tubing can be easily rolled up and stored between seasons. If you try to roll up tube with the punch-in emitters installed on it my experience is that a lot of the emitters will get broken off. I think you will find the heavier poly dripperline tube is also much more durable than the “drip tapes” which is helpful in home gardens where it is more likely to get stepped on and nicked by shovels and weeding tools.
Vineyards and Orchards: For vineyards a single dripperline is often hung above ground on the lowest vine wire. With tree crops typically two dripperlines are used, one running on each side of the row of trees, with the tubes about 1m to 1.5m apart (3-5 feet.) For larger trees like walnuts 3 or 4 rows of tubes may be used. Agricultural dripperline for vines and trees typically have emitters spaced 60cm (24 inches) apart on the tube. Remember that there is often a trade-off between water application and crop production. While using only 2 rows of tubes for trees, rather than 3-4 rows, may save money and produce a nice-looking tree, it might also cause a significant drop in crop production.
Read the Agricultural Drip Systems section above as gardens are similar. For vegetable gardens I recommend using a good dripperline with emitters spaced at 30cm (12 inches) and not buried. Connect them together using garden thread style hose couplers, or with garden hose quick connect couplers so they can be easily disassembled and removed. Use stakes to hold the dripperline in place. Top quality dripperline will last for many years and is less likely to be accidentally damaged than the disposable tapes/tubes.
Often home landscapes will have potted plants. Potted plants are where I break a lot of the rules I’ve previously given you. As noted above in the Emitter Quantity & Spacing section I like to use adjustable flow emitters for plants in pots. I also use the small diameter distribution or “spaghetti” tubing from my larger drip tube up to the emitter in the pot. The small tubing is much less ugly. I try to hide it as much as possible. A metal stake is used to hold the emitter in the pot. Do not try to put more than 2 emitters on a single length of the small distribution tubing. The small tube size restricts the flow and 2 emitters is about the maximum you can use. So a typical drip system for pots would consist of a 16mm (1/2″) tube running along the ground between the pots, a 6mm (1/4″) distribution tube from the larger tube up into the pot, and an adjustable flow emitter staked in the pot.
Emitters are classified into groups based on how their design type and the method they use to regulate pressure. You can create a very simple emitter by drilling a very small hole in a pipe. However, a hole alone does not work well. Unless the hole is extremely small, the water tends to forcefully shoot out of it like a tiny fire nozzle and way too much water will come out. More importantly, there is little uniformity of flow when using a simple hole. If you have a long pipe with holes drilled in it the holes on the end nearest the water source will have a large water flow from them, while those at the far end will have a very small flow.
Since using a simple hole in a pipe does not work very well, the early pioneers of drip irrigation started playing around with mechanical devices that would better regulate the flow. These devices have been given the name “emitters” (or sometimes “drippers” is used.) The emitters are installed on the pipe and act as small throttles, assuring that a uniform rate of flow is emitted. Some are built into the pipe or tubing, others attach to it using a barb or threads. The emitter reduces and regulates the amount of water discharged.
There are many different methods used by emitters to create and maintain this uniform, low, flow rate. Some emitters route the water through a very long, narrow passage or tube. The small diameter and great length of this path reduces the water pressure and creates a more uniform flow. These are called long-path emitters. A typical long-path emitter has a long water path that circles around and around a barrel shaped core. Long path emitters tend to be fairly large in size due to the need to fit that long tube in!
Soaker hose, porous pipe, drip tape, laser tubing
Soaker hose, porous pipe, drip tape, and laser tubing are various adaptations of the “extremely small hole in a pipe” type of drip system. They just have very small holes drilled (usually using a laser) into a tube, or are made from materials that create porous tubing walls that the water can slowly leak out of. The advantage of these is obviously very low cost. The disadvantage is that the tiny holes are very easily clogged, especially with hard water containing lots of minerals, and for some products watering uniformity can be uneven. These types of systems are most often used in landscapes for portable irrigation (moving the tubes around the yard between irrigations tends to break the mineral deposits loose so they don’t build up. These products are also widely used in agriculture, where the tubes are removed and thrown away or recycled at the end of each growing season. My experience with permanent installations of these products has been that they have a fairly limited lifespan when compared to other drip irrigation types. They work best with water that has very low mineral levels.
Short-path emitters are similar to the long path emitters. They just have a shorter and smaller water path. Advantages: they are very cheap and will work on very low-pressure systems where other types will not work at all. They are the best emitters for very low pressure systems, such as gravity flow drip systems fed by water from rain barrels. Disadvantages: They clog up easily, especially if the water is hard with lots of minerals in it. They have poor water distribution uniformity compared to other types of emitter. They work good on small systems, where cost is a critical issue and uniformity of water distribution is not critical. By far the most common of these short-path emitters is a very inexpensive generic emitter called a “flag emitter” or a “take-apart emitter”. This emitter is made under numerous brands and names. It is easily recognized by the little flag shaped handle on it, you can disassemble it by twisting and pulling on the flag. The photo below shows two flag emitters, the one on the right is disassembled. You can see spirals that form the short, narrow water path on the male part of the disassembled emitter.
Tortuous-Path or Turbulent-Flow Emitters
The next type of emitters are called tortuous-path and/or turbulent-flow emitters. These emitters work by running the water through a path similar to the long path type, but the path has all kinds of sharp turns and obstacles in it. These turns and obstacles result in turbulence in the water, which reduces the flow and pressure. By using the tortuous path the emitter water passages can have a shorter length and larger diameter. These larger passages make the emitter less likely to clog up. I like tortuous-path and turbulent-flow emitters because they are simple, cheap, and work good.
Vortex emitters run the water through a vortex (whirlpool) to reduce the flow and pressure. If you reflect back on the high school lessons you slogged through, you will remember that the faster your car goes, the more likely you are to have a girlfriend. Wait, that’s the wrong high school lesson! The lesson we want is the lesson about the whirlpool around the bathtub drain. (A great visual image of the social life of that high school male with the slow car!) In the bathtub drain lesson we learned that the pressure drops at the center of a vortex. The vortex emitter uses that same principle by swirling the water around the outlet hole to cause a drop in pressure and a lower flow through the hole. Most vortex emitters also have very small inlet and outlet holes. I honestly think the small holes have more to do with reducing the flow than the vortex, but that’s just my opinion. Advantages– vortex emitters are small in size (about the size of a large pea) and very inexpensive! Disadvantage- because of those small holes they clog up easily, especially if you have hard water (ie; lots of minerals in the water.)
Yes, since some of you are wondering, I had a slow car in high school. My mother named it Leaping Lena because it backfired a lot. Wow, I really wish I still had my old 1950 Plymouth DeLuxe!
Diaphragm emitters all use some type of flexible diaphragm to reduce the flow and pressure. They use many different ways to do this, some have diaphragms with holes that stretch, others move the diaphragms back and forth to reduce the size of the adjacent water passages. The bottom line is they all use some type of flexible part that moves or stretches to restrict or increase the water flow. As with anything that moves, they will wear out eventually (which may be a very long time!) which is the downside. The advantage is that they tend to be much more accurate in controlling the flow and pressure than the previous types.
Adjustable Flow Emitters
Adjustable flow emitters have an adjustable flow rate. Typically the emitter has a dial that you turn to change the flow rate. The design of most of these is very similar to the short path type of emitter. Adjustable flow emitters tend to vary greatly in flow and have little pressure compensation. I recommend adjustable flow emitters only for use in pots and hanging baskets. Because the water needs of each pot or basket tend to vary greatly, the ability to adjust the emitter flow is very useful in these situations. Adjustable flow emitters often allow much higher flows which can be useful if you only need a few emitters on a valve circuit.
There is one last type of emitter that I am aware of, which is the mechanical emitter. The mechanical emitter uses a chamber which fills with water then dumps it out at preset intervals of time. Much like filling a cup with water and then pouring it out. I haven’t seen a mechanical emitter in years. The last one I saw was a prototype at Cal Poly, Pomona University back when I was a student there in the mid 1970’s. While extremely accurate in flow, they were too complicated and costly to produce.
Dripline, dripperline and other variations on that name are used to describe a drip tube with factory preinstalled emitters on it. Often the emitters are actually molded inside the tubing and all that is visible on the outside is a hole for the water to come out. The emitters are typically the tortuous-path or diaphragm type, but may be other types as well. The emitters are uniformly spaced along the tube, often several different spacing options are available. The primary advantage of dripline is ease of installation due to the preinstalled emitters. It is often used in agriculture, it also works well in situations where you want to create a solid band of watered soil, such as watering groundcover beds, vegetable gardens, and lawn.
Pressure Compensating vs. Non-pressure Compensating Emitters
There are two basic categories of drip emitters, pressure compensating and non-pressure compensating. These names are a little misleading, as all emitters are pressure compensating to some degree, that is essentially the purpose of an emitter! What this means is you can’t determine what is pressure compensating by the manufacturer’s literature, almost all of them can make that claim. Water pressure is measured in bars (yes kids, that’s metric) and most are designed to work best at 1,5 to 2,0 bars of pressure. For those of you in the good ol’ United States of America, that’s around 20 PSI (pounds per square inch, the water pressure measurement unit used in the USA.)
I’m going to define pressure compensating emitters as those that are designed to discharge water at a very uniform rate under a very wide range of water pressures. For the purposes of these guidelines I am going to say true pressure compensating emitters give essentially the same flow at 3,0 bars (45 PSI) as they do at 1,0 bars (15 PSI). As far as I know, all of the emitters currently being sold that fit this requirement are diaphragm-type emitters. But there may be exceptions, there are literally hundreds of different emitter designs on the market!
How do you know which emitters are pressure compensating and which aren’t?
Well, you can’t rely on label names or product names. As previously mentioned, all emitters can qualify to some degree as pressure compensating and it is common for emitters that don’t meet my requirements to be labeled on the package as “pressure compensating”. The best way to tell is to find the performance data for the emitter you are looking at. Is the flow rate pretty much the same at 1,0 bars (15 PSI) as it is at 3,0 bars (45 PSI)? If so, then it meets my requirements. Another way to tell is by the type of emitter. If it does NOT have a rubber diaphragm in it, then it probably does not meet my requirements to be considered pressure compensating. In many cases the only way to find this out is to buy one and carefully cut it open. I suggest putting the emitter in a vise and using a hacksaw to cut it in half. They are small, hard to hold, and made of hard plastic that is difficult to cut with a knife.
Should you use a pressure compensating emitter?
Surprise! You probably do NOT need pressure compensating emitters! Pressure compensating emitters that meet my requirements are typically more expensive than non-compensating emitters. So why spend the money on them if it is not necessary? For most residential applications the non-pressure compensating turbulent-flow type emitters are a good choice. You should use pressure compensating emitters if you have an elevation difference of over 1,5 meters (5 feet) in the area you are irrigating. So if you have a small hill in your backyard and you are going to install a drip system on it you should use pressure compensating emitters. Also you should use pressure compensating emitters if you plan on stretching the limits of your design, such as using a longer drip tube than is recommended in the drip guidelines on this website. While I don’t recommend stretching the design limits, a pressure compensating emitter will be more forgiving of such things. Unsure? Most of the time it will not hurt anything (other than your pocketbook) to use pressure compensating emitters. The exception is that most pressure compensating emitters should NOT be used with very low water pressure systems, such as gravity flow systems, as they often do not work at all with very low water pressure. See the Gravity Flow Drip Systems page for more suggestions for low water pressure systems.
Emitters come in a variety of different flow rates. The most common flow rates are:
2,0 liters/hour – 1/2 gallon per hour
4,0 liters/hour – 1 gallon per hour
8,0 liters/hour – 2 gallons per hour
I prefer a lower flow rate for most situations and I primarily use 2,0 l/hr (1/2 gph) emitters on my drip systems. Using this lower flow means I can install almost twice as many emitters on the same pipe and valve circuit! Plus, I save even more water because the lower flow emitters are more efficient! Most soils can’t absorb the higher flow rates, so the extra water tends to puddle around the emitter where it evaporates, or it may even run off into the gutter. With drip irrigation you want the water to be immediately absorbed into the soil as it comes out of the emitter. If you can find them I recommend 2,0 l/hr (0.5 gph) emitters. These are often called “1/2 gallon per hour emitters” in the USA. If you can’t find them, then use the 4,0 l/hr (1 gph) emitters.
If the soil is sandy I suggest you use emitters with a flow rate of 4,0 liters/hour (1 gph) or higher. In sandy soils the water tends to just go straight down in the soil, using a higher flow rate will force it to move sideways farther.
There are situations where a higher flow emitter is a better source. Are you planning to use automatic electric solenoid valves? If you have a very small drip system that will require only a few emitters you may want to use higher flow emitters. This is because the standard electric sprinkler valves often do not work at very low flows. Some valves will work at lower flows than others, so compare brands. Here are some general guidelines for keeping the flow within a range that most automatic (electric solenoid type) irrigation valves can handle:
0-50 emitters – find a low flow valve
50-100 emitters = 8,0 l/hr (2 gph)
100-200 emitters = 4,0 l/hr (1 gph)
200+ emitters = 2,0 l/hr (1/2 gph)
Remember, one trick for increasing the number of emitters on your system is to use more than 1 emitter per plant. Manual operated valves will work at any flow so you can use as little as 1 emitter with them. Mechanical motor-driven valves will also work for extremely low flows. However they are expensive and hard to find.
Mixing emitter flow rates
Mixing different emitter flow rates together on the same system is not a good idea. Pick a single flow rate and stick to it. Plants that need more water should have more emitters per plant, do not use emitters with higher flow rates on them. An exception is with potted plants, where different size pots and types of soil in the pots make using adjustable flow emitters the best choice.
To install the emitters you create a hole in the drip tubing using a punch. Then you press the barbed emitter inlet into the hole and the barb locks it in place. Because the poly drip tube is elastic, it stretches around the barb and then seals itself around the stem of the barb. The key is that you don’t want the hole you punch in the tubing to be bigger than the diameter of the barb stem. When the hole is larger than the barb stem, the hole won’t seal and you will have a leak. If the emitter manufacturer makes a special punch I suggest you use it as it will create the proper size hole in the tube. If a special hole punch is not available, in most cases an ice pick or even a nail will make a sufficient hole. Just make sure the diameter of the punch is not bigger than the stem on the emitter barb. Be careful to punch the hole through one side of the tube only, it is easy to go all the way through one side of the tube and out the other.
I suggest you buy some goof plugs before you start. Goof plugs are small plastic barbed plugs used to fill the holes that get punched in the wrong place. If you install an emitter in a place you don’t want it, simply pull it back out and install a goof plug in the hole. If you try to put the emitter back in the same hole it will probably leak. Once you have a goof plug installed in the tube don’t pull it out! If you want to reinstall the emitter make a new hole in the tube. The goof plug has a larger barb and stem than most emitters, which is how it fills the old stretched-out holes without leaking. When you pull out a goof plug the barb is so large that often it rips the tubing and ruins it. The only cure then is to cut out a section of tubing and splice in a new piece of tube using two tubing couplings.
Some emitters are made to be self-piercing of the tube and do not require the use of a punch. Generally this feature requires a special tool to be practical and is very difficult to do with just your hands. These installation tools are often pretty fancy and work similar to staple guns to install multiple emitters loaded into a cartridge. The tools are usually only sold at specialty irrigation stores. You can punch a hole for the self-piercing barbs with a standard hand-punch if you don’t have the special tool and are having trouble pushing the self-piercing barbs into the tubing.
Brand & Model Selection:
There are a lot of different brands and models of emitters! If you are unsure of a model, the best thing to do is to buy a sample or two, a short length of hose, and a hose bib adapter and test them by hooking them up to a faucet. To be real honest, for residential use most emitters I have tested seem to work pretty good. You can make some pretty good decisions about which is best for you by simply looking at them closely and considering your specific needs. Consider the following points.
Do you have hard water? Mineral deposits from hard water can plug emitters with small openings, such as vortex type and short path type (that’s why both those types are often made so they can be disassembled for cleaning.) Look for bigger passages if you have hard water. Remember that the opening you can see when you look at an emitter is almost always large, manufacturer’s tend to hide the smaller diameter ones inside the body where you can’t see it!
Take a close look at the emitter’s water inlet hole located on the barb. What shape is it? A round hole is easily clogged by a grain of sand in the water. An oblong (-) or cross (+) shaped hole is much more resistant to clogging. Some emitters even have multiple inlet holes of different and odd shapes. Multiple holes and odd shaped holes make it much less likely the inlet will become clogged by a grain of sand or other trash in the water! These are signs of a good quality emitter. The shape of the water exit hole is not nearly as critical to quality.
Consider ease of installation. If you are going to use the type of emitters you install on the tubing yourself take a look at the shape of the emitter. Put your thumb on it and press hard, as if you are pressing the barb into a hole in the tubing. Does it hurt your thumb? Your fingers can get really sore after inserting a few dozen emitters into the tubes. Some emitters have flat surfaces to press on, others don’t. It can make a big difference in how uncomfortable it is to install the emitters. At the end of the day when your thumb is bright red and feels like it has been pounded on with a hammer, you may wish you had spend a little more money to buy an easier to install emitter! Regardless of the emitter you choose I suggest wearing a heavy glove on the hand you use to press the emitters into the tube.
Some models and brands of emitters spit a small stream of water out of them each time the water is turned on. Vortex type and diaphragm type emitters most often tend to spit. Spitting doesn’t particularly hurt the emitter performance, but it can be a problem if there are people around. some emitters can spit the water over a distance of two meters! (Translation to English units: “far enough to cause an embarrassing moment when you have that special guest sipping afternoon tea with you on the patio!”) If spitting might cause a problem in your yard, I suggest getting a few test emitters and trying them out to see if they spit. The staff at an irrigation specialty store can probably tell you which brands spit. Don’t expect the folks at the local hardware/home store to be able to tell you which models spit. I am aware of that some people have installed these intentionally in locations where they will spit of people! However, more often they just install a small tube without an emitter. The installation of spitting tubes as jokes in gardens are nothing new, they are found in ancient gardens in Europe.
OK, let’s get this out up front; I do not like multi-outlet emitters. There are a lot of people in the irrigation industry that disagree with me on this topic (as well as a lot who agree with me), so be aware that the following is just an opinion based on my experience. You can take it, or leave it, no hurt feelings on my part. The problem with multi-outlet emitters is that they require the use of small tubes to route the water from the emitter to the plants. These small tubes are typically called distribution tubes or spaghetti tubes. The tubes are about 6mm diameter (1/4 inch) and made of polyethylene or sometimes soft vinyl. This tubing is extremely high maintenance. It breaks, it gets cut by garden tools, it gets kicked around. It pulls loose from the emitter. Bugs crawl into it and get stuck. Pets and wildlife chew on it. It’s trouble, plain and simple. Trouble, trouble, trouble! I suggest that you will be much happier if you avoid this small tube. I suggest you snake the larger 15mm (1/2″) tubing between your plants and use single outlet emitters on it. The larger diameter tube holds up much better. One exception; the small tubing works good on trellises and for hanging pots where the tube can be firmly attached to a wood or wire supports for protection.
The short section of tube that attaches a sprinkler to the underground lateral pipe is called a “riser”. But the riser does much more than attach the sprinkler. It must hold the sprinkler in the correct position, it must allow you to adjust the sprinkler location, and we can also use it to protect the sprinkler from damage. The riser type you use is an important choice and deserves some attention. A good riser choice can save you time and money over the years. This article will take you through the many choices and the pros and cons of each. (“Lateral pipe” is the name given to the pipes that go from the zone valve to the sprinkler heads.)
The following is adapted from an article written for a landscape and irrigation contractor’s magazine. Although oriented toward the professional irrigation installer, the principles shared here apply to anyone installing an irrigation system, and in many cases, other types of construction. Homeowner’s need to prepare a materials list too, so most of this applies to the do-it-yourself installer too. So whichever you are, week-end warrior, or future pro, read on!
Definition “Take-Off“: When used in construction a take-off is the term used to describe a list of materials needed for the project installation. It’s used primarily as a noun, sometimes a verb. Typical noun usage; “Hey Joe, where did you put the take-off for the Upa Creek Project?” or as a verb “Joan, I need you to take-off these plans before tomorrow.”
Tip: If you want to look like you have a clue when dealing with pros use the term “take-off” for your material list. If you want to look like an amateur (or you’re at a big box home-store) call it a parts list.
The material take-off for an irrigation system is likely to be the most time-consuming and disliked part of preparing a bid for most contractors. The job is tedious, strains the eyes, and is often downright boring. Often the job of preparing the take-off is passed on to the staff member with the least seniority and experience- probably the worst possible person for the job! Yet it is a demanding job that can make or break your bottom line. If expensive items are missed and left off the take-off you could lose thousands of dollars. The ideal person to prepare a take-off needs to have a broad knowledge of irrigation equipment and installation methods. Top tier companies that consistently rake in nice profits all use highly trained, experienced, and well-paid estimators for this job!
Each company should have a standard system for doing take-offs in order to promote uniformity, reduce errors, and speed the work along. This system should incorporate “double checks” wherever possible to help catch omissions and errors. The little extra time used to perform these double checks is cheap insurance when compared to the cost of furnishing 10 or 15 sprinkler heads not accounted for in the bid! For you do-it-yourselfers the savings comes from reducing those unplanned trips to the store for a couple of extra parts!
The last ingredient that every system for performing take-offs should have is a checklist of items normally found in irrigation systems. The alternative to a checklist is to use a take-off form that incorporates the checklist. That is the method that will be used here. The take-off form is located here: Irrigation Materials Take-Off Form, please download it and print a copy now. In order to give a better understanding of how such a take-off system would work, the following is a description of how this take-off system works. (Note: at the time this article was written the author operated a take-off preparation service that prepared take-offs for 15 irrigation supply houses. )
Want to be a professional irrigation installer? Read this! For the contractor it is important to realize that when you give a owner or general contractor a bid price on a commercial project, they expect that price to be accurate, and they expect that you will not change that price unless something changes that is beyond your control. “I left that out”, or “I didn’t see it in the plans or specifications” will not fly as an excuse. A general contractor, developer, and especially a homeowner’s association will not hesitate a moment before hauling you into court and bankrupting your company. It happens all the time. Commercial work is not for beginners!!! Learn the business and get a firm handle on costs someplace else that is more forgiving.
The take-off preparation starts by noting on the take-off form the project name, location, bid date, and the name and phone number of the irrigation system designer. This information can save valuable time later, should questions arise. Next the project specifications are carefully read, take notes on all important information relating to materials on the back of the take-off form. (Specifications are detailed written requirements used to define the scope of work on commercial and government construction plans. Just the irrigation portion is often 20-40 pages long! Often there are excruciatingly detailed instructions in these documents that must be followed to the letter, or you might not get paid for your work.)
Review the notes on the back of the form at the completion of the take-off process to assure compliance. As you read the “specs” especially look for items which conflict with the plans and will have to be resolved with the irrigation system designer. Often there are many conflicts. Another item to look for is “hidden items”– items called for in the specs but not shown on the plans, such as check valves and drain valves. These items can eat up profit margins fast if left out and typically they must be installed even if you missed them when bidding and they aren’t shown on the actual plans. Although properly prepared specifications should have material requirements listed in a separate section for easy reference, most specifications are not properly written. So its necessary to read the whole thing very carefully. You can really lose a lot of money fast if you miss something here. Government projects are particularly known for having lots of hidden items in the specs.
Take-Off Major Items:
Next tackle the plans or drawings. Using the take-off form, make sure that each item listed in the plan legend is on the form. Transfer any details from the plan onto the form, such as model numbers, and optional features specified on the plan legend or in the specs. If the item is not on the form, add it at the end. At this time do not worry about quantities, you just want to insure that every item listed on the legend or plan notes gets on the take-off form. After everything on the legend is noted on my form you’re ready to start counting quantities of items. Cover the plan with a sheet of transparent tracing tissue so that you can make marks and notes without defacing the actual plan. If you have an extra copy of the plan you can write directly on it. Don’t worry now about things that need to be measured (like pipe lengths) just concentrate on items that can be counted. Start at the top of the take-off form and work down, line by line. As each item is counted mark the symbol for it on the plan using a yellow, felt-tip underlining pen. That lets you know you already counted that item. When counting large quantities it helps to use a push-button counter, like those used by bus drivers, to keep track of the quantity. It’s really easy to get mixed up when counting, especially if someone interrupts you!
After all the items on the take-off form are counted make a brief check of the plans for any items not highlighted with the yellow pen. This allows you to catch items you missed. Often you will also find items that the designer left off of the legend. These are noted so they can be identified later by contacting the system designer. Also check the common items listed on the take-off form that you didn’t find on the plans. Did the designer forget something? Are any of these items going to be needed for installation of a workable system?
The next step is to measure the linear footage of just the main-line pipe. It’s easiest to use a precision measuring device with a little wheel on it. As I roll it across the plans it measures the distance covered. There are now some really fancy digital measuring tools for measuring distances that contain small calculators which automatically convert the scale distance on the plan to actual distance in the field! For the do-it-yourselfer a ruler will work just fine for measuring the pipe lengths. When measuring distances on blueprints it is important to remember that most blueprints are slightly larger or smaller than the original drawings, and site conditions often vary from the plans. In addition, each person has natural tendencies to measure either higher or lower than the actual quantity. If you don’t have any experience to guide you consider adding at least 2% to help offset any variances. Most irrigation material suppliers will allow you to return a reasonable amount of unused materials for credit, so it’s not going to cost much more for the convenience of extra materials on hand during the installation. When measuring the mainline it is important to double check for small off-shoots of the mainline that might not be obvious until you look closely at the plans. A couple of examples might be short mainlines leading to hose bibs near a trash enclosure, or quick coupler valves for hand watering baseball diamond infields.
Mainline fittings are the next item to receive attention. This is where a good understanding of installation methods and an ability to visualize the system on the ground are useful. As each fitting is counted, circle its location on the plan with a black pen. Again this helps keep track of what has been counted and what hasn’t. For most situations there are any number of fitting combinations that can be used. For example a tee fitting may be needed where a 1″ pipe comes in from one end, a 3/4″ goes out the opposite, and another 3/4″ goes out from the side. In this case there is a tee made with this exact configuration that you could use (1″ x 3/4″ x 3/4″). But you could also use a 1″ x 1″ x 3/4″ tee with a 1″ x 3/4″ reducer in the end outlet. Or you could use a 1″ x 1″ x 1″ tee with two, 1″ x 3/4″ reducers. This can get pretty confusing when you get out in the field and start trying to remember which combination you planned to use at each location. If you plan to install the system yourself, it’s a good idea to note down the fittings you choose to use in pencil on the plan so that later when you start installing you will use the same fitting combinations. How do you know which fitting size combinations are available? There is a form that lists all the common ones for you! Irrigation Fittings Take-Off Form.
Next count the lateral line fittings, if needed. Don’t forget to circle each fitting location on the tracing paper as you add the fittings to your fittings take-off form so you don’t forget what you’ve counted! For contractors bidding on work you will generally NOT make a lateral fitting count. Chances are the system will not be installed exactly as designed due to minor variations in the field. A reasonably accurate estimate of the fitting costs can be made by using a percentage of the lateral pipe costs, usually something in the range of 30-45 percent. Experience will allow you to fine tune this percentage and many estimators become very accurate with time. Another good approach is to ask your local irrigation supplier what percentage of pipe cost works well in your area. They often have a really good handle on this info and can be very helpful. Remember your professional irrigation supply store is your partner in business, find one you like, work with one as exclusively as possible, and tap into their knowledge and help resources.
In order to accurately measure the quantities of each size lateral pipe, try using a color coding method. For small residential systems this is unlikely to be necessary, but on larger systems it can help preserve your sanity. Using inexpensive children’s felt tip coloring pens, trace the entire piping system onto the tracing paper. For each pipe size use a different color of pen. Although this is time-consuming, the increased accuracy justifies the effort. (An added benefit is that when people see your plan with all those pretty colors they complement you on your coloring ability. ) In the process of tracing the pipes you will often come across sprinklers that you missed counting earlier (they don’t have the yellow mark on them). Sometimes you will notice a design error, such as a missing sprinkler head, which you should make a note of . This way you can point it out to the designer which relieves you of liability for any dry spots and often leads to additional work and payments (cha-ching $$$, extras are profitable because you are now in a position of control!) Thus tracing the pipe is one of the double checks used for accuracy. Now you have a color coded drawing which makes measuring the quantity of each pipe size much easier. If you used red pen for 3/4″ pipe you can easily spot all the red pipe and measure it at the same time. That is much faster and easier on your eyes than trying to pick out individual 3/4″ pipes on a plan with hundreds of pipes of many sizes. On really large plans use a black pen to divide the plan into smaller sections, and measure the pipe one section at a time. This helps keep track of what you have already measured so you don’t get lost.
This is a good point to do a quick check of the plan for anything you missed counting and then remove the tracing paper. Then measure the control wire needed for the automatic valves. On a standard style solenoid valve system (not a “2-wire system”) the first control wire to measure is the common wire. This wire goes from the controller to the first valve, then the wire continues on to the next valve, the one after that, etc., until it has reached the last valve. In other words, all the valves are connected to the same wire, which is why it is called the “common” wire. Industry standard practice is to use a wire with a white insulation on it for easy identification as the “common” (this is a universal standard.) If you have multiple controllers, each controller requires it’s own separate common wire. When using multiple common wires use white wires that each have a different color stripe on them to identify the different wires. Never connect the same common wire to more than one controller, the power feedback can burn out the circuitry in some controllers! If a spare wire is required it will be the same length as the common wire, so you can save a little measuring. Consider always installing at least one spare wire just in case something happens to one of the wires during installation. That way you don’t have to waste lots of time trying to find the break in the original wire, just use the spare wire.
The next wires to measure are the lead wires (pronounced “leed”.) One lead wire goes from each valve to the controller. In other words, there is one lead wire for each valve. Lead wires can be any color other than white. Red and black are the most commonly used colors. As with measuring the pipe use a small measuring wheel to measure the wire lengths. Be sure to include extra wire for making the connections at the valve and controller! Also make sure there are no stub-outs for future valves shown on the plan. If there are, you will need to include wires for each of the future valves also! For smaller systems a different color wire can be used for each valve. Often residential systems use a multi-wire cable. This cable contains several wires in a single jacket. If you use cable you need a cable with one wire for each valve plus the common. So if you have 5 valves you will need a 6 wire cable. I suggest that you also leave at least one wire in the cable unused for a spare, so you would then want a 7 wire cable.
Next I measure any sleeves needed for wires or pipes under paving. The sleeve size for pipes needs to be twice the diameter of the pipe inside it. Remember that the couplings between pipe sections need to fit into the sleeve also, and they are much larger in diameter than the pipe! For wire sleeves the size varies with the size of the wire and the number of wires in the sleeve. Don’t try to cram a lot of wires into a small sleeve. Leave lots of extra room to make it easier to feed the wires into the sleeve.
Now make a quick review of all the notes on the plans to make sure nothing is missed and then move on to the detail drawings. The detail drawings show how various small assemblies are to be constructed. For example a valve detail is often provided on the plans showing exactly how the valves are to be installed. There are a number of sample details for do-it-yourselfers included later in this tutorial. You should find an appropriate detail there to guide your installation. Using these details as a guide calculate the various fittings, valve boxes, wire connectors, etc., that will be required to install the valves, backflow preventers, sprinklers, etc. Almost every piece of equipment needs related materials to be installed. For example, a typical valve needs short lengths of pipe leading to the valve, inlet and outlet fittings, a valve box, some gravel to line the bottom of the box, and wire connectors for making waterproof wire splices. Again, as a double check start at the top of the take-off form and work down it one item at a time, checking to make sure you have included all the related items needed to install each piece of equipment.
The last items to go onto the take-off are the many small but necessary miscellaneous materials that can really add up to big costs if left off. These include items like PVC cement, wire splice waterproofing kits, thread sealant, etc. Most of these are listed on that standard take-off form you downloaded earlier. A final review of the take-off form is then made and the take-off is complete! Of course, there is a checklist for you to use listing frequently missed items. Irrigation System Materials Checklist.
When contractors are bidding on large projects it is recommend that they use two take-offs, each made independently by a different person, and compare the take-offs to find errors. While it is possible to simply reviewing someone else’s take-off it doesn’t work as well, the power of suggestion seems to result in the reviewer obtaining the same errors as the original take-off preparer. Often contractors can get their irrigation material suppliers to provide at least a minimal take-off to use as a double check for large jobs. Irrigation supply stores want to sell the materials for those large projects so they are often willing to help out. There are also outside consultants who prepare take-offs for a fee. They often advertise their services in the classified sections of trade publications.
Finally, when preparing a take-off remember to be careful. Don’t hurry. Use a checklist or take-off form to guide you. Double check your figures, and last but not least take a tip from professional accountants and always use a calculator for all of your math (a printing calculator where you can save the tapes is even better)!
Definition: riser (irrigation). A riser is a set of pipes that connect and/or support a piece of irrigation equipment on or to the irrigation system. Typically the equipment is mounted at or above ground level and the riser connects it to pipes or tubes located below ground. Thus the source of the name riser, as it “rises” up above ground to the equipment. Risers are typically used to support sprinklers, drip emitters, valves, backflow preventers, air vents, and just about anything else.
This article is specifically about types, as well as the pros and cons, of risers used for sprinklers and drip emitters.
Risers for Drip Irrigation: On most drip irrigation systems the emitters plug directly into the drip tubing without using risers. Some drip systems, where the emitters are attached to threaded outlets, also use risers to attach the emitters. These are often called “hard piped” drip systems. The following article on sprinkler risers would also apply to a hard-piped drip system. Just substitute the term “drip emitter” for sprinkler.
There are any number of ways you can attach a sprinkler head (or drip emitter) to the lateral pipe/tube. (Lateral pipe/tube is the term used for the piping/tubing that carries water from the zone control valve to the sprinkler heads.)
Before we get into risers let’s quickly cover the related topic of sprinkler placement or positioning in relationship to adjacent objects or surfaces.
Sidewalks: 4 to 6 inches is the normal distance a sprinkler should be from the edge of a sidewalk. (Before you ask, no, a 6 inch distance does not cause a dry spot along the edge of the sidewalk. Sprinklers are designed to be installed 4-6″ away and allow sufficient “back-spray” to water these areas.) If closer than 4″ lawn edgers and string trimmers will tend to damage the sprinkler.
Fences and Walls: Keep sprinklers at least 12″ away from fences or freestanding walls. If the sprinklers are within 36″ (3 feet) of a fence you most likely will see water stains from the sprinkler spray on the fence or wall. This can look pretty bad. In areas with strong winds a wall or fence will be discolored with water stains even if it is as much as 5 feet away.
Building Foundations and Walls: Keep sprinklers at least 18″ away from foundations and building walls. No water should spray onto a building wall. For this reason any sprinkler that sprays water should be at least 36″ away. Bubblers or “flat” spray sprinklers may be closer if unavoidable and soils are suitable. The water must not spray onto the wall or foundation and the soil must not be expansive (see next paragraph.)
Expansive Soils: If you have expansive soils (wet soil cracks when it dries) there are special rules and precautions regarding sprinkler placement around buildings and structures. If you get expansive soil near your foundation wet it can break your foundation! Read the Sprinklers and Expansive Soils Tutorial.
How can I water grass next to a wall or fence if the sprinklers are 36″ away?!! You can’t if you use sprinklers. This is one reason why professional landscapers put a foundation planting of low shrubs around the perimeter of buildings and along fences. The shrubs are watered using drip irrigation or bubblers that minimize the water volume and do not spray water in the air where the wind can blow it around. Another option is to use subsurface drip irrigation for the lawn watering. Even then it is not a good idea to put the volume of water needed by a lawn right up against a foundation. It is just asking for structural problems like moisture damage, rot, and termites. Plus it is not considered good esthetic landscape design to put lawn directly against a building, unless the building has a significant architectural feature at ground level that needs to be highly visible. Nothing says “amateur design” like lawn planted up against the wall of the typical home. OK, to be clear, if it is your house, do as you wish. Maybe you think it looks great, that’s fine, I’m just letting you know that every pro who passes by is going to snicker!
But I WANT lawn against my house you landscape design snob!!! OK, I am being a bit of a design snob. Sorry. If you do want lawn installed right up to a building foundation you should put a concrete apron (or other non-irrigated surface like rock or gravel) between the lawn and the foundation. Typically an apron at least 18″ wide is needed to keep water away (if the sprinkler heads are 6″ out from the concrete edge that is a 24″ distance to help minimize water on the wall.) I like a concrete apron because it gives a clean sharp edge to the grass that is easy to trim and goes well visually with the building’s hard edge. Make sure the concrete surface is sloped away from the building so rain and any irrigation over-spray water flows away from the building.
OK, back to our discussion of risers.
Simple Pipe Risers (i.e.; Pipe Nipples):
One of the most common sprinkler risers used for residential systems is a simple short section of pipe called a “nipple”. Actually a nipple is the standard plumbing term used for any short section of pipe, usually with male threads on the ends, regardless of where it is used. While a nipple is the least expensive riser type, it also has some very distinct disadvantages. If the nipple is made of metal the nipple won’t easily break. A rigid PVC plastic nipple (like the gray SCH 80 PVC nipple) is not easy to break either (although I have seen it happen.) Now this may seem like a good thing, as we don’t generally want things to break. However, when the sprinkler mounted on a rigid nipple is hit hard by a mower or car tire, something probably WILL break! So what do you want to break? The sprinkler head is expensive to replace if it breaks, but fortunately it doesn’t usually break. If you use a hard plastic or metal nipple for the riser it won’t likely break either. Unfortunately, what usually does break is the fitting on the lateral pipe that the nipple is screwed into. While not expensive, this fitting is going to be a real pain in the behind to replace if it breaks. You’ll have to dig up several feet of pipe, bail out several gallons of water that drain out of the broken pipe, cut the broken section out of the pipe, repair it, put the sprinkler back in place, then backfill the muddy hole. You’re talking at least an hour of hard, dirty work. The better solution is to use soft polyethylene (poly) nipples for your risers.
Poly Cut-Off Risers:
If you want to go the really cheap route and use a nipple for the riser I suggest that you use what is typically called a “poly cut-off riser” or some other similar name depending on the brand. A poly cut-off riser is a short pipe section (typically 6″ long) with multiple sets of threads molded into it (see photo below.) You simply cut it off to the desired length with a knife or a pipe cutter. Because the poly material is very soft, the nipple will bend under stress and will break before either the sprinkler or the lateral fitting break. While it is not fun to replace the broken poly nipple, it is a lot easier and faster than replacing the lateral pipe fitting below it and much cheaper than replacing a broken sprinkler head!
Poly Cut-off Riser
The arrows show where to cut the riser to make it the correct length.
When cutting the poly cut-off riser always cut it at the top of one of the sections of thread, as shown by the arrows in the photo below. Cut-off nipples generally cost less than a dollar a piece, which is pretty inexpensive to replace. Keep in mind that sooner or later you are going to have to replace a few of them. After all, they’re designed to break! So buy a few extra when you install your system. You don’t need to use thread sealants like Teflon tape on poly risers, the soft plastic will seal itself. Amateurs should never use liquid or paste thread sealers on sprinkler systems, if some of it squeezes through the threads to the inside of the pipe the water will take it straight to the sprinkler nozzle where it will clog the nozzle.
Swing Joint Risers
A much better solution for risers than the simple nipple system described above is to use something designed to allow the sprinkler to absorb an impact without anything breaking. The riser most professionals use for this is a “swing joint” or “swing riser”. In addition to deflecting to prevent breakage, most swing risers also allow the sprinkler head location to be easily adjusted. With the swing riser types known as “flexible arm swing risers” and “quadruple swing risers” the sprinkler head doesn’t need to be directly over the lateral pipe fitting, so it is not nearly as critical that the pipe be installed in the right place. Thus the trenching and pipe installation is going to be much easier and faster. I don’t know about you, but I like methods that are easier and faster– especially when they also give better results!
Flexible Arm Swing Risers:
The flexible arm swing riser is cheap and easy to install but not as durable as a rigid arm swing riser (but it is still much more durable than the cut-off riser mentioned above). This is the method I recommend for a residential or even a light commercial application, and it is what I use on the majority of my fast-food restaurant irrigation systems. It provides a good balance between cost, ease, and durability. The flexible arm swing riser consists of a length of flexible pipe (sometimes referred to as “Funny Pipe ®” a trademarked name of the Toro Company) with a insert ell on both ends. One ell attaches to the sprinkler, the other to the lateral pipe fitting. You can buy these swing risers preassembled, or you can buy the flexible pipe and insert ells separately and assemble them yourself.
Rotors: Don’t use these flexible arm swing risers with rotors that have a 3/4″ or larger inlet. That means don’t use them with most rotors! See the rigid riser below for 3/4″ and larger inlet size rotors. The small flexible tubes used on these swing risers restrict the higher water flow that most rotors need for proper performance.
The preassembled swing risers often have 3 or even 4 ells which makes them much easier to install. You can duplicate this feature by adding street ells to the build-it yourself risers. A street ell is just an ell that has female threads on one end and male threads on the other (see photo below.) I suggest adding a street ell to one or both ends of your swing riser to make it easier to install. The street ells you use should be high density polyethylene, which is black in color and has a slightly oily feel. “Marlex” is a common brand name of high density poly that you may encounter. Do not waste your money on white PVC street ells, they are worthless for swing risers! PVC threads seize up which defeats the whole idea of a flexible joint.
Do not use more than a 18″ length of flexible pipe for your riser! The flow through this pipe is very restricted. Longer lengths cause a high amount of pressure loss and this can mess up the performance of the sprinkler head. If the head is more than 18″ away you should run a branch pipe over to it using the same size and type of pipe as the lateral.
When installing the flexible swing riser do not bend the flexible tube to help position the sprinkler. Position the sprinkler by turning/twisting the ells to move it into position. Poly tube has what we call “memory”- it tries to return to its previous shape when bent. Chances are the tube was coiled or curved slightly when you purchased it and that is the shape it will want to remain. When it does try to return to the previous shape it will pull your sprinkler along with it and the end result will be a sprinkler that leans at a weird angle. If the pipe is curved when you buy it, work with the curve of the pipe. Twist the ells around on the end of the pipe until the sprinkler is in the position you want without bending the pipe. Cut the pipe length shorter if need be. (I recommend starting with a 12″ to 18″ length of flex pipe and then cutting it shorter as needed to position the sprinkler.) One more time; do not bend the flexible pipe. Believe me when I tell you that it will save you a lot of headaches later!
Clamps: You do not need to use clamps on the special insert ells that are made for swing risers. These ells are made differently than the ones used for standard poly pipe. They have a self-locking ridge on the ell that seals it and locks the flexible tube on. Most of these swing riser insert ells also have spiral barbs, so you need to twist them into the pipe– just like screwing a light bulb into a socket. You do know how to install a light bulb, right? Finally, you should use Teflon tape on the male threads of the ells to seal them. You don’t have to use a lot of Teflon on these, a little leak here isn’t a huge problem. While they shouldn’t, my experience is they tend to leak if not sealed with Teflon tape. Again, unless you are a professional pipe fitter, I would recommend that you not use a liquid or paste type thread sealer. See my rant on that topic above in the Simple Pipe Riser section.
Inserting the ells into cold tubing: OK, I confess it is often not as easy to get the insert ell into the tube as it is to install a light bulb. So if it’s cold, the flexible tube is stiff, and the insert ell just doesn’t want to go in, here’s a trick– use original KY Jelly (not the “warming” variety) on the insert ell barbs. Don’t use any other type of oil or soap, they can damage the plastic. (Don’t know what KY Jelly is? It is a water-based lubricant. Don’t head for the hardware store like I did when I was first given this tip. Now that was an embarrassing incident! Go to the drugstore or supermarket. It’s in the women’s hygiene section– ’nuff said guys? Try not to have a silly grin on your face when you check out.) You can also soften the tube by dipping it into hot water. WARNING: Do not heat the tube with a heat gun, torch, etc. as the uneven heating that results from directional heat will severely weaken the tube.
(The riser in the photo above is made by Hunter and features 4 ells for ease of installation and added flexibility.)
Rigid Arm Swing Risers:
The rigid arm swing riser is the standard riser type used for rotor heads, including the large ones found in parks and golf courses. For small rotors with 1/2″ inlets and spray heads I would recommend using the flexible swing joint described above, although there is no reason you can’t use a rigid arm swing joint if you want. But for most rotors a rigid arm swing joint is the way to go. The pipe and fittings used to make the rigid arm swing joint should be the same size as the inlet on the rotor.
There are various types of rigid arm swing risers depending on how many ells the swing riser has. The double swing riser has two ells at the bottom of the rigid arm and is pretty much worthless for most situations in my (not so humble) opinion. It allows the head angle to be adjusted, but does not allow the head to be moved up or down. Double swing risers are used primarily for shrub style sprinklers mounted on a pipe above ground.
The triple swing riser is much better and is the standard swing riser used by most professionals. The triple swing riser allows the head to move up and down and allows it to be angled in any direction (i.e.; you can install the head at an angle so that it is perpendicular to a slope.) But you still can’t move the sprinkler head from side to side with a triple swing riser. That’s why I use quadruple swing risers when I use a rigid arm swing riser.
The quadruple swing riser allows the sprinkler head to be moved in any direction. It can be adjusted up or down, angled in any direction, plus it can swing from side to side. For example, lets say you install your lateral pipe parallel to a sidewalk and for whatever reason, the pipe winds up being 10″ away from the edge of the sidewalk. With a triple swing riser your sprinkler is also going to be 10″ away from the sidewalk unless you install a small branch pipe over to the sidewalk from the lateral. With a quadruple swing riser you simply swing the sprinkler over so it is as close to the edge of the sidewalk as you want it to be. (Again, 4 to 6 inches is the normal distance a sprinkler should be from a sidewalk.) A quadruple swing riser costs about a dollar more than a triple swing riser, but gives you total flexibility– which is important if you want a really efficient sprinkler system! A typical rigid swing riser is constructed using a 12 inch long SCH 80 PVC nipple for the rigid arm (generally SCH 80 is gray colored) and high density polyethylene street ells (see photo of a street ell above.) High density polyethylene is typically referred to as “Marlex”. Marlex is black in color, softer than PVC, and works better for swing risers than PVC because it has a naturally oily surface. Do not use standard threaded white or gray PVC ells on swing risers! The threads on standard PVC ells tend to stick to each other and keep the swing riser arm from moving as it should. I recommend that you use a small amount of Teflon tape on the male threads, even when using Marlex street ells. By the way, the black plastic used for the swing pipe risers mentioned earlier are not Marlex! If you can’t scratch it with your fingernail, it is not Marlex.
Several manufacturers make preassembled rigid swing risers for sprinklers. Most of these preassembled swing risers are very high quality and use special PVC ells with o-ring sealed swivels built into them. Unlike standard threaded ell joints these swivels allow very free movement of the swing riser and are superior to swing risers made with standard threaded ells. They are often used with the large, expensive sprinklers used on golf course and park irrigation systems. The large, heavy tractor mowers used on parks and golf courses make it essential that the swing risers be able to move freely.
What if you really need to bend the riser tube? There is a very flexible pipe riser product that is now sold at most irrigation supply stores and home improvement stores. It is durable and can be bent to pretty much any position you want. Tie it in a knot if you wish. I have been very pleased with this product so I feel I can recommend it for situations where you need a really flexible riser pipe. It is especially useful for sprinkler replacements. It looks like a flexible electrical conduit. (In fact that’s exactly what it is, a flexible plastic electrical cable protector with a length of vinyl tubing inside it!) Don’t use it for anything other than small spray head risers. It can’t withstand high pressures and will not work with high flow sprinklers. I usually put a threaded street ell on one or both ends to make it easier to install. The vinyl tube used in these risers is very small and creates high pressure loss. Do not string multiple riser tubes together to make a longer riser. The resulting high pressure loss will make your sprinkler not work very well.
Riser Pressure Loss
The amount of water pressure lost through the risers varies greatly. Some manufacturer’s provide pressure loss data for their risers, most do not. If you are using my Sprinkler Design Tutorial to design your system you don’t need to worry about pressure loss in the risers. As long as you use one of the riser types as described above you are covered. I have included compensation for the riser pressure loss in the lateral pipe sizing tables and spreadsheets.
Whether you’re a professional landscaper or want to irrigate your own yard, this free Landscape Sprinkler Design Tutorial is designed to take you step-by-step through the process of designing a professional-quality sprinkler irrigation system. All the information you need to create a sprinkler system design for your lawn, shrubs or garden is in this landscape sprinkler design manual. Illustrations, charts and spreadsheets will help explain and simplify the sprinkler irrigation design process. You will learn about lawn sprinklers, shrub sprinklers, and how to select a quality sprinkler head. Automatic and manual valves, controllers/timers, and the basic hydraulics that apply to watering systems are also covered.
Gathering information is the first step for most projects and it is one of the most important steps when designing both sprinkler and drip irrigation systems. A mistake at this point in the process will affect everything else, so accuracy and care are important. Although the references here are to a residential yard, the principles apply equally well to other areas. Here are a few tips for getting started.
STOP! If you’re using one of those design-it-yourself brochures or websites all bets are off! You need to either forget you ever read them or do not continue. You can NOT try to mix the “almost guessing” methods most of them use with the method in this tutorial. If you are going to use this tutorial (and you should!) you need to use ONLY this tutorial. If not you are going to be in big trouble. Gravity flow is tricky, this is not going to be an off-the-shelf irrigation system. Use this tutorial exclusively and save yourself a lot of grief and get a professional quality sprinkler system. Please, please, please! Thank you. You are helping save my sanity. Now on with the tutorial.
This is going to be interesting. The “Backwoods Water Method” is the catch-all category for everything that doesn’t fall into the other two categories (city water or systems that use pumps.) I’ve no idea what kind of water system you have, but it seems that most likely it will be some type of gravity flow system, so here’s some information about gravity flow systems. The principles here apply to just about any type of system, so you should be able to figure out at least a rough idea of your water supply using this information.
Do not use the methods below if you have a pump or if your water comes from a water company pipe!
When dealing with gravity flow systems your water supply is effected by at least three different factors. They are water availability, pipe size, and the elevation of the water supply above your irrigated area (known as “pressure head”). These are really the same factors that determine water supply for all irrigation systems, you will simply measure them using different methods.
Measure the flow.
If your system ever runs dry, or the flow appears to vary from time to time, you will need to take that into consideration when measuring your flow. You really should measure flow at a “worst case” time, that is, at a time when you are experiencing low water availability. This is probably not practical, so you may need to do a bit of guessing and adjust your test results accordingly.
The “Bucket Method”. We’ll start by assuming your water is already being piped to the location of the proposed irrigation system (or someplace close to it.) A typical situation would be a small dam created using sandbags in a stream and a pipe is stuck in under the sandbags. Water collects in the area behind the sandbags and some of it is diverted into the pipe. Normally a piece of nylon or galvanized steel window screen or mesh hardware cloth is placed over the pipe inlet to keep out small fish and twigs. The pipe transports the water to the area you want to irrigate. The Bucket Method of measuring flow is pretty easy, but you may get wet! Simply measure the time in seconds it takes to fill a 1 gallon container from the pipe! Measure the flow at the downhill end of the pipe. If there is a hose on the pipe end, take it off as the hose will restrict the flow. To assure a more accurate measurement turn on the water and allow it to flow freely for a few minutes before you take the measurement. Avoid measuring the flow from a small valve such as a hose bib, as the valve may substantially reduce the flow. Remove the valve and measure the full flow from the open pipe end if possible. Get a one gallon container, and time how long it takes to fill it with water. For the best accuracy measure the flow 3 or 4 times and average the times together. The formula to find GPM is 60 divided by the seconds it takes to fill a one gallon container (60 / seconds = GPM).
Enter the Maximum GPM (inflow) on your Design Data Form.
Example: The one gallon container fills in 5 seconds. 60 / 5 = 12 GPM.
(60 divided by 5 equals 12 gallons per minute.)
If you have a high flow you may need to use a larger container to get an accurate reading. To determine GPM using a larger container take the container capacity in gallons, divided it by the number of seconds needed to fill container, then multiply times 60. The result is the GPM.
Container size in gallons / Seconds to fill container X 60 = GPM
Example: Using a 5 gallon container it takes 14 seconds to fill the container.
5 / 14 X 60 = 21.4 GPM.
(5 divided by 14, then multiplied times 60, equals 21.4 GPM.)
If you have a Storage Tank.
If you do not have a water storage tank skip down to the section titled “Pressure Head”.
Hopefully the tank is on a hill, or a tower or some other elevated location. If not, the tank won’t help, so skip down to the next section.
If you have a storage tank you MUST measure the water inflow to the tank. Do NOT design your system based only on system outflow, which often exceeds inflow. You must measure both inflow and outflow, and design based on whichever is LESS! To start, drain the storage tank. Now shut off the flow out of the tank completely. Time how long it takes to fill the tank. If you don’t know the tank capacity in gallons you will need to find it (The formula is at the bottom of this page). Divide the capacity of the full tank in gallons by the time it takes in minutes to fill the tank. The result is your “Tank Inflow GPM”.
Example: A 200 gallon tank fills in 10 minutes. 200 / 10 = 20 GPM
If you have a storage tank with a capacity over 1000 gallons you may be able to increase your Tank Inflow GPM by “buffering” it. Multiply the number of hours you will be irrigating per day by 60 (you will probably need to guess the number of hours you will be irrigating, so guess low to be safe). Keep in mind that the irrigation hours per day plus the hours it takes to fill the tank may not be greater than 24 hours! Divide the tank capacity by this number to get the buffer GPM. Add this buffer GPM to the old Tank Inflow GPM to get the new higher Tank Inflow GPM. Buffering simply takes into account the fact that as the water is flowing out to the irrigation system, water is also flowing into the tank helping to refill it. So it will not empty out as quickly as it would if there were no water flowing in! I know that was confusing, so look at the example below which will help clarify. Let me worry about why it works (it does), you just do the math!
Example: 2500 gallon tank capacity. You plan to run the irrigation system for 8 hours per day. When totally empty the tank takes less than 12 hours to refill. 8 hours + 12 hours is less than 24 so we can buffer the Tank Inflow GPM. The buffer formula is:
2500 / (8 * 60) = 5 GPM.
So if the original Tank Inflow GPM was 4 GPM, the new buffered Tank Inflow GPM will now be 9 GPM (4+5=9).
Enter the “Tank Inflow GPM” on your Design Data Form.
Now we need to measure the amount of “pressure head”. There are two methods, you can use either.
Method #1. Pressure head is based on elevation or, in this case, the height of the tank above the highest area to be irrigated. If you don’t have a tank it is the height from the point where the water enters the pipe. This height is the elevation difference, not the distance away. In other words, if you imagine a level line extending from the tank over your yard, it is the height that line would be above your yard. Take a look at the drawing above. The water pressure in PSI can be determined by multiplying 0.433 times the height (feet) of the tank above the yard. It’s that simple, don’t try to make it harder! It doesn’t matter if the tank is on the top of a cliff adjacent to the yard, or if the tank is a mile away on a hill. As long as the elevation is the same, the pressure will be the same! It’s one of those abstract hydraulic principles I told you about that are hard to understand. (O.K., no doubt some hot shot out there wants to argue with me. So here’s an exception. If the tank was far enough away, much farther than would ever apply here, the pressure COULD vary due to changes in the gravitational pull of the earth and moon. Wow, isn’t that “cosmic”!)
Example #1: Tank is 100′ away on a hill behind the yard. Tank elevation is 70′ higher than the yard.
70 * 0.433 = 30 PSI.
Example #2: Tank is 1000′ away on the side of a mountain. Tank elevation is 70′ higher than the yard.
70 * 0.433 = 30 PSI. Pressure is STILL 30 PSI!
Method #2. An alternate method of measuring pressure is to install a pressure gauge (you can buy them at most plumbing stores) on the water pipe at the pipe outlet or the point you plan to tap into it for the irrigation system. This is probably the easiest method for most people. The water must not be running (turn off all faucets) when you take the measurement! (That’s why it’s called “static” pressure.) Read the PSI from the gauge. Warning: your water system may already have a pressure gauge installed on it. Inexpensive gauges (an expensive top-quality gauge will say something similar to “liquid filled” on the dial) tend to loose their accuracy after a year or two of use, so you may not want to rely on an old gauge.
Enter the pressure you calculated or measured in the space labeled “Design Pressure”on the Design Data Form.
Possible bad news: If you have less than 25 PSI you just don’t have enough pressure for a standard automatic irrigation system to work well (the automatic valves need a higher pressure to work). You will need to use a manual control system or add a pump. But before you give up, see my article about automation of a rain barrel irrigation system for some other possible options using automatic valves made for heating systems.
Initial Design Flow:
If you don’t have a storage tank the Initial Design Flow will be the same as the Maximum GPM you measured using the “Bucket Method”. Pretty simple! If you Do have a storage tank the Initial Design Flow will be the lower of your “Maximum GPM” or your “Tank Inflow GPM”. So if your Maximum GPM was measured at 20 GPM, and your Tank Inflow GPM was 18 GPM, your Initial Design Flow will be 18 GPM because it is lower than 20 GPM. Use the lower number! Still pretty simple!
Enter the “Initial Design Flow” on your Design Data Form.
This is really important! Later in step #3 of the tutorial you will determine the friction loss in your mainline. With a gravity flow system your mainline includes the pipe that brings the water to your yard from the water source! If you have a pipe that goes from the water source to a tank, you do not need to include the pipe that goes to the tank. But the pipe that goes from the tank to the yard is part of the mainline. So when you calculate the mainline friction loss you will need to calculate it for both the pipe going from the water source (or tank) to where your sprinkler system taps in to the pipe, and also the pipe from the sprinkler system tap to the valves. You then add the friction loss for both pipes together to get the “mainline friction loss”. You might want to write this down on the Design Data Form so you don’t forget!
Example: Joe Backwoods has a pipe (pipe #1) that runs from the creek way up the canyon to a storage tank on the hill above his house. From the storage tank, a second pipe (pipe #2) takes water down the hill to his house. Next to the house Joe plans to tap a new pipe (pipe #3) into the house supply pipe to take water to his new sprinkler system valves. Pipes #2 and pipe #3 are considered part of the irrigation system mainline. Joe will need to calculate the friction loss in both those pipes and add it together to find out his “mainline friction loss”. Joe isn’t worried about how to calculate the friction loss, because Joe knows that he will learn how to do it in Step #3 of the tutorial!
Do you have enough water available?
You are going to need about 20 GPM of water to irrigate 1 acre of grass with sprinklers. One acre is equal to 43,560 square feet (or 4047 square meters). So if you have a 2 acre grass yard you will need to have 40 GPM of water available in order to water it. If you have shrubs, they typically only use 1/2 as much water as grass, so 20 GPM would water 2 acres of shrubs.
If you don’t have enough water you will either need to find a larger water supply, or reduce the amount of area watered. Another option is to plant shrubs and use drip irrigation on them. With drip irrigation you only water the area the plant foliage actually covers. Therefore, if the plants only cover half the actual ground area, you only need half the water.
There are only so many hours in the day to water. The amount of water needed varies with the climate, these values are typical for hot summer areas where most sprinkler systems are installed (daily high temperatures over 90 degrees F., 32 degrees C.) These values assume you would water as much as 10 hours per day. Water more time and you can have more area irrigated.
You should probably consider installing a filter of some type on your system if the water is from a river, stream, pond, or lake. There’s a pretty good chance that all kinds of crud are in the water such as algae, sand, mineral deposits, fish, snails and clams. (No kidding!) All of these things can damage your irrigation system. For more information on filters see the irrigation filtration tutorial.
Storage Tank Capacity:
To find the capacity of an upright, round tank (measurements in inches):
radius * radius * depth * 0.01359 = gallons
example: 48 inch diameter X 48 inch high tank = 376 gallons (24 * 24 * 48 * 0.01359 = 376)
Reading this page is going to help you more than you can imagine at this point. Unless you know how to design a sprinkler system (why are you reading this?) or have training in hydraulics, it will save a lot of questions if you understand just a little of the basic principles behind irrigation system design. I’ll try to keep it light and easy on the brain cells.
STOP! If you mess this up you can ruin your pump! Read this! Most do-it-yourself sprinkler design tutorials are not suitable for rural irrigation systems that use pumps!!! Be very careful if you are also looking at one of them for guidance. The methods they use to determine water supply are little better than taking a wild guess. You’ll understand after reading this page.
If you are going to use this tutorial (and you should!) you need to use ONLY this tutorial. If not, you are going to be in big trouble. A large number of questions I get from people who are confused are caused because they are trying to mix together this tutorial with some other guide or tutorial, or maybe it was advice they got from some well-meaning, but clueless, salesman. Even many professional irrigation contractors do not understand the hydraulics of systems using pumps! Use this tutorial exclusively and save yourself a lot of grief and get a professional quality sprinkler system. Please, please, please! Thank you. You are helping save my sanity. Now on with the tutorial.
Sorry this is such a long page, but pumps are tricky. There is a lot you need to know. You can really mess up big time with a pump and an irrigation system if you do it wrong. So please be patient, read carefully, then reread it all again. Try working the examples, it helps the old brain to kick in!
None of that domesticated city water for you! You have your own pump and water source! That may be a well, river, pond, lake, or the ocean. (Ocean water? Are you growing seaweed?) Unfortunately, pumps are tricky and so you’re going to have to do a bit more work than you would if you had a “City Slicker” water supply. If you have a well, you have probably been told at some time or another that you have a “XX GPM well”. Do NOT rely on that figure! That is most likely the capacity of your well, not the output of your pump, and there is a big difference between the two. There may also be a GPM & PSI noted someplace on the pump, pump panel, literature, or the box the pump came in. Same deal. Don’t rely on these numbers, they assume optimum conditions that exist pretty much only in the pump company’s test facility. You’re going to have to do a little research, do some tests, probably get wet, and do a few calculations. I don’t recommend calling your pump and well company and asking them for the GPM of your well or water system. While some have given me a correct figure, more have given me an incorrect one! It’s not that they want to lie to you, it’s just that there are several terms here that can be easily confused. If the figure they give you is too high, your irrigation system will not work, period. If it is too low you will burn up your pump. I have written a complete tutorial on pumps and related equipment. I strongly suggest the Pump Tutorial if you would like to know more about your pump system, or if you want to know more of the reasoning behind what follows on this page. Click here to go to the Pump Tutorial.
Planning to buy a pump or install a well, but don’t have it yet? First, if you have a well, you will need to know the GPM of the well itself. That’s not how much you will pump out of it, that’s the maximum the well will provide. Your well driller should have measured this when the well was drilled, if not you will need to have the well tested by a well drilling company. They will install a temporary pump in the well to test the output. Then you need to select a random Design Flow and Design Pressure. I suggest 20 GPM per acre and 50 PSI, as those are good starting values. So if you have a 2.5 acre mini-ranch you would want to use 50 GPM at 50 PSI. Now proceed with a trial irrigation design using those values. Once you have finished the trial design, you will have discovered whether those are good values for your sprinkler system. If not, what would be? Redesign it if you have to. I know, that’s a lot of work, I agree! But, it is far easier to redesign it on paper than to try to fix it after it is installed! Once you have established a good Design Flow and Design Pressure it’s time to shop for a pump. Remember the Design Pressure is at the irrigation connection point, the pump will also need additional pressure to lift the water from the well or pond (see the pump tutorial.) After you have your pump installed and running, test it using the Wet Method below. Then create your final sprinkler design based on those results. I know this sounds like a lot of extra effort, but the result will be an almost perfectly matched pump and sprinkler system. It will be worth the effort! You should absolutely read the Pump Tutorial.
So-called “Sprinkler Pumps” and packaged pumps. Several retail hardware store chains sell what they call “sprinkler pumps”. They are also sold on a number of web sites and, of course, Ebay. At least one of them even calls their pump a “High Pressure Sprinkler Pump.” Sorry, but not by any stretch of the imagination! Typically these pumps do not provide enough water pressure for a standard sprinkler system, especially if you are on a hilly site or pumping from a water source that is more than 10 feet below the pump. (See the paragraph above for suggested pressures.) These pumps will operate small sprinkler heads on a level lot, using water from a shallow well. But few people outside of Florida have this situation. These pumps are really best suited for use as booster pumps. In general, they do not produce enough water pressure for automatic sprinkler systems. Also watch out for packaged pumps that say they are rated X GPM and X PSI on the box (insert any values for “X”.) Often these two performance figures are both the maximums possible for the pump, which may be accurate, but is also misleading. When a pump is operating at it’s maximum GPM, it will also be at the minimum PSI. There is an inverse relationship between the two values. With pumps (and this applies only to pumps) as the output pressure (PSI) goes up, the output flow (GPM) goes down. Often the figure they give you on the box is the maximum possible for each value. (Read the Pump Tutorial.) I guess what I am saying is “be very careful.” Design your sprinkler system FIRST, then buy your pump! If your calculations say you will likely need a 1.5 HP pump, and you find a 1/2 HP pump at the store that says it will do the job, be very suspicious. But most of all do not put the cart before the horse! Way too many people are contacting me and saying “Jess, I’m so thrilled, I just got a great deal on a pump on Ebay! How do I design an irrigation system for it?” They are so excited! I hate having to pour cold water on their happiness. I keep wondering how many guys (it always seems to be guys) just bought that pump on Ebay– from the last guy I heard from! Maybe this is the same pump passing from one person to the next!
Measuring Pump Output:
By the way, this looks complicated but it’s really pretty simple if you take it step-by-step! There are two ways to do this; The Dry Method and The Wet Method. I suggest you read through both of the methods, and try both of them if possible.
The Wet Method is more accurate (but only when done correctly.) The advantage to the Dry Method is that it gives you a chance to check the condition of your pump. If the Dry Method results in a much higher GPM and flow than the Wet Method, then it probably means your pump is worn out. Consider replacing your pump.
If you think you may be getting a new pump in the next 5 years, wait until you have the new pump installed before designing your sprinkler system! A new pump will likely have much better performance than the old one. If you designed your sprinkler system for the old pump then it will not work well with the new one, and may even damage the new pump!
Submersible Pumps. Many people have submersible pumps. In those cases the pump is located down inside the well, rather than on top of the well as in the diagram above. All the calculations work the same regardless of where the pump is.
First you need the horsepower of your pump. This may be stamped on the well, on the pump, on the pump panel, or your pump company should have a record of it. You may notice a GPM and PSI stamped on the pump plate also. I’ll say it again because it’s important, don’t rely on these numbers!
(A) Enter your pump horsepower on the Design Data Form.
What if you don’t have a well? If you don’t pump out of a well, substitute river, lake, pond, spring, mud-puddle, or whatever for “well” in the following procedures. In this case “water level when pump is running” is the lowest expected water level in your pond, stream, etc. (i.e.; the level the water would be in a really dry year.) You obviously also don’t have a “top of well”. So for a submersible pump when the tutorial mentions the “top of well” you would use the highest possible water level of your water source. If the pump is mounted above the water level (non-submersible), then you will need to substitute the actual pump location for “top of well” in this tutorial.
When using a non-submersible pump (any pump not below the water level) it is very important that the pump be installed as close to the water surface level as possible. Pumps are made to push water, not to pull it. The farther and higher the pump has to pull the water, the less efficient the pump will be. Some pumps work better than others in this situation, but in general expect trouble if the pump is more than 10 feet higher than the water surface. The higher your elevation is above sea level, the closer the pump needs to be to the water level. So in Denver, Colorado, the “Mile High City”, you need to have your pump very close to the water surface (or better yet, use a submersible pump.) Also, avoid long intake pipes between the water and the pump. Long intake pipes/manifolds can also hurt the pump performance. Plus a long intake pipe is more likely to have a leak in it, and a leak in the intake pipe can cause your pump to lose prime. Losing the pump prime is a real pain in the rear and if you automate your system it can cause serious damage to the pump. The bottom line here is to keep the pump as close to the water as possible.
Now you need to find out the “Dynamic Water Depth” of the water in your well. Your pump company may have a record of this, however you really should have the well “sounded” to get a new reading, especially if the well is more than 5 years old. Water levels often drop over time. As a last resort you can use the pump depth or well depth, but if you do, you may experience expensive pump problems later. Better to sound the well now, this is something your pump company can do for you and in mos cases is relatively easy and inexpensive. If you don’t have a well (you have a pond, creek, etc.,) use the lowest “dry year” water level of your water supply.
As you can see from the diagram above, the Dynamic Water Depth is the distance in feet between the top of the well and the water level in the well when the pump is running (dynamic means moving, as in the water is moving when the depth is measured.) It is important that the pump be running when this is measured. This is because when the pump runs, the water level in the well drops. The distance it drops is known as “draw-down”. The further the pump must lift the water, the more energy it takes. So as the water level gets deeper, the pump will produce less water pressure (water energy) at the outlet. That energy (water pressure) is what runs the sprinklers, so we must have an accurate measurement of it. So we need to measure the Dynamic Water Depth, not just the depth of the water table.
As you know, water flows downhill. When the pump runs it pulls water out of the well. This causes the water level to drop, and then water flows into the well from the surrounding soil. How far the water level drops depends on how hard it is for the water to move into the well from the soil. Some wells have very little draw-down, others may have 50 feet or more of draw-down. Don’t worry if you don’t understand, it will all come together later!
(B) Enter your “Dynamic Water Depth” on your Design Data Form.
Now you need to enter the elevation difference between the top of your well and the highest point in the area to be irrigated. That is, how much higher (or lower) is the highest point in the irrigated area than the top of the well. The best way to do this is to use a laser level and a tape measure. Place the laser level at the high point of the irrigation system and shoot a level beam toward the well. Then use the tape measure to measure the distance from the laser beam to the top of the well. That is the elevation difference. You may need to make several stepped measurements, or you may prefer to just make an educated guess at the elevation difference rather than try to measure it. Also, if the well is higher than the irrigated area the distance will be a negative number.
(C) Enter your elevation difference on your Design Data Form.
Add the elevation difference to the Dynamic Water Depth of the well (or subtract if it’s negative). This number (in feet) is called “elevation head” and is a measure of the height the pump must push the water to get it to your irrigation system.
(D) Enter your elevation head on your Design Data Form. B + C = D (Dynamic Water Depth + elevation difference)
One more thing needs to be factored in at this point, which is your Design Pressure. The Design Pressure is the amount of water pressure that is needed at the inlet of the irrigation system in order for the system to operate. Design Pressure is measured in PSI (pounds per square inch), but for this formula we need the pressure as measured in feet of head. To convert PSI to feet of head we simply multiply PSI times 2.31.
PSI x 2.31 = Feet Head (ft.hd.)
Well that’s all fine and dandy, but what IS our Design Pressure you ask? Good question! Guess what? “Guess” is the operative word here. Your going to need to take an educated guess at this number. For most situations I recommend that you use a Design Pressure of 50 PSI. This is a good number that works with most small to mid-size irrigation systems. For sprinkler systems with large radius sprinklers (over 35′ between sprinkler heads) you will need a higher Design Pressure. A good rule of thumb for large systems is to take the distance you would like to have between sprinkler heads in feet, and add 15 to it to get a reasonable Design Pressure. For example, if you want to put the heads 50 feet apart, you will need a design pressure of 65 PSI (50 + 15 = 65). Don’t be surprised if your system won’t pump 65 PSI, most residential pump systems aren’t designed to supply more than 50 PSI. As a side note keep in mind that higher Design Pressures result in lower flows, so the higher the pressure, the more valves you will need. I do not recommend spacing sprinkler heads farther apart than 50 feet without having a professional design the system! It gets very tricky. Even most City parks now keep the spacing between sprinklers at 55 feet or less.
(E) Enter your desired “Design Pressure (PSI)” on your Design Data form. For most of you this will be 50 PSI as discussed above. Remember this number is not written in stone! You may want to try adjusting it up and down.
Now we need the “Design Head” so multiply Design Pressure (PSI) times 2.31 to convert it to feet head. This is just a conversion from one type of pressure measurement (PSI) to another (Feet Head). Pump calculations always measure pressure in Feet Head. Example: 50 PSI x 2.31 = 115 ft.hd. (rounded down from 115.5)
(F) Multiply your Design Pressure by 2.31 and enter it as “Design Head” on your Design Data Form.
Now we put all these numbers together to get our “total pressure head”. Total pressure head is the “elevation head” plus the “design pressure head”, all in feet of head.
elevation head (ft hd) + design pressure head (ft hd) = total pressure head (ft hd)
30 ft. Dynamic Water Depth is measured in well with the pump running. The high point of yard is 10 ft. higher than top of well. 50 PSI Design Pressure, which equals 115 feet of design pressure head.
Total Pressure Head = 30 + 10 + 115 = 155 ft. hd.Another Example:
Pumping from a lake. The low water level is 20 ft. below the high water level. The lowest point of the irrigation system is 10 ft. higher than the high water level. 45 PSI Design Pressure (104 feet head).
Total Pressure Head = 20 + 10 + 104 = 134 ft. hd.Yet another Example:
For a small park, pumping from a canal. We use the canal bank as our “top of well” level. The low water level in the canal is 8 ft below the top of bank. The irrigation system is downhill from the canal, 25′ below the top of bank. 65 PSI Design Pressure needed for large turf sprinklers, which equals 150 feet of design pressure head (65 * 2.31 = 150 ft hd).
Total Pressure Head = 8 – 25 + 150 = 133 ft. hd.
(G) Calculate your “Total Pressure Head” and enter it on your Design Data Form.
Now for the flow formula:
Multiply the pump Horsepower times 2178 (a constant value, see note at bottom of this page) and then divide by the Total Pressure Head in feet.
Horsepower x 2178 / Total Pressure Head (feet) = GPM (the “Design Flow”)
So for the first example above with a 2 h.p. electric pump:
2 h.p. x 2178 / 155 ft. hd. = 28 GPM Design Flow That’s it! The GPM resulting from the above formula is your “Initial Design Flow”. You will need the Initial Design Flow and Design Pressure values later in the tutorial.
(H) Calculate your “Initial Design Flow” and enter it on your Design Data Form.
Caution: When designing a sprinkler system with a pump you want to keep the actual flow of each valve zone as close to the “Design Flow” as possible without exceeding the Design Flow. This is to keep the pump from cycling on and off as it tries to match the demand of your irrigation system. Don’t worry about valve zones now, we’ll have more on that later. Just remember this: “Valve Zone GPM must be between 80% and 100% of Design Flow”. You may want to write that down someplace.. Technical note: In order to simplify the pump formula I have factored a pump efficiency of 55% into the value of the formula constant (2178).
Pressure Up, Flow Down?!!! Wait a minute here! It seems like what this formula says is that if the pressure goes down the flow goes up! That just doesn’t make sense. What gives? O.K., by popular demand, here’s an answer to this little dilemma. It’s one of those obscure, hard to understand hydraulic principles I was yapping about earlier. Sit back. Grab a nice soothing cup of tea or whatever. Put on some soft, relaxing background music. Ready? Here we go… I know it doesn’t SOUND logical, but believe me it IS correct. You’re thinking if more pressure is added then more water will be moved, which is true, but your talking about ADDING pressure, not using the AVAILABLE pressure! And that is the key to the problem. Remember we are measuring your AVAILABLE pressure and flow, based on the current conditions at your house (or whatever). If we were planning to add a big pumping system then we would use a different approach. So the correct way of looking at it is “how much water can we move with the pressure that your existing pump can supply?” It takes energy to move water, and the water pressure is the energy that is used. But as the water is moved, the energy is used up. So the water pressure goes down. And as more water is moved, even more of the existing pressure is consumed moving it. So as the flow (GPM) of the water increases, the pressure (PSI) of the water must decrease! (Because the pressure is used up moving the water.) Does that make sense? Well even if you don’t get it, that’s O.K. It takes most engineering students 2-3 months of college level class work before they fully understand hydraulics, so don’t feel bad if it still doesn’t make sense. You’ll just have to believe me that it’s correct (and don’t worry, it is!).
Wet Method (Also called the “Bucket Method”)
This is the most accurate way to test your pump. BUT… Before we start into this I need to warn you that you must follow the instructions below exactly.Do not skip any steps, do not shortcut. If you do not follow these steps exactly you will get a false reading, your sprinkler design will not work, and you probably will destroy your pump! Understand?
Sprinkler systems need pressurized water to operate. Without the pressure, the water doesn’t shoot out of the sprinklers! Think of water pressure as the “energy” that moves the water. Just measuring the water flow with a bucket is not good enough, we must also measure the water pressure at the same time, as we need that pressure to make the sprinklers spray water. If you had a city water supply we would measure the “Static Water Pressure”. This is the pressure when the water isn’t moving. The amount of water available on a city water system is determined by the size of the pipe supplying the water. But for a pumped system the amount of water available is determined by the size of the pump. So for a pump we must measure the “Dynamic Water Pressure”. Dynamic water pressure is the pressure of moving water. Dynamic pressure will always be lower than static pressure. This is because when the water is moving friction is created with the edges of the pipe. This friction consumes energy (remember, pressure is energy) so the pressure drops. The faster the water moves, the more friction, so the pressure is reduced even more. When pumping water there is an inverse relationship between flow and pressure. So if you want to get more pressure, you will also get less water flow. If you just turn on a faucet and measure the flow into a bucket the pressure falls to zero (the water just falls into the bucket, therefore no water pressure). That results in a higher than normal flow (lower pressure = higher flow). To make matters worse, most people measure the flow from a standard faucet. The small size of the faucet restricts the flow, adding more error to the measurement. If you’re lucky the errors balance each other out. But who knows? Add in a little sloppy measuring, and the results can be off by 20% or more. That can be enough to cause your pump to cycle, which will result in pump failure. Replacing pumps is a major expense, so let’s do this thing right. It takes more time and effort, but it will be worth it. Need to know what size your pipe is? How to find the size of a pipe.
Pump and Pressure Tank Example #1:
The light green colors are the new pipes added for the test. Later you can use this new pipe for the supply pipe (mainline) for your sprinkler system supply tap, so installing this isn’t a waste of money. When the pipe from the pump goes into the tank and then another pipe comes out and goes to the house you should make your tap after the tank as shown. Note that the pressure tank may not be near the pump, especially in cold winter areas where the tank is often installed in the house basement. The new piping can be vertical if you wish, and you can add ells to the last section to get the pipe over the top of the bucket. The 8″ straight lengths of pipe before and after the pressure gauge are important, they must be 8″ long and there can’t be any ells in these sections. The purpose is to avoid creating turbulence in the water that could affect the pressure gauge accuracy.
Pump and Pressure Tank Example #2:
When the pressure tank only has a single pipe going into it you can tap the pipe anywhere. You can tap it between the pump and pressure tank as shown, or after the pressure tank. Most pressure tanks are set up this way. Note that the pressure tank may not be near the pump, especially in cold winter areas where the tank is often installed in the house basement. The new piping can be vertical if you wish, and you can add ells to the last section to get the pipe over the top of the bucket. The 8″ straight lengths of pipe before and after the pressure gauge are important, they must be 8″ long and there can’t be any ells in these sections. The purpose is to avoid creating turbulence in the water that could affect the pressure gauge accuracy.
Follow the instructions below exactly! Please read the sentence above again.
1. Select the location where you will connect the sprinkler system into your water system (your “tap location”). See the pump and pressure tank example diagrams above. In some (very few) pump systems you must tap the pipe after the pressure tank as in Example #1. However, most systems are like Example #2, so you can tap into the water supply line anywhere you want. In this case it is often best to tap as close as possible to the pump. This will usually give you a higher pressure, which means a better sprinkler system (and often less expensive, too!) In some cases you may want to connect your new irrigation system into an existing pipe somewhere a considerable distance away from the pump, such as a faucet near a garden. This is fine, go ahead and try it. The problem is that often the existing pipe is not large enough. You may find that you don’t get a very high water pressure due to the small pipe. If this happens you can confirm the problem by making another tap near the pump and testing there also. If you get a much higher pressure and flow when you test near the pump, then the existing pipe is too small.
2. If there is already an outlet on the pipe at your desired tap location you may use it for the test, provided the outlet is the same size as the pipe coming from the pump. If there is not already an outlet you will need to cut the pipe and install one as follows. Measure the size of the pipe. Go to the hardware store and purchase a compression tee that will fit the pipe. Have the sales person show you how it works. I suggest using a metal compression tee rather than plastic. The side outlet of the compression tee should be the same size as the pipe you are tapping into. At your tap location, cut a short section out of the pipe out and install the compression tee.
Note, sometimes it is necessary to brace the compression tee in place to prevent it from moving and slipping off the pipe. In some situations compression tees will not work. In that case you may need to install a threaded or glue in place (pvc pipe only) tee. If you have the time and skill to install a threaded or glued tee, that is always a better option than a compression tee.
3. Install the parts shown in green as per the Wet Method Pump Output Test sample drawings above as follows:
Start with an 8″ long pipe section installed on the (compression) tee outlet, then another tee with a 0-100 PSI pressure gauge on it, then another 8″ long pipe section, then a ball valve, then add a temporary PVC pipe (maximum of 4 feet of pipe with 3 ells) so that you can fill a 5 gallon bucket to measure the water flow. All the pipes and the valve should be the same size as the pipe you cut to make the tap. Do not use a garden hose, it will restrict the flow and give you a false low flow reading! I strongly suggest using metal pipe and fittings between the tap and the ball valve. I also suggest using a brass (or bronze) ball valve. This ball valve will become the shut-off valve for your future sprinkler system. The last pipe section going to the bucket after the ball valve is temporary and can be plastic. See the example drawings above. The rest of this test process is going to dump a lot of water on the ground, so now is a good time to figure out where that water will go, before you’re up to your knees in mud!
4. Get a “5 gallon bucket”. Since most 5 gallon buckets actually hold more than 5 gallons of water you probably will need to “calibrate” it and mark the actual 5 gallon volume level on the side of the bucket. Fill it with 5 gallons of water using a accurate measuring container to measure the water, then mark the water level on the bucket with a marking pen so you can easily see it. Empty the bucket.
5. Open the ball valve and allow the water to flow freely from it for at least 5 minutes so the flow from the pump can stabilize. ( If your pump is manually controlled you will have to manually start it.) Assuming you have a pressure controlled pump like most are, the pump should start by itself and run continuously during this time.
If the pump shuts off by itself when running with your test outlet full open you have an unusual problem, probably too much restriction in the piping. First check to see if there is any kind of restriction in the pipe (I’ve found rocks, toy cars, rags, rats, fish, roots, etc. in pipes). If not, the pipe from your well may be too small. Best to call a pump company for help at this point as something is seriously wrong with the pumping system.
6. With the pump running, watch the PSI reading on the pressure gauge, and slowly start closing the ball valve until the pump shuts off. The water pressure shown on the gauge will increase as you close the valve. (As the flow from the pump is reduced the pump produces more pressure.) Make a mental note of the pressure when the pump shut off.
7. Reopen the ball valve and wait for the pump to start again. Now slowly close the ball valve again until you find the point at which you get the highest possible pressure reading on the gauge without the pump shutting off. When you find this “balance point” the pump should run continuously and the pressure should remain more or less constant. You will need to close the valve a little, then wait, then close it some more to do this.
What you are determining is the exact point where your pump produces the highest possible combination of pressure and water flow. Do not turn off the pump or adjust the ball valve from now until you finish the rest of the steps! In order to tell when the pump shuts off you may need someone to help out by standing close to the pump and signaling to you. The water coming out of the valve may be loud enough that you can’t hear the pump running. If you have a submersible pump it will be even harder to hear. Try removing one of the plugs in the top of the well so you can hear better. Another method is to see if you can feel the vibration of the water running in the pipe where it exits the well. Water will not be flowing through this pipe when the pump is off.
If you absolutely can’t tell if the pump is running you will need to just watch the flow and pressure. Adjust the valve until you find a flow where the pressure stays constant for at least 15 minutes.
If you don’t have a pressure switch on your pump you still use the same method for the test. But instead of listening for the pump to shut off you will just have to play with the flow until you reach a good balance between flow and pressure. You will notice as you close the valve that there is a point where you have to severely reduce the flow to make the pressure go higher. Keep your pressure below this level, it is not good for the pump to restrict the flow too much.
The pressure reading is going to be your design pressure. If it is too low, you may have problems with your sprinkler design. For most situations I recommend that you use a Design Pressure of 50 PSI. This is a good number that works with most small to mid-size irrigation systems. For sprinkler systems with large radius sprinklers (over 35′ between sprinkler heads) you will need a higher Design Pressure. A good rule of thumb for large systems is to take the distance you would like to have between sprinkler heads in feet, and add 15 to it to get a reasonable Design Pressure. For example, if you want to put the heads 50 feet apart, you will need a design pressure of 65 PSI (50 + 15 = 65). Don’t be surprised if your system won’t pump 65 PSI, most residential pump systems aren’t designed to supply more than 50 PSI. As a side note keep in mind that higher Design Pressures result in lower flows, so the higher the pressure, the more valves you will need. I do not recommend spacing sprinkler heads farther apart than 50 feet without having a professional design the system! It gets very tricky. Even most City parks now keep the spacing between sprinklers at 55 feet or less.
Most pumps have a pressure switch on them that turns the pump on and off at preset pressures. Typical settings are 35 PSI on and 45 PSI off. It works just like the heater and thermostat in your house do, only it measures water pressure rather than temperature. When you open the valve, the water flows out and this causes the water pressure to drop. When it reaches the preset “on” pressure the pump turns on. As you close the valve the pressure climbs, when it reaches the preset “off” pressure the pump shuts off. This creates a problem if you want to get 50 PSI and the pump turns off at 45 PSI! Fortunately, the pressure at which the pump turns on and off can be adjusted. So if your pump is turning off at less than 50 PSI you may want to have the settings adjusted. You may be able to increase the off setting by 5 PSI or so. Sometimes this requires the installation of a new pressure switch on the pump, most can only be adjusted within a limited range. If you need to replace the pressure switch, have a pump professional do it. You can damage the pump if you use a switch with a pressure range that is too high. Your pump may not be designed to pump higher pressures! So how do you adjust the pressure setting? Somewhere on the piping, usually near the pressure tank, there is a tee in the pipe and a small box is sitting on a short pipe above the tee. The box has electrical conduit running to it. This is the pressure sensor. It has an adjustment screw inside it the box cover. I can’t tell you much more than that, depending on the model the location of the screw will vary. You may be able to find instructions for the pressure switch online by searching for the manufacturer’s website. Newer pumps often have solid state pressure sensing. Depending on the model you may be able to change the settings using the keyboard. Other models do not have a keyboard, they must be hooked up to a programming device to change the settings. You will need to call your pump company for help.
A. Write down the pressure gauge reading on the line “Design Pressure (PSI)” on your Design Data form.
8. Now measure the flow coming out of the pipe without adjusting the ball valve. The pressure gauge must stay at the “Design Pressure” and the pump must continue running while you measure the flow. Put your 5 gallon bucket under the flow and time how many seconds it takes to fill the bucket to the 5 gallon mark. Repeat this 3 times to make sure the the results are accurate (all three measurements should be about the same). Divide 300 by the number of seconds it takes to fill 5 gallons into the bucket to get the GPM. (300 / seconds to fill 5 gallon bucket = GPM) Example: 10 seconds to fill the 5 gallon bucket, therefore 300 divided by 10 seconds equals 30 GPM.
B. Write down the flow (GPM) you measure on the line “Initial Design Flow” on your Design Data Form.
You’re done measuring. You can close the valve now and shut off the pump if it is locked on. Leave the ball valve in place, you will connect your new sprinkler system to it.
A Few Other Important Items to Note
Caution: When designing a sprinkler system with a pump you want to keep the actual flow of each valve zone as close to the “Design Flow” as possible without exceeding the Design Flow. This is to keep the pump from cycling on and off as it tries to match the demand of your irrigation system. Don’t worry about valve zones now, we’ll have more on that later. Just remember this: “Valve Zone GPM must be between 80% and 100% of Design Flow”. You may want to write that down someplace.
Do you have enough water available from your pump?
You are going to need about 20 GPM of water to irrigate 1 acre of grass with sprinklers. One acre is equal to 43,560 square feet (or 4047 square meters). So if you have a 2 acre grass yard you will need to have 40 GPM of water available in order to water it. If you have shrubs, they typically only use 1/2 as much water as grass, so 20 GPM would water 2 acres of shrubs. If you don’t have enough water you will either need to find a larger water supply, or reduce the amount of area watered. Another option is to plant shrubs and use drip irrigation on them. With drip irrigation you only water the area the plant foliage actually covers. Therefore, if the plants only cover half the actual ground area, you only need half the water.
There are only so many hours in the day to water. The amount of water needed varies with the climate, these values are typical for hot summer areas where most sprinkler systems are installed (daily high temperatures over 90 degrees F., 32 degrees C.) These values assume you would water as much as 10 hours per day. Water more time and you can have more area irrigated.
Minimum pipe size:
If the pipe between the pump and the tap point for the irrigation system is longer than 10 feet (for submersible pumps measure from where the pipe exits the well) then the pipe must be as large or larger than the following:
Initial Design Flow
Minimum Pipe Size
0 – 5 GPM
5 – 15 GPM
15 – 30 GPM
30 – 40 GPM
40 – 70 GPM
70 – 100 GPM
100 – 160 GPM
If the pipe is smaller than the above minimum sizes you will need to replace it to avoid the possibility of water hammer which can damage your pump, pressure tank, and household plumbing, not to mention the sprinkler system. If your design pressure is over 50 PSI use one size larger pipe than what is show. Example- 55 PSI design pressure and 35 GPM Design Flow require a 2″ pipe (one size larger than chart says because design pressure is over 50 PSI).
Lots more on pumps…
I strongly suggest you take a look at my Irrigation Pumping Systems Tutorial. There’s a lot more information on pumps, pump controls, and pumping from wells, lakes, rivers, etc. in the Irrigation Pumping Systems Tutorial.
In this step you will make some preliminary selections of the equipment such as sprinkler heads, valves and more. When selecting your sprinkler equipment we need to also find out how much pressure loss each item creates. The amount of pressure loss may require that you reconsider one product over another. Keep reading and it will become clearer.
Like all other mechanical systems an irrigation system consumes energy when it operates. The irrigation system uses energy in the form of water pressure which, as we noted earlier, we will be measuring in PSI (pounds per square inch). Each component in the irrigation system that the water passes through consumes a little bit of that water pressure. A bit like a car uses more fuel for each mile it goes. If we run out of water pressure before the water makes it through the system, then the irrigation system will not work. So we need to calculate how much pressure will be lost in each component of the irrigation system. To start we will make some educated guesses, which are then confirmed and adjusted by using a trial and error process. Don’t worry, it’s easy to do…
Below is a Pressure Loss Table that lists items that you MAY need to factor into your pressure loss calculations. Some of the items may not be necessary in some situations. The tutorial has a page for each of the items that will tell you everything you need to know. I will explain to you all the pros and cons of the various product types available. For the more complex choices like backflow preventers, I will lead you through a series of simple questions that will guide you toward the best solution for your specific irrigation system. Then you will pick your actual equipment and enter the associated pressure loss value into the Pressure Loss Table on your Design Data Form.
Near the bottom half of your Design Data Form there is a copy of the Pressure Loss Table below.
Hopefully you picked up a copy of the Design Data Form earlier in the tutorial. If not, please go back to the appropriate page for your water supply source below so you can figure out the correct values for available GPM, PSI and get the form:
You’ll refer back to these values several times throughout the design process and you may need to change them a few times, so use a pencil so you can erase and rewrite values! If you have bad handwriting skills like me, you may wish to write a bit neater than normal so you can read it later! There’s nothing worse than having to go back and recalculate your data because you can’t read your own handwriting. Believe me, I’ve had to do it way too many times! If an item on the table doesn’t apply (for example, you don’t have a water meter) just enter n/a and a pressure loss value of 0 for that item.
OK, here’s a typical Pressure Loss Table.
Pressure Loss Table
Item (links jump to a page with details on each item)
Don’t panic! The next few pages of the tutorial goes through each item on this table and helps you to figure out the pressure losses to enter on each line of the table. If you’ve used the tutorial before and already know a lot of this, the links in the table above will allow you to jump ahead in the tutorial to the page where the details on that item are located. For most people you will want to just keep reading the pages in order.
Pressure Regulators & Pressure Reducers
Before we continue on we need to address pressure regulators/reducers. A pressure reducer is another name used for pressure regulators. I’m going to use the name “pressure regulator” to avoid confusion. A pressure regulator is a special valve that reduces the water pressure to a set level and keeps it at that level. Some homes have these pressure regulators installed on the water supply, which can impact the values used in the Pressure Loss Table. If you have a municipal water supply, you already learned a little about pressure regulators on the City Slicker Water page of the tutorial. Back on that page you should have discovered if you have a pressure regulator and, if you do, you also decided if you would tap into your water supply before or after that pressure regulator.
If you have a pressure regulator on your house then you get to take a little shortcut. On your pressure loss table you get to ignore the pressure loss for everything upstream of the pressure regulator.
Installing a Pressure Regulator
If you are planning to install a new pressure regulator be aware that there are two types sold. The one you want to use on your house will be made of bronze or brass, have a pressure adjustment screw so you can set the downstream pressure you want, and generally are pretty expensive. If you need one for a sprinkler system I suggest it also be this more expensive type. There are also cheaper models that use a different principle to work, these cheaper ones are often used on drip irrigation systems. They are not adjustable, and not nearly as accurate and will often allow a damaging pressure surge to pass through them. They typically are barrel-shaped and constructed of plastic. They will not have a adjustment screw or knob on them.
Before you decide to take a shortcut and install a pressure regulator right before the valves so you can ignore pressure loss in the mainline, consider that the higher pressure may not be good for those upstream components. Generally I try to avoid pressures over 100 PSI in any portion of my sprinkler systems. I strongly recommend that you do likewise. Also remember that maximum water velocities also still apply to the mainline pipes, so you will still have to do the size calculations for the mainline.
When placing a pressure regulator on an irrigation system I normally install it right after my main irrigation system shut-off valve at the place where I tapped into the water supply. Thus I have:
connection to water supply –> emergency shut-off valve –> pressure regulator –> irrigation system.
Don’t forget the pressure setting of a pressure regulator must always be at least 15 PSI lower than the incoming pressure. So if the incoming pressure is 80 PSI the pressure regulator must be set at 65 PSI or less. Otherwise the pressure regulator will not work accurately and may allow damaging pressure surges to pass through it. To restate this another way, the pressure regulator must reduce the pressure by 15 PSI or more for it to work accurately and reliably.
You may or may not have a water meter. If you buy your water from a water company or municipal water district you probably have a meter. If your water comes from a well, lake, or stream you probably don’t have a meter. The water meter measures how much water you use, that way the water company can charge you for the amount you use. Even if you get your water from a water provider you may not have a water meter, I didn’t have one at a couple of the homes I’ve owned (water was provided for a flat monthly fee regardless of how much was used.) If you do have a meter where should you look for it? In warm weather climates it will most likely be located near where your water supply taps into the water company’s pipes. This is usually right next to the street curb, or perhaps adjacent to an alley behind your home. In climates with extreme cold weather the meter may be under the house in the crawl space, but in most cases it is inside the basement. Many newer meters have electronic features for remote reading, they send your water usage information to the water company via wires or radio signals. Many of these new electronic models are actually flow sensors rather than traditional meters. See the section on flow sensors below.
Just as a side note, most water meters measure cubic feet of water. Cubic feet is the measurement unit that water providers like to use. A cubic foot of water is equal to 7.48 gallons. Do not confuse cubic feet with acre feet. Both are measurements of water quantity, but they are not the same thing. An acre-foot is a whoping 325,900 gallons!
Flow Sensors (optional)
Some people install their own water metering device on the irrigation system main supply pipe so they can monitor just the irrigation water usage. A flow sensor rather than a water meters is used for this. The difference between the two is that a typical water meter measures only the amount of water used, flow sensors measure the rate of flow. This allows them to monitor how much flow the irrigation system is using at any given moment. The flow sensor typically creates an electronic pulse when a given amount of water has passed through it, for example a cubic foot of water. The flow sensor connects up to the irrigation controller that is used to turn on and off the irrigation system. Some higher-end models of irrigation controllers have the ability to monitor the number of pulses from the sensor and use the data to determine how much water is flowing at the moment, as well as the total amount of water used per irrigation cycle. Using this information the controller can evaluate the irrigation system performance and respond to it. For example the controller might detect that the flow is higher than normal, indicating a leak in the irrigation system, or maybe a broken sprinkler head. Likewise a flow that is lower than expected might indicate a valve did not open when it was supposed to. The controller then sounds an alarm, or may shut off the water to limit damage from the leak. Flow sensors and controllers that monitor flow are features that are common on many larger irrigation systems, like parks and golf courses. Now, as the price of the equipment is rapidly dropping and water conservation is becoming an issue in more places, homeowners are starting to implement these optional flow sensing features as well. Controllers that have this monitoring feature are called “Smart Controllers”. Note that not all Smart Controllers have this monitoring feature. For more information see the article on Smart Controllers.
If the meter is buried in a box, be careful when you open the box. Over the years I’ve encountered just about every creepy thing one can imagine in those boxes! Turtles, rats, snakes, various dead things. Ants and spiders are most common. It’s not a bad idea to be prepared to jump back, and maybe have a can of bug killer handy when opening a underground box. Once you find the meter you will likely need to clean it off so you can clearly see it. The meter should have a size stamped on it, if not, sometimes the meter size is shown on your water bill. If all else fails, call your water company and ask them for the meter size, it should be in their water billing information. The pressure loss (PSI Loss) for water meters is based on the meter size and the flow rate. If you know the brand of the water meter you can probably find a table on the manufacturer’s website that tells you the pressure loss for the meter size at various rates of flow. If not, the charts below should be close enough.
The charts below give typical pressure losses for various meter sizes and flow rates. If your meter is a combination of two sizes (like 5/8 x 3/4) use the chart for the smaller size. These dual-size meters are made by taking a small meter and putting a larger size inlet and outlet on it. So it is really the smaller size meter. For flow sensors you will need to contact the sensor manufacturer to find out how much pressure loss to expect in your unit. Flow sensor losses are generally less than those for a standard water meter, so if you can’t find a manufacturer’s flow loss table, in most cases you can safely use the values in the water meter tables below for flow sensors.
Find your meter size below, then use your “Initial Design Flow” (from your Design Data Form) to find the PSI loss. Enter the PSI loss from the table below on the water meter line of the Pressure Loss Table. If you don’t have a water meter just enter 0 on the table. If you modify the Initial Design Flow later you should come back and change the water meter/flow sensor PSI Loss values as well. (This will be true of all your PSI Losses in the Pressure Loss Table that are based on flow. If you change the Design Flow for your system you will need to update the PSI Loss values. There is a bit of trial and error to the irrigation design method as you attempt to find that “sweet spot” that balances pressure vs. flow to give the optimum performance.)
1 PSI loss
2 PSI loss
3 PSI loss
4.5 PSI loss
6 PSI loss
8.3 PSI loss
Don’t exceed 15 GPM
0.5 PSI loss
1 PSI loss
2 PSI loss
3 PSI loss
5 PSI loss
6.5 PSI loss
Don’t exceed 20 GPM
0.5 PSI loss
1 PSI loss
2 PSI loss
3 PSI loss
4 PSI loss
5 PSI loss
6 PSI loss
7 PSI loss
Don’t exceed 34 GPM
1 1/4″ meter: (This is not a standard water meter size. If you have one it is probably a 1″ meter modified to have a 1 1/4″ inlet and outlet. But, then again, it might be a 1 1/2″ modified to 1 1/4″. Not very helpful? Unless you are reasonably sure by looking at it that it is a 1 1/2″, you should assume it is 1″.)
1 1/2″ meter
0.5 PSI loss
1 PSI loss
2 PSI loss
3 PSI loss
4 PSI loss
5 PSI loss
6 PSI loss
7 PSI loss
Don’t exceed 60 GPM
1 PSI loss
2 PSI loss
3 PSI loss
4 PSI loss
5 PSI loss
6 PSI loss
8 PSI loss
Contact manufacturer for larger size meters.
That wasn’t hard, was it? You’re gonna fly through this!
Backflow Preventer: A device that allows water to go through it in one direction, but prevents it from going backwards in the opposite direction.
A backflow preventer is like a one-way gate for water. Most backflow preventers are used to keep unsafe water from reversing flow and entering the clean water supply. Backflow preventers can be as simple as a single check valve that closes when water flow reverses. Using a simple check valve as a backflow preventer might be considered the equivalent of a turnstile at a store entrance, it is not very reliable, even a small amount of effort will overcome it. A more elaborate backflow preventer can be a complicated device that consists of multiple check valves, water release valves, air vents, and/or systems to allow it to be tested to assure it is working properly. This kind of backflow preventer might be the equivalent of an airport exit security checkpoint with one-way gates and a armed guard.
Here are links to the backflow preventer related topics below in case you come back and want to reread something. (Sorry this page is so long, it’s a complex topic and there are a lot of options available to you!)
Backflow Preventer definition: A device that allows water to go through it in one direction, but prevents it from going backwards in the opposite direction.
A backflow preventer is like a one-way gate for water. Most backflow preventers are used to keep unsafe water from reversing flow and entering the clean water supply. Backflow preventers can be as simple as a single check valve that closes when water flow reverses. Using a simple check valve as a backflow preventer might be considered the equivalent of a turnstile at a store entrance, it is not very reliable, even a small amount of effort will overcome it. A more elaborate backflow preventer can be a complicated device that consists of multiple check valves, water release valves, air vents, and/or systems to allow it to be tested to assure it is working properly. This kind of backflow preventer might be the equivalent of an airport security checkpoint with one-way gates and an armed guard.
You should have a backflow preventer on your irrigation system if your water comes from a “potable” (drinkable) source (see next paragraph.) If your irrigation water source is considered potable, then in most places it is illegal to not have the proper local authority-approved type of backflow preventer on your irrigation system. If your water source is non-potable, you generally are not required by law to use a backflow preventer (but not always, some jurisdiction even require them for non-potable water like recycled, reclaimed, and gray water sources.)
There are many types of backflow preventers. Almost everywhere the local authorities will dictate that certain types of backflow preventers may NOT be used with irrigation systems within their jurisdiction. In some cases, the authorities will dictate the exact type of backflow preventer you MUST use. You may hear or see the term “Cross-Connection Control“, this essentially is referring to backflow prevention. A cross connection is a connection between a drinking water supply and a source of pollution or contamination.
What’s potable water? Definition: potable water means the water is suitable for drinking. Depending on local law, that may include drinking water for animals. If you would be willing to drink it without treatment, then it is probably going to be considered potable. Non-potable water is water that is not suitable for drinking. (Once water enters into your irrigation system it is considered to be non-potable, more on that later.) Examples of water sources that are often considered non-potable are lake and pond water, water from streams, and well water from a contaminated aquifer that is not suitable for drinking. Most other wells do require a backflow preventer, even if the well doesn’t provide drinking water. This is to protect the aquifer the well takes the water from, because even if you don’t get drinking water from the well, your neighbors may get drinking water from the same underground aquifer. If you plan to apply fertilizers or pesticides using your irrigation system, then in most cases you must have a backflow preventer- regardless of the water source. Nobody wants those chemicals going into lakes, streams or the water table!
Why do you need a backflow preventer? All irrigation systems contain a chemical called dihydrogen monoxide. This odorless, tasteless chemical is known to be deadly if inhaled and has killed millions of people. OK, before you flame me, dihydrogen monoxide is, of course, the scientific name for ordinary water (h2o). Which points out that you have to be really careful about what you read and believe on the Internet. Unfortunately when it comes to backflow preventers there is a lot of questionable, and sometimes completely wrong, information. So what’s the deal with backflow prevention? Is it really necessary? The answer is yes!
Your landscape has all kinds of nasty things in it that will make you sick or worse if you drink them. Thus irrigation water is officially considered a contaminant (creates a health hazard) rather than just a pollutant (is objectionable in color or odor). What’s in irrigation water? How about toxic chemicals (fertilizers, pesticides, etc.) and animal waste? (Not that I want to gross you out, but every day millions of dogs lift their legs in a fond salute to their favorite sprinkler head!) These things can and WILL come back up your irrigation pipes and into your drinking water if you don’t stop them. If you have a well, they can go down your well and into everyone else drinking water. If you are on a community water system they could go back up into the pipes and poison your neighbors. The valves that turn on and off your irrigation system are not sufficient to stop backflow. The purpose of the backflow preventer is to protect you when the valve breaks or leaks, which all valves will do eventually. Saving a little money by skipping the backflow preventer will not seem so smart after you spend a small fortune on hospital bills (or funeral expenses) for a poisoned family member or pet!
Now wait a minute, some people say, doesn’t the water pressure in the water system keep the irrigation water from going backwards? Yes, most of the time it does. But there are times when the water pressure drops in the supply system, and this is when the backflow occurs. No, it is not a frequent occurrence. But it does happen more often than you think, often at night when you don’t notice the water was off for a few minutes. Such as when the water company has to shut off the water to repair a water pipe, or hook up a new pipe. This makes construction projects easily the most common cause of backflow problems. Fire fighting is another common cause of backflow. Fire trucks use huge pumps to suck the water out of the fire hydrants. This often causes the water pressure in the surrounding areas to drop, and backflow will occur in the surrounding neighborhoods.
You can do a quick experiment yourself and create backflow in your home pipes. Simply tun off the water valve leading to your house. Next have someone turn on a faucet. Now turn on a different faucet that is higher than the first. You will hear air being sucked into the higher faucet. You just created backflow in your house piping. Pretty easy, wasn’t it?
Another common argument against the need for backflow preventers is that if all the valves are closed the water can’t go backwards through them. So the valves should prevent backflow. The obvious problem with this is that if the backflow occurs at a time when the valve is open, like when the sprinklers are on, the valve will not stop backflow! But even when the valve is closed it may not prevent backflow. A standard manually operated valve should stop backflow when it is closed– if the valve if fully closed, has good seals, and does not leak. However most of the automatic valves, such as the electric solenoid valves used for irrigation systems, will not stop backflow even when “off” and fully closed. This is because these solenoid valves are directional in design. If you look on the valve you will see that it has an arrow on it showing the flow direction. If the flow is reversed, the valve will often open slightly (that’s why the valve has the arrow on it- to warn you not to install it backwards!) Thus when backflow occurs and the flow direction reverses, an automatic valve will not stop the backward flow.
Backflow Preventer Costs
Prices vary dependent on your situation, but as a general rule the costs of backflow preventers fall into the order that follows, from most expensive to least expensive. (Don’t panic, descriptions of each of the types are further down this page. Knowing prices will help with selecting which type to use.)
$$$$ Reduced Pressure Type Backflow Preventer (RP)
$$$ Double Check Type Backflow Preventer (DC)
$$ Pressure Vacuum Breaker (PVB)
$ Anti-Siphon Valve (ASV) -up to about 6 valves*
*Generally a PVB with standard globe valves becomes less expensive than anti-siphon valves when you have a lot of valves on the system.
How to Select a Backflow Preventer
There are several types of backflow preventers available, so let’s take a look at your options. Always check with the local water provider or government building department (whomever issues building permits) to be sure that the backflow preventer you plan to use is legal to use in your area. Regulations vary depending on location. Backflow preventers are expensive, so you do not want to have to tear it out and install a different one!!!
The following questions will help you decide which type to use. Each type is described in detail further down on this page, a link on the name will take you to the description.
WARNING: Be sure to read the description and related warnings about the type backflow preventer carefully before deciding which type to use. Make sure your choice is legal in your community!
Is this a commercial or a single family residential site?
Commercial: (This includes ANY business property, including apartment complexes and condominiums.) Use a Reduced Pressure Type Backflow Preventer. This is the industry standard. For commercial projects you don’t take chances, you use a Reduced Pressure Type because it provides the highest level of protection. If something goes wrong a commercial property owner is likely to be held to a very high standard. An hour of your attorney’s time in court costs you more than any backflow preventer!
Single Family Residential: Continue to the next question.
Do you plan to use fertigation, apply fertilizer, pesticides (such as for insect control), or apply anything other than pure water using your irrigation system? This includes products labeled as “organic”, “natural”, and “safe”. This also includes the “safe” mosquito control products applied by misters and sprinklers. Remember all these products are concentrated in the irrigation system water, so while they may be safe when dispersed into the air, they can be much more dangerous when concentrated in the water in the pipes.
Do you want the backflow preventer to be installed below ground in a valve box?
Yes: Consider a Double Check Type Backflow Preventer, it is the only type that can be installed in a box below ground. Note: other types may sometimes be installed in a large vault with unblockable drainage. (For example, you can generally put a Reduced Pressure Type Backflow Preventer in a large basement.)
No: Continue to the next question.
Is it possible to install the backflow preventer in a location where it will be at least 6 inches (150mm) above all of the sprinkler heads or drip emitters/drippers?
Following is a list of the various types of backflow preventers. All of the following backflow preventer types are available in all sizes. You may need to contact a specialty irrigation store or plumbing supplier to obtain some of these backflow preventers.
A “control valve” is the valve that is used to turn on and off a group of sprinklers or a drip system. Typically an irrigation system will have several control valves, each turning on the irrigation in a different area of the yard. A control valve may be automatic (turned on and off by a timer) or it may be manual (turned on and off by hand.)
Atmospheric Vacuum Breaker. The atmospheric vacuum breaker (AVB) is the least expensive backflow preventer. The AVB is installed on the pipe right after the control valve. If you use AVBs for backflow prevention you must install one AVB after EVERY control valve, no exceptions. It must be installed at least 6 inches (150mm) higher than the highest sprinkler head, bubbler, or drip emitter outlet that is turned on and off by that control valve (some AVB manufacturers, and in some areas local officials, require that AVBs be installed 12 inches (300mm) higher than the sprinkler heads). It may not be installed in any location where it might ever be submerged under water, like in a underground box. As a general rule AVBs are not economically practical if you have more than 6 or so valves. In this case you would want to consider a pressure vacuum breaker. Some municipalities do not allow the use of AVBs. Most people use a anti-siphon valve (see next item) rather than a valve and a separate AVB. An anti-siphon valve is generally less expensive and less work to install. If you install any valves, of any type, on the pipes downstream of the AVB, the AVB will not work! The downstream valve creates “back pressure” on the AVB which causes the vent in it to jam in the closed position. If this vent can’t open, the AVB will not prevent backflow. (Exception: drain valves for winterizing the system are OK and may be installed after an AVB valve, provided they are configured only to drain the pipe. A properly installed drain valve should not create backpressure on the AVB.)
Anti-Siphon Valve. A anti-siphon valve is a manual or automatic control valve with a built-in atmospheric vacuum breaker. Like the AVB it must be installed 6 inches (150mm) higher than the highest sprinkler head or drip emitter outlet. If you install any valves, of any type, on the pipes downstream of the anti-siphon valve, the anti-siphon valve will not work! The downstream valve creates “back pressure” on the anti-siphon valve which causes the vent in it to jam in the closed position. If this vent can’t open, the anti-siphon valve will not prevent backflow. It may not be installed in any location where it might ever be submerged under water. (Exception: drain valves for winterizing the system are OK and may be installed after an anti-siphon valve, provided they are configured only to drain the pipe. A properly installed drain valve should not create backpressure on the A/S valve.)
Anti-siphon valves are the most common type of backflow preventer used on residential irrigation systems, primarily because they are simple and inexpensive. Some municipalities do not allow the use of anti-siphon valves, so it is best to check with the water company first. Generally you would install the anti-siphon valves in one or more groups, at the highest point in the area to be irrigated. A mainline pipe is run to the anti-siphon valve location(s) from the water source. Pipes then extend from each anti-siphon valve to the sprinklers or emitter tubes. Because anti-siphon valves must be installed at least 6 inches (150mm) above ground, it is a good idea to put a small planting of shrubs around them to help hide them from view. They are not particularly attractive! Water may come out of the anti-siphon valve periodically, so make sure you install them someplace where a little spilled water will not be a problem. The water will come out of the vent, which is under a cover on the top of the downstream side of the valve (you can see the vent holes under the cover if you turn the valve upside down and look for them.) If water does come out of the anti-siphon it means something is wrong that needs to be fixed. In most cases it means either a stick or rock got into the anti-siphon seal and jammed it open, or the anti-siphon valve was not installed higher than all the sprinkler heads or emitters.
Never install a anti-siphon valve upstream of any other valve. If you do the anti-siphon valve will not prevent backflow and you have wasted your money buying it. (Exception: drain valves.)
Never use an anti-siphon valve as a backflow preventer installed on the mainline upstream of other valves. This is a common error that a lot of people make. I have heard employees at home improvement stores recommend installing a anti-siphon valve as a backflow preventer with standard electric globe valves installed after it for each of the sprinkler zones. I have seen many contractors do this also. Both should know better! Don’t you do it!!! It will damage the anti-siphon valve. Plus the anti-siphon valve will not prevent backflow when installed this way. You are no better off than if you didn’t use a backflow preventer at all. (Contractors and suppliers: before you flame me for being wrong, do some research. Don’t embarrass yourself! Most anti-siphon valves have a warning on the box or in the installation instructions about this. Just read the instructions!)
If you plan to use anti-siphon valves, every one of your sprinkler or drip zone control valves must also be an anti-siphon valve. You can use a ball valve upstream of the anti-siphon valves for an emergency shutoff. But no valves may be downstream of them. If you are paying attention you will note that essentially this is the same thing I said in #1 and #2 above! So hopefully you’re getting the message by now!
Anti-siphon valves should never be installed below ground.
You can build an enclosure around the anti-siphon valves to hide them. But they must be above ground, and the enclosure must allow water to freely drain out of it if the anti-siphon valves leak.
Pressure Vacuum Breaker. A pressure vacuum breaker (PVB) is similar to a atmospheric vacuum breaker except that you only need to install one of them and it is installed on the mainline leading to the control valves. Like the AVB it must also be installed above ground and it must be 6 inches (150mm) higher than the highest sprinkler head or drip emitter controlled by any of the valves. In a sloped yard it would typically need to be installed at the highest point in the yard, with a mainline pipe running up to it from the water source, and then another mainline running back down to the control valves.
A few local authorities require that the PVB be installed within 18 inches (450mm)of the connection to the water source, in which case you can’t use a PVB unless the water source is at the high end of the irrigated area. It may not be installed in any location where it might ever be submerged under water. Some municipalities do not allow the use of PVBs with drip irrigation systems. Some don’t allow the use of a PVB at all, so check with your water provider. A PVB backflow preventer may spit or spill water out from under the cap when backflow occurs, so it should be installed in a location where water spillage would not cause problems.
Warning: If used on a water system where a pump and pressure tank supplies the water (like is used on most rural homes that have a well), the PVB may spit water each time the pump shuts off. This is because the pressure variations caused by the pump and pressure tank system can cause backflow from the irrigation system back into the water system. The likelihood of water spitting, and the amount of water that spits out, both increase with a longer mainline on the irrigation system. So if you have 10 feet (3m)of mainline between the PVB and the farthest valve there is less likely to be water spitting than if you have 500 feet (150m) of mainline pipe. One way to stop, or at least reduce, this water spillage is to install a spring-loaded check valve right after the PVB. The PVB may still spill a little water with the check valve installed, however in most cases it should be much less water.
Reduced Pressure Backflow Preventer. The reduced pressure backflow preventer (R.P. Unit) is the king of the backflow preventers, made for high-hazard uses. It is also an expensive piece of equipment. It is the standard for commercial irrigation installations. This is the type of backflow preventer that I use on most of my designs. The R.P. Unit must be installed 12 inches (300mm) above ground, but it does not have to be higher than any of the sprinklers. It may not be installed in any location where it might ever be submerged under water. If installed in a structure or basement there must be a drain located near the backflow preventer. A single R.P. Unit is installed upstream of all the valves. R.P. Units are used for many things other than irrigation systems. Drive through any commercial business area and you will likely spot a lot of these units, most often sitting right out by the street. Many times you may see several grouped together, each used for a different purpose. R.P. Units may spit out water if they detect backflow, they also spit water if they are broken. So don’t install them inside a building without providing a floor drain.
Double Check Backflow Preventers. Depending on who you ask, double check backflow preventers may or may not be appropriate for irrigation systems. In many communities they are legal to use, and even recommended by local officials. Other communities do not allow them to be used on irrigation systems. I will attempt to present both sides of the argument.
Don’t be fooled! A “Dual Check” is NOT the same thing as a “Double Check Backflow Preventer”! They sound very similar, and they are “relatives”, but they are not the same. Dual check backflow preventers are for use with non-toxic materials. A typical use for a dual check is to install it where your house water supply connects to the water district’s pipe. The water in your house is (hopefully!) non-toxic, so a dual check is OK. The water in your irrigation system is not as likely to be non-toxic, so a dual check is NOT OK! So how do you recognize which is which when you see them? A Double Check will ALWAYS have two manual valves, one on the inlet and one on the outlet. These manual valves are used as emergency shut-offs and are also necessary to properly test the operation of the backflow preventer. A Double Check will also have test cocks (small outlets sticking out of the side of the backflow preventer) for connecting to test gauges. If it doesn’t have those shut off valves and test cocks it is NOT a Double Check Backflow Preventer! Many communities that allow double check backflow preventers do not allow the use of dual check backflow preventers. Don’t mistakenly buy the wrong thing! For more on dual checks, click here.
First let’s take a look at what a double check is and how it works. A double check backflow preventer is simply two spring-loaded check valves in a row, with a shut-off valve on either end and test cocks to allow the unit to be tested for proper operation. The double check backflow preventer is the only true backflow preventer which does not have a vent to allow air to enter the lines or to allow water to escape when backflow occurs. It relies entirely on the tight seal of the two check valves to prevent backflow. In most places where double check backflow preventers are legal, local officials will allow them to be installed underground in a vault. But not all do, so you should always check with local officials before installing the unit underground. Double check backflow preventers can be installed lower than the irrigation system and often they are installed in basements in order to protect them from freezing. Regardless of where they are installed they must be readily accessible for maintenance and testing. Even in areas where double check backflow preventers are approved for use they may not be used on any irrigation system where chemicals (fertilizers, pesticides, fungicides, pipe cleaning agents) are injected into the irrigation water.
Dual Check Device. Technically this one is NOT a backflow preventer. It is essentially a stripped down version of the Double Check Backflow Preventer, without the shut-off valves or test cocks. So what are they made for? Just to confuse people? It may seem like it! What they are is a flow control device rather than a backflow preventer. Now I admit there is a thin line of difference between the two. A typical use for a dual check is to install one after a water meter to prevent the meter from running backwards (gee, I wonder why the water company wouldn’t want that to happen?). OK, to set the record straight, I have heard that some authorities do suggest the use these devices as backflow preventers. In most cases they are requiring them in locations where the general consensus is that no backflow preventer is needed at all. (Most municipalities do not require backflow preventers on water supplies to single family homes, provided water is only used for drinking. The authorities assume that your toilets, washing machines, bathtubs, and dishwashers all have built-in backflow preventers– which pretty much all of them do.) But some authorities apparently are allowing, and even recommending(!!!), that dual checks be used for irrigation systems, and this is very risky. What if someone wanted to build a nuclear power plant a few blocks from your home, and they decided to build the cheapest model available, one that wasn’t even designed to be used as a power plant? Then to save even more money, they decide to leave out all the test equipment used to confirm that it is not overheating or leaking radiation? Only Homer Simpson could get excited about that! So why would anyone in their right mind use a flow control device that has been stripped of all it’s test equipment as a backflow preventer?
Pressure Losses in Backflow Preventers
To find the pressure loss through the backflow preventer you will need to consult the manufacturer’s literature. All of the following backflow preventer types are available in several sizes.
Atmospheric vacuum breaker. Although you may have several atmospheric vacuum breakers on your system, the water will only flow through one of them on its way to the sprinklers or emitters. So you only include the pressure loss for one vacuum breaker in your calculation. Most manufacturers don’t have pressure loss information for vacuum breakers, so assume a pressure loss of 2 PSI for a vacuum breaker if no manufacturer’s literature is available.
Anti-Siphon Valves. If you plan to use an anti-siphon valve enter 0 as the backflow preventer pressure loss. The backflow preventer is part of the anti-siphon valve and the pressure loss is included with the valve so you will enter it later.
Pressure Vacuum Breaker. You will need to obtain the manufacturer’s pressure loss information for the pressure vacuum breaker you plan to use. As a general rule pressure losses for pressure vacuum breakers range between 2 and 5 PSI, so using 5 PSI would be a fairly safe figure.
Reduced Pressure Backflow Preventer. You will need to obtain the manufacturer’s pressure loss information for the reduced pressure backflow preventer you plan to use. As a general rule pressure losses for reduced pressure backflow preventers range from 8 and 12 PSI. So using 12 PSI would be a fairly safe figure. Pressure losses for reduced pressure backflow preventers are very high compared to other backflow preventers due to the method they use to prevent backflow. The pressure drop is used to detect the backflow and redirect the water out of the bottom of the backflow preventer. Yes, it will spit water from time to time so make sure you provide somewhere for the water to go!
Double Check Backflow Preventer. You will need to obtain the manufacturer’s pressure loss information for the double check backflow preventer you plan to use. As a general rule pressure losses for double check backflow preventers range from 3 and 5 PSI. So using 5 PSI would be a fairly safe figure.
Check Valves and Dual Checks. There are two other types of backflow preventers available that you may run into. The first is a check valve. The second is a “dual check”. It is NOT the same thing as a Double Check even though it may be marketed as one! Don’t get ripped off! Pressure losses through a check valve tends to be about 3 PSI, Dual Checks have losses similar to Double Checks (5 PSI).
All backflow preventers must be installed correctly. Follow the instructions that come with the units. Backflow preventers should be checked yearly for proper operation. In areas where it freezes, the backflow preventer should be protected from freezing. See the Irrigation System Winterization tutorial for details.
This page is linked into several of the tutorials. If you are working through one of the tutorials, please select below to continue the tutorial you are using, or use your browser’s back button.
Definition of irrigation mainline: The mainline is all the pipes between the water source (POC) and the irrigation zone control valves. Another definition is that mainline is any pipe that is always pressurized with water.
Worksheet for Choosing Your Mainline Pipe or Tube
Excessive Water Pressure: In all cases if your static water pressure exceeds 100 PSI it is advisable to install a pressure regulating valve at the irrigation connection point to maintain a pressure lower than 100 PSI. All of these pipes or tubes may burst at higher pressures.
Temperate Areas (ground doesn’t freeze in winter)
Rocky Soil: Is your ground very rocky, so that it would be impossible to keep rocks larger than 2″ diameter from contacting the pipe? If “yes” consider using PEX tubing for you mainline.
Normal soil: If ground is not rocky consider using SCH 40 PVC pipe for your mainline. If pipe larger than 2″ is needed use Cl 315 PVC pipe.
Frost Areas (ground freezes at least a couple inches deep in winter.)
If your static water pressure is less than 60 PSI the use of 125 PSI rated poly tube may be sufficient if cost is a major issue. However it would be better to use 160 PSI tube if you can afford it.
For static water pressure between 60 and 80 PSI, use 160 PSI rated poly tube.
For static water pressure between 80 and 100 PSI, use 200 PSI rated poly tube.
Make sure you provide a method to blow out or drain the water from the mainline completely during winter.
Pipe or Tube Size: There is no easy way to say what exact size you should use. It you really don’t want to do calculations the following is a very rough educated guess that will work for most (but not all) situations. Use a pipe or tube size that is the next size larger than the water supply pipe the irrigation system (POC) is tapped into. Do not use smaller than 3/4″. Ie; if the irrigation system mainline is going to tap into a 1″ house water supply pipe (POC), then use a 1 1/4″ size mainline for the irrigation.
Pipe Depth: Bury the mainline pipe at least 18″ deep from the top of the pipe to the ground surface. It is critical that this pipe be protected from accidental damage and light frosts.
No water running through the house! To avoid nasty surprises, avoid using a water supply (POC) for your irrigation system that passes through a house inside the walls, under floors, or through the attic.
Keep reading for in-depth details and answers to “why?”
This page explains everything you need to know about irrigation valves!
There are many different kinds of irrigation valves available. You will need at least two different types for your irrigation system.
1. Emergency shut-off valve:
This valve should be installed at the closest point possible to your water source, that is, the location where you tap in for the irrigation system. Without this valve you will need to shut-off the water to the entire house when you want to work on the mainline or irrigation valves. The most commonly used valves for this purpose are “gate valves” because they are inexpensive. Unfortunately the cheap gate valves you’re likely to find in your local hardware store also tend to fail after a very short period of time. I recommend that you use a “ball valve”, or if you need a really big shut off valve (over 3 inch size) use a “disk valve”, or “butterfly valve”. These cost a bit more but are much more reliable and will last several times longer. So if you pay twice as much for a ball valve it’s probably still the best deal! If you want to use a gate valve make sure that it is a “wedge” type and buy a good quality one (it will probably cost more than a ball valve.) There’s nothing worse than trying to repair a system when you can’t shut off the water completely. OK, that’s about all you need to know about emergency shut-off valves. The rest of this page is about Irrigation Control Valves.
2. Irrigation Control Valves:
These are the valves that turn on and off the sprinklers, they also may be used for drip irrigation systems. Other names sometime used for them are irrigation valve, sprinkler valve, solenoid valve, and lawn valve. Sometimes they are incorrectly called Garden Valves. A garden valve is a manual valve that you connect a garden hose to.
Globe Valves vs. Anti-Siphon Valves
You have two basic styles of control valves to choose from.
Globe or angle valve:
This valve is available in any size and is commonly installed underground in a box or vault. Since it doesn’t incorporate a backflow preventer you must provide one separately. See the article on backflow preventers. The globe style valve is the most commonly used valve on commercial and larger size sprinkler systems.
Available only in 3/4″ and 1″ size. This is the most common used valve style for homeowners. The anti-siphon valve incorporates a backflow preventer into the valve. This saves a considerable amount of money, as backflow preventers are very expensive. The anti-siphon valve MUST be installed above ground and MUST be at least 6″ higher than the highest sprinkler head. This means that if you want to use anti-siphon valves you will have to locate the valves at the highest point in your yard, and run a water supply pipe to them from the water source (this water supply is called a “mainline”). The mainline pipe leading to the anti-siphon valves should be buried 18″ deep to protect it.
Valve Operation/Control Systems
Manual, Hydraulic and Solenoid Valves:
The sprinkler valves may be manually operated or they can be remotely controlled (automatic valves.) Manual control is simple, the valve has a handle that you use to turn it on and off using your hand as the power source. Remote control valves are either electric or hydraulic operated using a timer or other signaling device to tell them to open and close. Today almost all of sprinkler control valves are electric powered solenoid valves. The electric solenoid valve operates on 24 volt alternating current (vac) and is turned on and off by a timer called an “irrigation controller” or often just “controller”. Anti-siphon, globe, and angle valves styles are all available as automatic valves.
Solenoid Valve and Controller Compatibility
Pretty much all 24volt valves and controllers are compatible with each other. The most common exception to this rule is valves operated by controllers that are battery or solar powered. (By battery powered I mean they are not plugged into a power source other than the battery. Many controllers have a battery to prevent program loss in case of a power failure, these are not “battery operated”.) So in most cases you can buy a brand “X” controller and it will work fine with brand “Y” valves. You can even mix two or more brands of valves together if for some reason that appealed to you. For example the irrigation system where I test valves and controllers has many different brands all running together. If the valve is not “universal” or compatible it will typically have a warning on the packaging.
I strongly recommend that if you are going to use automatic valves, you select a valve model that has a manual flow adjustment control feature on it. Don’t confuse the flow control with a manual on/off switch. The flow control is a separate handle (sometimes a screw) in addition to the manual on/off control on the valve. This flow control feature is not found on many of the less expensive “budget” valves. The flow control bypasses the automatic valve features allowing the valve to be closed in an emergency by turning a handle just like a standard manual valve. More important is that it also allows the valve to be “throttled”, that is, the water flow may be adjusted to any rate desired. This ability to adjust the flow rate is very useful in many different situations, both when installing your sprinkler system and later when managing it. It can literally make the difference between being able to make a troublesome valve work and having to remove and replace it! I very strongly suggest that this is a feature worth the extra cost.
Using the manual flow control you can manually force the valve closed if it sticks open. The manual on/off switch will not close the valve if it is stuck open. Failure to close automatically is one of the most common valve problems, so there’s a good chance that someday you will use the flow control to force closed a valve that is stuck open.
If your flows are on the low end of the valve’s operation range, it may be helpful to throttle down the flow control to make the valve close faster and more reliably. Without the flow control feature you may have a lot of problems in this situation, you will probably have to replace the valve.
Partially closing the flow control will make the valve close faster, which is not something you want to do normally, but sometimes it is desirable. On automatic systems it is common for the next valve to open before the previous one fully closes. The resulting loss of pressure due to two valve circuits being on at the same time can cause the first valve to never fully close. A flow control on the valve can help correct this problem.
Buy valves with the flow control feature. Just do it. Don’t be one of the many people who later makes some lame excuse to me, like “the guy at the store, who normally works in the paint department but was filling in for the day on the irrigation aisle, said it was a waste of money!”
Should You Use Metal or Plastic Valves?
Sprinkler valves come in both brass and plastic models. Most valves used today are plastic, but brass is not out of the picture. There is no doubt that a brass valve will last longer in most situations, especially if installed above ground in the sunlight. From an operational point of view both are reliable, especially for automatic systems. For manual valves my experience is that plastic valves wear out fast and have a very short life. Brass will last much longer. If you use plastic valves above ground you may wish to consider building a cover for them to protect them from sunlight, which can destroy the plastic over time.
Two types of plastic material are used for valves. Glass-reinforced nylon is the best, it is tougher, more resistant to impact, and has a higher pressure rating. PVC is used for lower cost valves, it still is pretty strong, although that really depends on how thick the plastic is! A few valves use ABS plastic or polyethylene, especially for minor parts like screws or caps. Both of these plastics are less strong and are typically used for parts with little stress on them. I recommend avoiding valves with “solvent weld” connections (the pipe glues directly into the valve.) If the valve fails, they can be difficult to replace. Only the cheapest valves come with solvent weld connections. Hmmm… cheap valves fail more and with glued ends are harder to replace- sounds like a bad idea.
Jar Top or Traditional Top Held on with Screws?
OK, just personal opinion here, but I don’t see any advantage to a jar top valve. Yes, they seem to work as well as a top with screws holding it on. They primarily are only found on cheaper valves. The only selling point I have heard for them is that they are supposed to be faster to open for repairs. Are you repairing it that often? I hope not! But I guess if it is a cheap valve…? My experience is that by the time the valve is old enough to need repairs the jar top has seized up and it takes a strap wrench to get the top off. Personally I prefer using a simple screwdriver to remove a few screws as opposed to wrestling with a strap wrench in a tight spot like a valve box.
Today’s valves are pretty maintenance free. Almost all automatic valve failures result from installation or design problems. Ignore the following and you will hate your valves regardless of what type or brand you buy!
Join the “Hall of Regrets”! Simply ignore the following advice, then send me your “I’m an idiot, I wish I’d listened…” sob story. I’ll add it to my collection and shed an alligator tear or two for you!
Dirt in the irrigation pipes. Inside the valve there are very small water passages that lead to and from the solenoid. Water must flow freely through these small passages. If a grain of sand or glob of algae gets into these passages it can block them and the valve will fail to open or (more likely) fail to close. It is critical to flush all the dirt out of the pipes before installing the valves. A 100 to 200 mesh filter installed at the water source connection can also help keep out contaminates that comes in with the water supply. You may be surprised to learn that most water companies have considerable amounts of sand in their pipes. When you install a new sprinkler system the higher flows stir up this sand and then it gets into your new system. That’s why I suggest to you in the installation tutorial to flush for so long. You have to get the sand out of both the sprinkler system pipes and the water supply pipes! I can’t stress this enough! It’s like a cheap low-flow toilet. You have to flush, flush, and flush again!
Almost all valve solenoid failures are caused by water getting into the solenoid. The water gets into them through the wires. The solenoid wires have multiple strands of wires twisted together with insulation around them. Because they are twisted there are very small gaps between the wires which form passages along the length of the wire. Water is sucked up through these small passages and deposited into the solenoid by capillary action. Thus it is critically important that the wire splices on the valves be completely water proof so that water can’t be sucked into the solenoid through the wires. You should water-proof the wire splices right after you test the valves! No kidding, a single drop of water on the bare valve wire end can be quickly sucked up into the solenoid and will ruin the solenoid. The Installation Tutorial has more on this.
Valve Size and Pressure Losses:
Emergency Shut-Off Valve:
The pressure loss through the emergency shut-off valve is not significant enough to worry with. We will ignore it. The emergency shut-off valve should be the same size as the pipe it is installed on. If a smaller size shut-off valve is used then you do need to worry about losing pressure through the valve. Probably about 2 PSI would be a safe assumption of the pressure loss.
WARNING!!! If you use the wrong size automatic valve, the valve may not work! READ THAT AGAIN! Let it sink in. The correct valve size often will not be the same size as the pipe it is connected to.
The pressure loss in an automatic solenoid valve is the primary energy source used by the valve to open and close the valve. The electricity sent to the valve solenoid is just used to jump-start the process, the real force used is the water pressure. If the valve doesn’t have enough pressure loss it will not have the energy needed to close by itself. Always size automatic valves based on the flow rate using the manufacturer’s chart as a guide. Never assume that the valve should be the same size as the pipe! It is very common for the valve to be a different size than the pipe it is installed on. I have seen some rare cases where a 3/4″ valve was the proper size for the flow through a 2″ pipe!!! If you absolutely must guess, use the next solenoid valve size smaller than the pipe size and assume a pressure loss of 6 PSI. Never guess if your flow is less than 5 GPM, always use a chart! Many automatic valves won’t work at all at flows below 5 GPM!
The size of the automatic valves is determined by the manufacturer’s recommended flow range, together with the pressure loss through the valve at the selected flow. You will need to get the valve manufacturer’s flow chart for the model of valve you plan to use. This information should be on the valve packaging. If you can’t find it on the package, try the valve manufacturer’s website or ask for a data sheet on the valve at the store where you buy the valve. (At discount home improvement stores you are likely to get a blank stare from the employee if you ask for a data sheet!)
Some valves don’t appear to have data sheets available anywhere, so as a last resort I’ve assembled some data for you based on my own research for some of the more popular ones. You will find it in the reviews on this website, Click Here. That said, if the valve manufacturer doesn’t provide this necessary information it shows an extreme lack of professionalism, I would be very reluctant to use the product!
If you can’t find pressure loss and flow range information for the valve you want to use, I strongly suggest you use a different brand of valve. After the valve is installed is not a good time to discover it’s the wrong size and won’t open or close automatically!
Example: let’s say you are going to use an automatic anti-siphon type valve. Your Design Flow is 20 GPM, so for now we will assume the flow through the valve will also be 20 GPM. (If it turns out the flow will be less,you can resize the valve later.) The manufacturer’s flow chart would look something like this:
Doesn’t Work Valve Company, Inc. – Valve Performance Data
3/4″ Anti-Siphon Valve
1″ Anti-Siphon Valve
Warning: The chart above is not real. DO NOT USE THESE VALUES!
The example chart above tells us that the pressure loss for our valve at 20 GPM flow would be 8.0 PSI if we used a 3/4″ valve and 4.0 if we used a 1″ valve. So we could use either one. The pressure loss information from the chart would be the number that you write into your Pressure Loss Table on the “_____ PSI – Valves” line. So if we decided to use the 3/4″ valve, the value would be 8 PSI. But what if after adding all the pressure losses in the loss table, you discover that the losses are too high? In that case you could go back and change to a 1″ valve. That would reduce the pressure loss down to 4 PSI, rather than 8. With that said, as a general rule I try to avoid losing more than 6 PSI through a valve. So I would not use a 3/4″ valve in the example above if it were my sprinkler system. Why? Valves need pressure drop for them to work correctly, but really high pressure losses are hard on the valve. As the pressure loss through an automatic valve increases, the speed that the valve closes also increases. Thus a high pressure loss can cause the valve to snap closed extremely fast, and that is bad for the entire sprinkler system. Plus the water is moving extremely fast through the valves at those higher pressure loss rates, resulting in more wear on the valve seats. So the valve will fail earlier.
If you looked closely at the chart above you may have noted a couple of interesting items. First, and most obvious, is that no pressure loss is given for a 3/4″ valve at 25 GPM. This is because that flow is outside the acceptable range for the valve. You should not use the valve for that flow. The next item is less obvious, but if you look closely, you will notice the pressure loss for the 1″ size valve is less at the 15 GPM than it is at the lower 10 GPM flow! No, it isn’t a mistake. It is very common for valves to have higher pressure losses at very low flows, so if you notice this on a flow chart; don’t panic, it’s not a misprint.
Can a valve be smaller than the pipe it is connected to?
As you move through the tutorial you will find that even though the valve will handle a certain flow, that flow is often too high for the same size of pipe. So it is very common to have a valve that is one, or even two, sizes smaller than the pipe it is installed in. In fact it is so common that they actually make special pipe fittings (connectors) for this. For example they make a PVC plastic male adapter that glues onto 1″ pvc pipe, but has 3/4″ threads to allow you to install a 3/4″ valve on a 1″ PVC pipe. They also make one that glues onto 1 1/4″ pipe but has 1″ threads.
For Manual Valves:
Manual valves are much more forgiving than automatic valves. You don’t need to worry about having enough pressure to allow the valve to close by itself, it uses “elbow grease” to power it! However, you still need to find out what the pressure loss through the valve will be so you can enter it in your Pressure Loss Table. As with the automatic valves, you use a chart provided by the manufacturer for this. Follow the same procedure given above for automatic valves. Unfortunately, pressure loss data for manual valves can be hard to find as many manufacturers don’t provide it. As a general rule, allow 2 PSI pressure loss for a globe or angle type manual control valve, 5 PSI if it is an anti-siphon valve. Manual irrigation control valves should be of the “angle” or “globe” type with replaceable rubber seats. Never use a gate valve as a control valve. Gate valves are not made to be regularly opened and shut. Many gate valves will start leaking after as little as 10 uses!
Want to use a manual valve now but change to an automatic valve later? No problem. Simply design for the automatic valve, but use the manual one instead. Then you can replace it later when you want to automate the system. Another way to do this is to install the automatic valve and simply operate it manually using the manual on/off lever. If you do this, then later you just install a controller as well as wires between the controller and the valves and you have an automatic control system.
Elevation changes can add or subtract water pressure from your water system. That seriously changes how well the system works. Each foot of elevation change is equal to 0.433 PSI of water pressure. Think of a vertical column of water. At the bottom of the column the weight of all the water above is resting on the bottom of the column, this weight creates pressure. Have you ever swam down to the bottom of a deep swimming pool and felt your ears pop or hurt? That’s caused by the increased water pressure pressing against your eardrum. The deeper you go, the more pressure you feel.
Not Just for Irrigation
While this page is written for irrigation design, these same principles apply to any piping system that carries water in it. The elevation impacts described here would apply to a huge city water system, to the pipe bringing water from a well to a rural home, or a pipe taking water from a creek or pond to a remote tank. If you jumped here from an Internet search and are not working through the irrigation design tutorial this page is part of, remember that when designing a water piping system you must consider other sources of pressure loss in your design too, such as friction loss caused by the water moving through the pipe.
In the USA we measure water pressure most often in pounds per square inch (PSI). That’s the weight in pounds of the water on a one-square-inch surface area. Sometimes we measure pressure in “Feet of Head”, especially when dealing with pumps and wells. This is to confuse you. (Not really.) We also don’t use metric here in the good old USA. We do this to annoy the rest of the world. (No, we really do it because we are lazy and unwilling to adopt the metric system.) So if you are outside the USA water pressure is measured in bars… or kiloPascals (kPa). Or about a half dozen other measurements. Unfortunately the rest of the world is no more agreed on how to measure water pressure than we are! There are simply a lot of systems used to measure pressure. Fortunately a conversion calculator will allow you to switch back and forth between any of them. If you don’t like that calculator or it isn’t working there are many more, just search for “pressure conversion calculator.”
My tutorials mostly use PSI, although I use Feet Head in parts of the pump related tutorials and metric for drip systems. OK, now it’s class time!
You can skip down past this section if you wish. Look for the next horizontal line. This section is for those who need to know “why?” or want to understand hydraulics.
Since water is essentially a non-compressible liquid it exhibits the unique trait of transferring pressure horizontally when in a confined space. What this means is that water in a pipe (which is a confined space) exhibits the same pressure as it would if the pipe were perfectly vertical, even if the pipe isn’t. This isn’t an easy principle to understand, so be patient and re-read as needed. The best way to demonstrate this is with a picture.
In this picture the water pressure in the water tank at the top of the water surface level is 0 feet of head, or you could also say there is 0 PSI. This is because there is no water above it to create pressure. Head is another word that indicates pressure, it is mostly used when measuring pressure created by the depth of water. So 10 feet deep water will create 10 feet of head at the 10′ deep level. So 10 feet of depth = 10 feet of head. Ok? (Yes, I know there would be a small amount of additional water pressure due to the air pressure above the water, but let’s try not to confuse things. This is hard enough to understand! So we’re going to say that there is 0 feet of head at the water surface.)
Looking again at the picture above, we see that the ground level is 40 feet below the water level in the tank. Therefore the water pressure at ground level is 40 feet of head. Again 40 feet of depth = 40 feet of head. Now lets convert that to pressure measured in PSI. As noted earlier, 1 foot of elevation change creates 0.433 PSI of water pressure. So in this case 40 feet of head is going to be about 17 PSI. (40 ft head x 0.433 psi/ft = 17.3 PSI.) Again, the formula is “feet of head x 0.433 = PSI.” So far, pretty straight forward. Read again if you’re confused.
Static Water Pressure
Now the hard to understand part. In the drawing above, the water enters the house at a level 100 feet below the water level in the tank. So the static water pressure at the house is 100 feet of head, or about 43.3 PSI, using the formulas in the previous paragraph. Note that I said this is the “static pressure”. So now you’re likely wondering how this could be? The water level is not just 100 feet above the house there is also easily 180 feet of pipe between the tank and the house! The answer is that the length of a pipe does not matter when the water is static in the pipes. Static means the water is not flowing, it is not moving, it is standing still. This is very important! Because the water is a non-compressible liquid it transfers the pressure horizontally along the pipe route for pretty much any distance without any loss of pressure! Cool, right? You bet it is, it is a principle that is very handy and makes all sorts of neat gadgets used on machines work. This is why a small hose filled with hydraulic fluid can cause the brakes on every wheel of a mile long train to apply when the engineer hits the brakes!
Now on the other hand, if we measured the pressure with the water flowing, then the pressure would be termed “dynamic pressure”. With the water in a dynamic state (flowing in the pipe) the water would loose pressure due to friction on the sides of the pipe and we would get a lower pressure reading at the house shown in our previous diagram. (I’ll deal with dynamic pressure in the next paragraph.) So for now, just understand that static pressure means there is no flow in the system, so there is no friction, and no pressure loss! Read that last sentence again! Think about it for a second, go back look at the picture again if you need to. It makes sense if you think about it. Our professor spent a week drilling this concept into us back in college and a lot of people in the class never did understand it! So if you still don’t get it don’t feel bad and don’t get discouraged! Just accept it on faith (I wouldn’t lie to you) and continue on.
In most cases we use static water pressure values when designing irrigation systems (or any other water piping system for that matter.) Then we can use calculators, spreadsheets, or charts (if you really want to torture yourself you can even use a very complicated manual calculation) to estimate the “friction loss” that will occur in the pipes when the sprinkler system is operating. Then we will subtract the friction loss from the static pressure to arrive at the dynamic pressure. Why not just turn the water on and measure the dynamic pressure with the water flowing? It would seem simpler, then we would not have to prepare a separate calculation for friction loss, right? Well, that is correct, however dynamic pressure is extremely difficult to measure accurately! You have to get the flow just right, and then hold the flow at that level for a minute or two while the pressure stabilizes. This is a real pain in the rear to do and not nearly as easy as it sounds! Plus, it is a bit hard to do if the pipe isn’t installed yet! You can’t measure the dynamic pressure if the pipe isn’t installed! So, the result is that we almost always will work by using static water pressure and then use calculations to determine the dynamic pressure. Its just way easier to do, and who wants to do it the hard way?
Now go back and look at that picture at the top of this page of the tank and house again. As the water flows to the house the water level in the tank will go down (assuming water isn’t flowing into the tank to refill it.) So the elevation of the top of the water in the tank will drop as the tank empties. When the tank is almost empty the difference might be only 95 feet. So since the water depth is less, the water pressure would also be lower. This happens all the time and is normal! If the top of the water elevation varies, then the water pressure will also vary. So if the water level will vary at your water source, the pressure will also vary. I know I keep saying the same things over and over in different ways, but I’m trying to drive home some important, but hard to understand, principles! My apologies if you got it the first time through and are getting bored!
Still confused? Don’t worry about it, just follow through the procedures that follow and you’ll be all right even if you don’t fully understand why you’re doing some of these things! Just remember that whenever you measure water pressure with a gauge you need to turn off all the water outlets so the water is static, that is, not flowing.
Time to wake up!
Hills, Valleys, & Slopes Continued…
In a nutshell: Just remember every foot of elevation change causes a 0.433 PSI change in water pressure. If your pipe is going downhill add 0.433 PSI of pressure per vertical foot the pipe goes down. If the pipe is going uphill subtract 0.433 PSI for every vertical foot the pipe goes up. The word “vertical” is critical. If the pipe goes up a slope the vertical distance is how high the slope would be if the pipe were going straight up. Do not use the length of the pipe, use the change in elevation! If you don’t want to accept my word for it then you’re going to have to go back and read all that boring Hydraulics 101 stuff above!
Because elevation changes effect the water pressure we must take this into account when determining pressure loss in our water system. If the area to be irrigated is lower than the water source we will gain pressure, so we may be able to gain some beneficial added pressure to our system. Care must be taken though. We can only add pressure if ALL the irrigation system is lower. If portions of it are not lower, or are higher than the water source, then those portions aren’t going to be getting that extra pressure. It is safest when doing initial design work to just not add pressure for elevation changes unless you’re really sure.
On the other hand if portions of the irrigation system are higher than the water source you will always need to subtract out the pressure loss created by the elevation gain. Pressure gained can be easily disposed of, pressure lost however, is very difficult to replace. So, for every foot of elevation gain (higher) in the irrigation system, you should subtract 0.433 PSI from the design pressure.
The far corner of the irrigation system is 9 feet higher than the water source.
9 feet X 0.433 PSI = 4 PSI loss (loss because it is higher). The water pressure in the far corner will be 4 PSI lower than the pressure at the water source, simply because it is 9 feet higher.
One corner of the irrigation system is 20 feet lower than the water source. Another corner is 12 feet higher than the water source. 12 feet X 0.433 PSI = 5 PSI loss at the higher corner. However in the 20 feet lower corner the pressure will be higher. 20 feet x 0.433 PSI = 8 .7 PSI higher in the lowest corner. In some cases we might need to install a device to lower the pressure at the sprinklers in that low corner. But we’ll worry about that later. For now the high corner with the 5 PSI loss is more important. Remember, it is easy to lower the pressure if we need to, but it is hard to raise it.
A final example:
The water source is on a hill. The highest part of the irrigation system is 50 feet lower than the water source. The lowest part of the irrigation system is 60 feet lower than the water source. In this case you can add pressure because the ENTIRE irrigation system is lower. But the pressure added can only be the difference between the water source and the highest part of the irrigation system. 50 feet x 0.433 PSI = 22 PSI pressure GAIN. So you would subtract this amount from the total system pressure required. In other words you would enter a negative number in your Pressure Loss Table for Elevation Pressure Loss.
Too Much of a Good Thing:
What if one corner of the irrigation system is a lot lower than the other? While unusual, it is possible to have too much pressure! With too much pressure the sprinkler heads might not work as well, or they might even blow apart! For spray type sprinklers 40 PSI at the sprinkler head is the most pressure you want. For rotors it varies, but most small systems shouldn’t have more than 70 PSI at the rotor sprinkler head. If you have too much pressure you will need to reduce the pressure. Most sprinkler heads can be bought with a built in pressure reducing device. You can also buy an individual pressure reducing device that can be installed on the sprinkler head inlet pipe. These devices will reduce the water pressure to the optimum level for the sprinkler. Remember, the devices only reduce pressure, they can’t increase it! They will always reduce the pressure by at least a small amount, so they should not be used unless you have too much pressure. More on this topic will be covered when we get to discussing sprinkler heads so don’t worry about it now.
If you are working on a Sprinkler Design enter the pressure loss or gain caused by elevation changes on the “Elevation Change” line of the Pressure Loss Table. Enter the value in PSI. Remember, feet of elevation change x .433 = PSI.
This article is intended to give you an introduction to the various sprinkler heads used for irrigation. It will help you choose the best sprinkler for your situation. At the same time it will warn you away from some common and costly errors often made in sprinkler head selection. Similar information on bubblers is found in the last section of this page.
Types of Sprinklers:
Traditionally sprinkler heads are grouped into two broad types based on the method they use to distribute the water, spray type sprinklers and rotor type sprinklers. However new technologies are blurring the traditional boundaries between the types.
More properly called “fixed spray heads” these are the small heads that spray a fan-shaped pattern of water. Think of a shower nozzle. Most use interchangeable nozzles installed on the sprinkler which determine the pattern (1/2 circle, full circle, etc.) and the radius of the water throw. Some specialty patterns are available for long, narrow areas. Spray heads are spaced up to 18 feet apart. The basic physics of water spray limit the distance between heads. They need between 20 and 30 PSI of water pressure to operate properly.
Rotor is the term used to describe the various sprinklers which operate by rotating streams of water back and forth or in circles over the landscape. The example which most people are familiar with is the “impact” rotor sprinkler (often improperly called a “rainbird*”) which moves back and forth firing bursts of water. You probably know this sprinkler best for the distinct sound it makes when operating– tooka, tooka, tooka, tic, tic, tic, tic, tic, tooka, tooka, tooka, etc… The impact rotors are rapidly being replaced now by gear driven rotors which are very quiet, lower maintenance, and much smaller in size. It won’t be long before the average person has no clue what I am describing! These new turbine and gear driven rotors have one or more streams of water which move silently across the landscape. The prettiest of these are the “multi-stream rotors” where multiple streams of water rotate over the landscape one after the other. Multi-stream rotors are fascinating to watch. Rotors can be spaced from 8 feet to 65 feet apart. There are rotors available that can be spaced farther apart than 65 feet but I don’t advise using them in most situations, even golf courses are moving away from using them due to problems. The traditional rotors with spacings over 20 feet require a lot more water pressure to operate than spray heads. Here’s a rule of thumb, “The water pressure at the rotor head in (PSI) must exceed the distance (feet) between the heads.” (Known as Stryker’s Rule, admittedly that’s a little ego stroking on my part, but I did create the rule!) Thus if you want to space rotors 35 feet apart you will need 35 PSI of pressure at the sprinkler head. That means you will probably need around 45 PSI minimum to operate the system since pressure will be lost in the pipes and valves as the water flows to the sprinklers. More on that later. The small 3/4″ inlet rotors sold for residential use work best at 25 to 35 foot spacings.
(* Rain Bird is the name of a sprinkler company and is a registered trademark. The Rain Bird company makes many different types of sprinkler heads, including impact rotors. They also many other irrigation products.)
Rotary Nozzles & Rotators:
A new type of miniature rotor has been introduced in recent years and have become extremely popular. These are often called rotary nozzles or rotator nozzles. The first brand on the market was called the “MP Rotator”, and several other similar products quickly became available from other companies. Most manufacturers classify these as a “spray heads” in their catalogs. They are called rotary nozzles because they are a very small rotor that is the same size as the standard nozzle on a spray-type sprinkler. Thus they fit onto the smaller, and less expensive, spray head pop-up bodies. Rotary/rotator nozzles are more efficient than traditional spray heads because they produce less “mist” that evaporates before it reaches the ground. Thus they are often promoted for use in place of standard spray heads by water conservation agencies.
These rotary nozzles have a radius generally between 15 and 35 feet*. The exact distance depends on the model. They all use multiple streams of water that rotate around the nozzle and look like rotating spider legs.
*New models are being introduced each year as the technology advances and I expect to see shorter radius rotators available. Already there are add on devices like the Little Valve brand devices that will reduce the radius of a rotator.
A few words of caution on rotary/rotator water savings claims:
Keep in mind that the water savings are primarily found when comparing rotators to spray heads. For spacings over 20′ it is typical to use rotors rather than spray heads. I haven’t seen any independent lab data that suggests that using a rotator nozzle in place of a rotor head will save water. (As of 2013.)
Like all other claims you must compare apples with apples. I once had a city official, who obviously had just been visited by a rotary nozzle salesman, order me to replace all the sprinklers on a shopping center irrigation system with “rotators”. The planters I was watering were 6 feet wide, and at that time the smallest rotator on the market had a minimum radius of 15 feet. Thus if I had done as he suggested I would have been watering 9 feet of the parking lot! Not a good move if you want to save water… The moral of the story is that you need to use your head and select the right product for your situation. Replacing a 6′ radius spray head with a 12′ radius rotator is NOT going to save any water! Yet I hear that same blanket statement “switch to rotators and save water” over and over.
Guide to Selecting the Right Sprinkler Type:
Which to use, sprays, rotary nozzles, or rotors? Here are some questions to guide your selection.
Is your water pressure less than 40 PSI static? If so you should consider using sprays or rotary nozzles.
Is the area long and narrow, between 12-28′ wide? Then you should look into rotary nozzles. They may also be appropriate for narrower areas, at the time I am writing this Hunter has introduced a “side-strip” rotator for 4 to 5 foot wide strips that are at least 12′ long. More combinations of widths will likely be introduced in coming years.
Is the area you want to water greater than 30′ x 30′ in dimensions? If so, rotors may be the best solution.
Is the edge of the area to be watered curved? If the edge has sharp curves (less than 20′ radius) then rotors with longer radii will have difficulty watering the edges without over-spraying them. This may not be an issue depending on what is beyond the edge. If the area beyond the edge should not get water on it you might want to consider a smaller rotary nozzle or spray-type sprinkler.
Installation Issues related to Sprinkler Selection:
Rotors and rotary nozzles are spaced farther apart than sprays. Therefore installation of them requires less pipe and trenching, but they also cost more per sprinkler. For most normal-size city residential yards spray heads or rotary nozzles are usually the better choice.
Cost Issues in Selecting Type of Sprinkler:
Surprisingly regardless of the type of sprinkler you use, the cost per square foot of area irrigated comes out about the same, assuming correct design of course. When using rotors or rotary nozzles there is less pipe and trenches, but the rotors themselves cost more. Spray heads are less expensive to buy, but they require more pipe, trenches and valves to install. In the end, the price really comes out pretty close either way.
Note: If your static water pressure (“design pressure” on your Design Data Form) is less than 40 PSI rotors will not work properly, DO NOT USE THEM. See the previous pages of the Sprinkler System Design Tutorial if you don’t know what static water pressure or design pressure means. If you have a well and pump you must have your pump-on setting adjusted to no less than 40 PSI if you plan to use rotors. A “40-60” setting is typical. Contact your pump company for assistance.
If you are unsure, try using rotors in your design. If they don’t work out well, then erase them from your plan and try rotary nozzles. In many situations the best option maybe to use rotors in large areas, and spray heads or rotary nozzles in smaller or more narrow spaces. So you may have a mixture. This is OK, but there are some things you need to be careful of when mixing different types of sprinklers. The first is that each type must be separated and connected to a separate control valve. You can’t mix the types together on a single valve circuit or valve zone. More on this later in the tutorial. The second is determining how to space the heads where the different types meet each other. For example, if you have a 30′ radius rotor next to a 15′ radius spray head, how far apart should they be from each other? There are many different schools of thought on this, but my general recommendation is to split the difference. In this example put them 22′ apart. Yes, the rotor would overspray the spray head by a considerable distance. But if you put them 30′ apart you will get a distinct dry spot between them.
Basic Body Styles:
Pop-Up Style Sprinklers:
Pop-up style sprinklers are installed below ground. A piston that contains the nozzle lifts up from the sprinkler body when the sprinkler is operating and then retracts back below ground when not in use. Consider using pop-up style heads even in shrub areas. Pop-up sprinklers often don’t cost any more than shrub sprinklers when you include the cost of the riser (the upright pipe the sprinkler is mounted on). Two major advantages of pop-up sprinklers are safety and appearance.
What Pop-up Height Should You Use?
Pop-up style sprinklers are available in a variety of heights, generally 2″, 3″ , 4″ 6″ and 12″ are the common heights. Most of my commercial clients ask me to use at least a 6″ height, even for lawns. The extra height avoids problems. I wouldn’t use anything less than 4″ on fescue, rye, St. Augustine, or bluegrass lawns. For close mowed Bermuda grass 3″ will work. My experience is that the spray from 2″ pop-up heads are often blocked by even recently mowed grass! For that reason I do not recommend any model of 2″ pop-up, you will get dry spots in the lawn. For groundcover and shrubs use 6″ and 12″ heads.
Groundcover Design Trick:
Here’s a tip for watering a groundcover area next to a lawn. Place the sprinklers for the groundcover about 12″ away from the groundcover, in the lawn area, and aim them back at the groundcover. That way the groundcover does not block the spray as easily.
Shrub Style Sprinklers:
Shrub style sprinklers were a type of sprinkler head designed to be installed above ground on top of a pipe. In the old days they were used for shrub areas, thus the name. For liability reasons, most irrigation professionals no longer use shrub sprinklers, except in very limited situations where nothing else will work. You should take a hint from the pros and also avoid using them! Read the warning below! (For shrubs you really should look into using drip irrigation, it is a better choice than sprinklers for most situations.)
Many people are injured each year when they trip over, or fall on, shrub style sprinklers. Think Safety. Do not use shrub style sprinklers unless a very tall riser is needed to raise the sprinkler spray over the tops of tall shrubs. When needed, shrub style sprinklers should only be used in areas well away from sidewalks, patios, and areas where children play. They should be clearly visible. A good idea is to strap them to a large post, like a 4″x4″ wood or plastic fence post, to hold them stable and make them easy to see.
Metal or Plastic?
At the grocery store it’s “paper or plastic?” but with sprinklers the question becomes “metal or plastic?”. The conventional wisdom is that metal is more durable than plastic, and therefore is better. Up until the late 1970’s metal (usually brass, sometimes zinc) was the standard material from which almost all sprinklers were made. However, times have changed and now plastic is the most common material for sprinklers. Very few manufacturers even bother to make an all-metal sprinkler anymore. The primary reason for this change in materials is cost; machined metal parts are enormously expensive in comparison to injection molded plastic. Fortunately, most of today’s plastic sprinkler heads are very well engineered and will perform as well as, if not better than, the old metal sprinklers.
Hybrids: A few companies manufacture plastic sprinkler bodies which accept brass nozzles, which they claim results in a better water pattern. Other manufacturers claim that plastic nozzles perform as well as brass. The research tends to indicate that a really well-machined brass nozzle has better water distribution. But that’s laboratory tests, and in the real world a lot of other factors come into play. I personally haven’t noticed any significant difference in performance between most brass and plastic nozzles in well-designed, sprinkler systems, although brass nozzles will no doubt last longer. More importantly, there are a few nozzles, both brass and plastic, which don’t seem to perform as well as others. Fortunately, they are easily identified by comparing prices (as in “you get what you pay for.”) Typically these bad nozzles come pre-installed on sprinklers that don’t have the features I list below, so if you stick to sprinklers with my recommended features you will get acceptable quality nozzles.
Features to Look For:
The following features are common to all good-quality sprinkler heads (for both rotors and spray type heads.) Choosing a sprinkler without these features is asking for trouble.
Spring Retraction: Make sure a spring is used to pull the pop-up piston down into the case when the sprinkler isn’t on. As a general rule the stronger the spring, the less likely the piston will “stick up” and get mowed off. Stay away from sprinklers that rely only on gravity to retract the pop-up piston.
Wiper Seal: This is a soft plastic seal around the pop-up riser stem that seals the riser so it won’t leak . The wiper seal also is responsible for keeping dirt out of the sprinkler body, and is the most important part in determining how long the sprinkler will last. Make sure the sprinkler model you select has a wiper seal. Note: on some sprinklers you must remove the sprinkler’s cap and look inside the bottom of it to see the seal. Be careful when removing the cap, on some models the spring will shoot out!
3 Inch Pop-Up Height (or higher):Unless you just like to trim grass around sprinkler heads, make sure the pop-up height is 3″ or more. This way the spray nozzle will clear the top of the grass. Most professionals use 4″ pop-up sprinklers in lawn areas, and 6″ or 12″ pop-ups in shrub areas.
Rat Traps. This is a design type to avoid if you can. A “rat trap” is a derogatory name used in the sprinkler business to describe any sprinkler with a design that allows debris to fall into the sprinkler body when the riser is raised. The more proper name is a “bucket” style body, but I like the visual image of the problem that rat trap provides. The debris collects in the bucket area and eventually there is enough garbage in there to prevent the mechanism from dropping back down. The stuff that falls in there can get pretty ripe smelling as it decomposes, too! Do rats really get trapped in them? I’ve never seen one. The “trap” only opens when the sprinkler is operating and rats tend to stay away from a sprinkler that is operating! Mostly grass clippings and dirt get trapped.
Sprinkler Make and Model Recommendations:
Mix and Match. One common question I get from users of this tutorial is “who makes the best sprinkler heads” or “which model should I use?” This probably won’t help you much but most of my designs have a mixture of brands and models as I feel different products are best for different situations. But what you should get out of that is that it is OK to mix and match– within limits. On any single valve circuit you should use one brand and model of sprinklers only. This is because precipitation rates vary between makes and models and if you mix a high precipitation sprinkler on the same valve zone as a low one you will get mud in one area and dry spots in another. But you can create two different valve zones and use different sprinklers in each. So one valve might turn on a group of brand X rotors to water a large lawn area. Another valve might turn on a group of brand Y spray heads to water a small lawn in a parking strip. And a 3rd valve might turn on a drip system using brand Z emitters that waters some shrubs.
Brands and Models. While I don’t recommend specific brands of equipment, I do have a few irrigation product reviews you might want to look at. I try to be as objective as possible and I do present hard facts when I have them (like results from tests on my sprinkler test stand,) but my tests aren’t statistically relevant (I can’t afford to buy and test sprinklers from 30 random stores and random times in order to get a statistically solid sampling.) So the reviews are mostly my personal opinions. If you get 4 industry pros together you will get 4 different opinions of products, each a heartfelt honest opinion. I try to focus on products sold to retail customers at hardware and home stores. I figure other pros aren’t looking for my opinions!
More on selecting your sprinklers is coming later on in the tutorial. At this point in the design process what you need to know is an approximate sprinkler operating pressure. You may have noticed I used the term “operating pressure” here rather than “pressure loss” as previously used for other irrigation equipment like valves and backflow preventers. While pressure loss is a perfectly accurate term for the pressure used by sprinkler heads and emitters, operating pressure is more commonly used. Operating pressure is simply the pressure that needs to be present at the sprinkler or emitter inlet for it to perform as intended.
Manufacturers of sprinklers and emitters provide specifications for each of their products. these specifications typically have a table that lists the operating pressure, the flow the sprinkler will use, and how far the water will spray at that pressure. You will need to obtain these specifications for each of the sprinklers you intend to use. This information may be printed on a label attached to the sprinkler, or on the sprinkler packaging. Most manufacturers also make these specifications available on their web sites. Typically for a sprinkler this specification will list an inlet pressure as pounds per square inch (PSI) and then give a watering radius (feet) and flow rate in gallons per minute (GPM) that will occur at that pressure. A typical table might look like this:
The table above is a sample only, please do not assume these values shown are “typical”. In this sample we can see that at 20 PSI this sprinkler will have a radius of 10 feet and it will consume 2.10 GPM or water flow. Or at 30 PSI this sprinkler will have a radius of 12 feet and it will consume 2.60 GPM or water flow. As you can see a higher water pressure results in a larger radius and higher flow requirement, this relationship between pressure, radius and flow is true of most sprinklers. This is why it is so important to calculate what the water pressure will be when designing. If you design your sprinkler system with the sprinklers 12′ apart you, you would need 30 PSI of pressure at the sprinkler head so that it would spray the required 12′. You would be in big trouble if the pressure lost in pipes and valves resulted in the pressure at the sprinkler only being 20 PSI. You would get a dry area between the sprinklers. This is why it is so important for you to actually go through this whole tutorial and do the design right. (No that spacing is not an error, if the sprinkler radius is 12 feet, then you space the sprinklers 12 feet apart, not 24 feet. More on this later in the tutorial when we discuss sprinkler spacings and placement.) Don’t try to guess or assume “it will work.” I hear from tons of people wanting to know how to fix a system that they just threw together, and now it installed and there are dry spots all over the place. Unfortunately it almost always is very expensive to fix at that point, costing them far more than it would have if they had taken the time to learn how to do it right the first time.
For an emitter the product specification tables would include only operating pressures (PSI) and a flow rate in gallons per hour (GPH) for each of those pressures. (Radius of throw isn’t applicable to drip emitters.)
Can’t find a performance chart or specification for the sprinkler or emitter? Then I would suggest you find another brand and model. Not providing this vital information is an sign of lack of professionalism on the part of the manufacturer. My experience is that most products sold retail without specifications are poor quality “knock off” products, often made by a “copy cat” production plant that makes knock offs of anything they can find with expired patents that will fit into their molding machines. This week they make sprinklers, next week it will be cd cases. They often cut corners like using poor quality raw materials, reducing the amount of plastic in the body and using low quality molds. They are then sold in bulk cheap with no support or guarantee.
Pressure Requirements for Sprinklers
Spray Type Sprinklers, Rotary Nozzles, and Rotators:
For spray type sprinklers, rotary nozzles, and rotators most designers use an operating pressure of 30 PSI, unless a lack of available pressure forces a lower level. The vast majority of spray type heads and rotary nozzles/rotators are designed to operate most efficiently at 30 PSI. Remember that if you use a lower pressure the sprinklers will need to be spaced closer together, because the water won’t spray as far. Check the manufacturer’s performance chart for the sprinkler. Additionally, almost all spray type heads have a radius adjustment screw that allows you to reduce the watering radius for using the sprinkler in smaller areas. (When you adjust the radius using the adjustment screw on a spray head, you are actually reducing the pressure at the nozzle by means of a small valve inside the nozzle. As the pressure is reduced the water doesn’t throw as far, it’s exactly the same as shown on that performance chart, a lower pressure gives less radius.) At pressures above 45 PSI most spray heads start to create lots of mist, which results in poor sprinkler performance. This can also be controlled by using the radius adjustment feature to reduce the pressure. If all the heads are misting a better solution is to throttle the sprinkler zone control valve (cheapest solution) which will reduce the pressure at all the sprinklers on the valve circuit. A better solution is to install a pressure regulator on the mainline to reduce the pressure in the whole sprinkler system, or use special pressure regulating sprinkler heads or nozzles made by some sprinkler manufacturers. Use of these pressure regulators gives more accurate pressures than adjusting a nozzle or throttling a valve, thus they increase the sprinkler system’s efficiency. But they cost a lot more than throttling a valve. If you have a water source with reasonably steady pressure, like most municipal water systems, throttling a valve or adjusting a nozzle will be “good enough” for most people.
Rotor Type Sprinklers:
For rotor type sprinklers the higher the operating pressure the better, within reasonable limits. We don’t want to blow the sprinkler apart with high pressure– and rotors can cause mist too under extreme pressures. As a general rule, most rotor type sprinklers do not work well with less than 30 PSI operating pressure. The optimal pressure is easy to determine for rotors using the following rule, keep reading!
“Stryker’s Rotor Spacing Rule” states that the spacing in feet between rotor-type sprinklers can’t exceed the pressure in PSI at the rotor. So what that means is that if you want to put the rotors 35 feet apart, you rotor will need to operate at 35 PSI or higher, pressure. I like to aim for at least 5 PSI higher than the minimum, so for that 35′ spacing I would aim for 40 PSI.
Important! There is a lot of competition in the sprinkler business to see who can get the greatest radius from a rotor-type sprinkler. Manufacturer’s literature and packaging tends to wildly exaggerate the maximum spacing of rotors. They get those distances by testing the rotors inside a big building with no wind. Even the most gentle breeze will shorten the real-world watering radius (water droplets are very light). If the package says the rotor has a radius of 35 feet at 30 PSI– that all wonderful, but don’t try to install those rotors 35′ apart! In the real world you will not get that distance (unless you are watering inside a building.) If you have 30 PSI do not space the rotors more than 30 feet apart. If you ignore this rule, 9 chances out of 10, you will have dry spots in your lawn! (Yep, over-size ego alert, the rule is named after me. I came up with this rule many, many years ago. So it got my name. That’s how it works!)
Rotor Spacing Example: If you want to space the rotors 30 feet apart then you will need to use a pressure of at least 30 PSI for the rotor. If you want to space rotors 40′ apart you will need 40 PSI for the sprinkler head pressure.
Maximum Rotor Spacing: I don’t recommend spacing sprinklers farther than 55 feet apart unless you have an experienced professional design the sprinkler system. Many tricky problems occur with sprinklers when they are spaced greater than 55 feet apart. Remember that cost is consistent regardless of spacing so it will not save you money. bigger sprinklers cost a lot more money as well as the larger pipe, plus you almost always need a booster pump to get enough water pressure, so you have pumping costs (pumps are expensive to buy, maintain, and operate.)
Most emitters operate best at around 20 PSI. Some emitters are “pressure compensating” which means they should put out approximately the same amount of water over a wide range of inlet pressures. (I’ve found that many pressure compensating emitters are not a whole lot more “pressure compensating” than standard emitters are. Keep in mind that at pressures over 45 PSI emitters may blow apart. Barbed emitters installed in poly tubing may pop out of the tubing at pressures over 30 PSI.
Mix and Match:
Sometimes you need to use sprinklers that require high pressure such as rotors, with sprinklers that use low pressure on the same irrigation system. To do this the system is designed using the pressure requirements of the high pressure sprinklers. The low pressure sprinklers (or emitters) are installed so that a separate valve turns them on and off, and a special pressure reducing valve is used. These valves have a built-in pressure regulation device that reduces the pressure down to the correct amount for the lower pressure sprinklers or drip emitters. Almost all irrigation manufacturer’s now make pressure reducing valves, although you may have to go to a specialty irrigation store to buy them.
If you are working through the Sprinkler Design Tutorial, enter the sprinkler head operating pressure (or the drip emitter pressure if no sprinklers) on the “Sprinkler Heads” line of the Pressure Loss Table.
Remember- the pressure you enter in your table is the pressure for a single sprinkler head. So if you will have 10 sprinklers and they each require 30 PSI you still only write “30 PSI” on your pressure loss table. Also the value you enter should be the highest sprinkler head pressure requirement. So if you plan to use a spray head that will need 20 PSI and also a rotor that will need 35 PSI, you will enter the higher value- which in this case would be 35 PSI. Finally, remember why pencils have erasers. You can always come back and change this value later if you want to! So don’t agonize over it.
A lot of people ask me why you only write down the pressure for a single sprinkler. This is a bit difficult to understand but I will try to explain. I think the easiest way to understand is with a mental image. Think of the water moving through your sprinkler system as millions of water droplets, rather than a single mass of water. On it’s journey through your sprinkler system a single drop of water will loose pressure along the way. Each place where it will lose pressure is one of the items that is listed on your pressure loss table.
Let’s follow a drop of water through a typical sprinkler system! First our water droplet will travel through a pipe from the water company to your water meter. Then it will proceed through the meter into the house supply pipe and on to the irrigation system connection. From there our drop goes into the irrigation system and may pass through a backflow preventer. Onward it travels to the sprinkler zone control valve and through that valve into the lateral pipes leading to the sprinkler heads. Finally the drop goes into one of the sprinkler heads and is propelled out onto the lawn. Note that our droplet only passes through one sprinkler head on the way to the lawn. I’ll bet you’ve never seen water on the lawn jumping back into the sprinkler head so it can go back and try going out through another sprinkler! So it only passes through one sprinkler head. Awwwwwww!!! Starting to make sense, right? Thus we only consider the pressure needed for a single sprinkler head. (O.K. wise guy, yes I have seen water sucked back into a sprinkler head. But that’s not supposed to happen, it means something is wrong with the sprinkler system.) At any rate, even if you still don’t understand why you use the pressure loss for only a single sprinkler, please trust me, it’s correct! I’ve been doing this sprinkler design stuff for over 35 years and have designed thousands of systems. Plus this tutorial has been around since 1997 and successfully used by thousands of people. Plus it is used by dozens of colleges as an irrigation design text.
Still have some questions about sprinklers? Much more information on sprinkler selection is coming later in the tutorial, such as detailed information on the spacing to use between sprinklers and nozzle selection. If you want to jump ahead and check it out, click here. Just don’t forget to use your “back” button to return here!
Bubblers are generally used to flood small areas of the landscape with water. In most cases they are not suitable for lawn irrigation and are used for watering shrubs or sometimes groundcovers. They are most often used to water smaller areas where sprinklers would overspray water out of the area, although there are other specialty uses for them. For example I often use near floor to ceiling windows where I don’t want water spray to drift onto the windows. Bubblers generally need to be in level areas, since they flood water over the ground surface.
Some sprinkler manufacturers make “bubbler nozzles” that fit onto their standard spray-type shrub style or pop-up sprinkler bodies. The classic bubbler is simply screwed directly onto the end of a 1/2″ pipe.
Bubblers and drip emitters: The difference between a bubbler and a drip emitter is flow rate. Drip emitters flow at very low rates, most often 4 gallons per hour (16 liters/hour*) or less. The intent of a drip emitter is that the water would soak into the ground at the emitter location with a minimum amount of water puddling around the emitter. Bubblers flow at higher rates, often measured in gallons per minute rather than hour, and the intent of a bubbler is to flood the ground surface with water.
(*A little optional puzzle for you. Q. If you do the math 4 gallons rounds to 15 liters, so why did I say 16? A. Emitters aren’t designed in English units, they are actually metric. They are designed using liters, so in reality it is a 16 l/h emitter, not a 4 gph emitter. 16 liters rounds to 4 gallons, while 4 gallons rounds to 15 liters. It’s a rounding error issue caused by the unit values rather than bad math. OK, enough fun for the geeks.)
Combining bubblers with sprinklers: Normally bubblers are separated onto a valve circuit of their own so that the watering time can be fine-tuned for exactly how long it takes to flood the desired areas with water. However, a small number of bubblers with adjustable flows can usually be installed on the same valve zone with spray-type sprinklers that are watering adjacent shrubs or groundcovers. Installing bubblers on the same zone wtih spray -type sprinklers is not the most efficient way to go, but as long as it is only 2 or 3 bubblers and they are watering a very small area (not more than 3′ square per bubbler) you can generally play with the bubbler’s flow adjustments and get a reasonably workable watering balance. When watering a larger area using many bubblers or when using non-adjustable flow bubblers you should place the bubblers on a separate valve zone/circuit consisting only of bubblers. Placing bubblers on the same valve zone with rotors or drip irrigation seldom works out well. Do not combine bubblers on the same zone with lawn sprinklers.
There are a number of different types of bubblers available, so let’s start by attempting to group them into some loose categories.
Flood bubblers do just what the name implies, they flood the area around them with water. They further divide into two types, adjustable and non-adjustable.
The adjustable flood bubblers are by far the most common type found, and are what most people think of if they are familiar with bubblers. An adjustable flood bubbler is essentially just a small water valve. It typically has a screw or knob that is used to adjust how much water flows out of it. Most bubblers are designed so that the water gently “bubbles” out of them, the reason being to avoid erosion caused by a strong stream of water. The amount of area they will water is very hard to predict, it depends on how far open the valve is (how much water is coming out), how long it is left on, and the soil type. For purposes of planning your irrigation system, I have found that in most situations flood bubblers will water an area about 3 feet in radius, at a flow of 2 GPM. Understand that this would be a circular 3′ radius area, so if you put them 6′ feet apart that would give you 6′ diameter wet circles that just barely touch each other! In practice if I am watering a long planter strip 3′ wide with shrubs in it I will install flood bubblers 3′ to 4′ apart down the length of the planter. If the area is wider than 3′ I will install a second row of bubblers. Again, bubblers tend to be very hard to predict, you may find you can water a much wider area with a single row, or if you have sandy soil you may have difficulty getting the area flooded with them 3′ apart!
Non-adjustable flood bubblers are just that, non-adjustable. Water flows out of them at a fixed rate. The flow rate depends on the manufacturer, common flows are 1/4 GPM, 1/2 GPM, 1 GPM, and 2 GPM. They are a bit harder to determine spacing for, but that is solved by the intended use. Typically you install one fixed flow bubbler at each shrub or if they are very small shrubs (not more than 18″ – 24″ diameter full grown) you might install 1 non-adjustable bubbler between two shrubs to water both of them. Once again the area watered is very variable depending on which flow rate you choose,how long you run the bubbler, and the soil type. Other than having a non-adjustable flow they are very similar to the adjustable flood bubbler.
A trick you can use is to go to the store and purchase a flood bubbler to use as a test. Also purchase the adapters needed to attach it to the end of a garden hose, it will probably be an odd “Rube Goldbergian” type assortment of adapters and nipples. Install the bubbler on the end of a garden hose, turn it on, adjust the flow, and see how large an area it will flood with water in your yard. To determine the flow you are using for your design, you can measure the flow by using a 1 gallon bucket and seeing how long it takes the bubbler to fill it. 15 seconds to fill is 4 GPM, 22 seconds is 3 GPM, 30 seconds is 2 GPM, 60 seconds is 1 GPM, etc.
Stream bubblers spray a narrow stream of water, most often the stream shoots out 2 to 5 feet from the bubbler. The purpose of stream bubblers is to get the water out away from the bubbler and thus allow watering a larger area with it. In actual practice my experience is that they don’t do a good job of actually flooding a large area. However they are great for watering a group of plants provided the plants are located in the immediate vicinity of where the stream lands. So study the spray pattern of the streams and examine whether the streams will reach the plants you want to water. For example, for large hedges I often will use a stream bubbler that has two opposing streams, one in one direction and a second in the other (called a “center strip” pattern.) I can center one of these between two plants that are 3 to 6′ apart and water both plants with a single bubbler. This is great for large hedges and limited budgets. Keep in mind that foliage will block the spray from a stream bubbler so you may need to trim the plants to keep them out of the bubbler’s spray trajectory. As with other bubblers the area watered by stream bubblers needs to be reasonably level so the water puddles up and doesn’t run off.
I have used lots of stream bubblers on commercial projects where drip irrigating shrubs is impractical due to the high maintenance of most drip systems. These are typically new landscapes where I am designing both the landscape planting and the irrigation system. In this situation I lay out the irrigation system with stream bubblers 36″ apart with the streams adjusted to spray 12″‘. Then I plant the plants at the end of the streams around the bubblers. A full circle stream bubbler typically has 6 streams of water allowing it to water 6 small plants, like daylilies, that are grouped around it. Note that my experience is that this idea doesn’t work as well with larger plants and/or plants placed further than 24″ away from the stream bubbler. If I need additional rows of bubblers I put the rows 24″ apart forming a triangle pattern with the bubblers. Because these are commercial projects where I typically use this stream bubbler layout, I usually use stream bubbler nozzles and install them on 6″ pop-up bodies so they drop to ground level when not running. It looks nicer and it is much safer.
Micro-bubblers are lower flow bubblers often sold as adjustable flow drip emitters. They often have barbs so that they may be installed on poly drip tubing. They are called bubblers because they typically have flows over 4 gallons per hour, which is a higher flow than most soils can absorb without the water pooling on the surface. Although they are adjustable flow, micro-bubbler flows are too low to be compatible with spray or rotor type sprinklers, so don’t put them on the same valve circuit. For more on micro-bubblers see the drip irrigation guidelines tutorial, where they are called adjustable flow emitters.
The path ahead viewed dimly through the fog??? What we’re about to embark on here is known as “doing it the right way”. We are going to start by figuring out what the maximum water supply would be if you had perfect conditions, such as a very short pipe from the water meter to your house, lots of water pressure, a small yard, a happy family, a low interest rate mortgage, and good neighbors! Then we are going to modify that number later in the tutorial to reflect your actual conditions (long pipe, lousy water pressure, bad neighbors, whatever.)
The end result is that we will determine what the exact, optimum water supply is for designing your sprinkler system. What that means for you is that your sprinkler system will use less water, last longer, and there won’t be dry spots! Now it’s going to be a little more work than “guesstimating” would be, but it will be worth it. Don’t get discouraged, be patient, and it will all come together. The worst thing you could do right now is to try deciding what sprinkler you want to use. That would be “putting the cart before the horse”. Trust me, I know what I’m doing. Now let’s get on with it…
A. Find your water supply pipe.
Hopefully you already know where the water service pipe comes onto your property, or at least where it enters your house.
Mild Winter Climates: In milder climate areas there is typically a shut-off valve and or a water meter at the location where the pipe enters the property. From there the pipe generally goes to the house, then surfaces above ground where a house shut-off valve is located, then the pipe turns and runs into the side of the house. Often this location where the pipe enters the house is where the tap for the irrigation system will be made.
Note the “W” etched in the curb in front of the concrete water meter box in the photo above. Often there will be some type of mark on a curb at the location that the water supply pipe to the house runs under it.
The photo above is of a typical mild-climate water supply line where it enters the house. This one has a rather unusual model of pressure regulator (the gizmo with the white adjustment knob on top) to reduce the water pressure. Many houses do not have a pressure regulator. A ball valve (with a blue handle, the handle is in the “off” position) is on the incoming water supply pipe. The pipe going into the wall is the house supply. The pipe exiting the photo at the lower left goes to a hose bib.
Cold Winter Climates: In colder climates the water line often enters directly into the basement or crawl space under the house from underground. This water pipe to the house is often buried very deep to keep it below the frost line. The shut-off valve, and possibly a water meter, are often located in the basement or crawl space to help protect them from freezing.
The photo above shows a typical water supply line in a cold-winter climate. A copper water pipe enters through floor, goes up into a ball valve (yellow handle), then through a pressure regulator, then a remote-reading water meter. You would tap in for the sprinklers after the water meter. The mainline supply size would be measured on the copper pipe coming out of the floor. The water pressure in this case could be measured at any water faucet after the regulator (probably any faucet in the whole house would work). Photo credit and thanks to Ed Pletsch.
What type of pipe is it?
Once you find your supply pipe you need to know what type of pipe or tubing it is. Keep in mind that there may be more than one type of pipe or tubing used at different locations! Often copper is used under concrete slabs and then it converts to PEX for other locations.
Steel Pipe. Steel pipe comes in two types, black steel (used mostly for gas lines) and galvanized steel (galv. steel) which is used for water pipes. Galvanized steel pipe will be a silver gray color, and a magnet will stick to it. It will have threaded joints. Steel pipe is made in conformance with IPS (iron pipe size) standards. Galvanized pipe is often found on homes in inland areas, especially on less expensive tract homes.
Brass Pipe. Brass pipe is sometimes used for homes. Like copper it can take on a greenish tint with age. A magnet will not stick to it. It will have threaded joints. Brass pipe is made in made in conformance with IPS (iron pipe size) standards. Brass is not very common except for short sections of pipe, due to cost.
PVC Pipe. PVC plastic pipe is almost always white or gray, and is more rigid than the other commonly used types of plastic water pipe. Standard PVC pipe is made in conformance with IPS (iron pipe size) standards. It should have the letters “PVC” printed on the pipe. PVC is fairly rigid, and it is not easily scratched with your fingernail. PVC tends to be more commonly used in mild climate areas. Another type of PVC called CPVC is sometimes used inside homes and often is found in older mobile homes. It is similar to regular PVC, but will be labeled “CPVC”. Most often it is a yellowish, gold, or tan color. CPVC in homes is usually made to copper tube sizes (look for “SDR-11” printed on the pipe), but is also sometimes iron pipe size (labeled IPS). PVC is often used for house supply pipes in mild winter areas.
Copper Tube. Copper tube is very common in homes. It takes on a dirty green color as it ages. A magnet will not stick to it. Most joints will be soldered, look for silver color solder at the joints to identify it. Copper tube has a different diameter than iron pipes, and is made in sizes known as CTS (copper tube size). Copper has been the standard “high quality” tube used on better homes for decades. Often used in areas near the coast where salt air causes rapid corrosion of steel.
PEX and PE Tube. Both are both polyethylene (poly) products. Both tend to be used in areas with severe winters and/or rocky soil. There is a lot of confusion over these two poly-based products. Be careful, both are sometimes called “poly”, especially by the sales people in the big home improvement stores. True PEX is a stronger form of cross-linked polyethylene that has become popular in recent years. Both PEX and PE are flexible, and both have a glossy appearance and slick surface. So how do you tell which one you have? Older PE is almost always black, and in most cases PEX is not black. PE is almost never used inside a house if the house was built to code. The surest thing to look for are the letters “PEX” printed on the tubing. Making things even worse, white PEX looks a lot like PVC, especially if it is old or dirty! PEX is easily scratched with a fingernail, PVC scratches, but not easily. PEX was not invented until the ’70s, and it is seldom found in homes built before 1975. (It wasn’t officially sold in the USA until 1985. Of course, if your house has been remodeled, you could still have it in a older house.) PEX is almost always made to conform with CTS sizes. The heavy duty PE tube used for plumbing is most often made to a uniform size standard (labeled “SDR-7”), but many different PE products used for irrigation do not conform with this size standard. Be careful when working with PE tube, if possible take a sample with you when you go shopping for parts so you can test fit them at the store. PEX is quickly becoming the default tube for piping new homes due to low cost and ease of installation.
Warning: PEX pipe has a very thick wall, thus it has a smaller inside area for the water to flow through. This means it has much higher pressure losses when the water passes through it. For this reason you need to be careful when replacing a copper or PE tube with a PEX tube. Often when replacing a copper or PE tube with a PEX tube it is necessary to use PEX that is one size larger than the tube it is replacing. So if you are replacing a 3/4″ copper tube with PEX, you should consider using 1″ size PEX tube for the replacement. Otherwise you may notice a drop in water pressure after the replacement is made.
One good hint to the type of pipe is the way the pipes are connected to each other. PEX and PE are never glued at the joints. Sometimes PEX & PE are heat welded together, but most of the time they are connected together with fittings using clamps, teeth, or compression-nuts that hold the tube onto or into the fitting. (“Fittings” is the term we use for the various connectors that are used to join two or more pipes together.) If the pipe has glued joints it is almost always going to be PVC or ABS. (ABS plastic is typically black rigid pipe, almost always 3″ or larger in diameter, and is mostly used for sewer and drainage pipes. ABS can be other colors so don’t assume a pipe is PVC just because it is white or gray!) Another hint is that poly pipe tends to be used in colder climates, and PVC tends to be used in warmer climates. If you have to regularly shovel snow from the driveway, chances are the pipe is PE or PEX. Copper pipe is often soldered to the fittings. Look for the silver color solder at joints. Steel and brass pipe have threaded connections, a few threads almost always are visible at the joints. Confused yet? Your best bet is to find lettering on the pipe that says what type it is.
B. Find your Water Meter:
Now we need to know if you have a water meter. Most, but not all, water companies use a water meter to measure the amount of water you use. If you don’t have a meter, there will almost always be a shut-off valve at the point your house water line connects to the water provider’s pipes. Often the valves are buried, sometimes several feet down, and a sleeve comes up to the surface with a small lid or box over it. The water company uses a special tool that can reach down and open or close the valve. Often grass has completely grown over the lid and you can’t find it. Try probing the ground with a pitchfork, metal rake, or screwdriver to find the hard cover of the box.
The water meters are normally installed in an underground box as close as possible to the property line. This is usually at the street or alley. Most of the time the box will have “water meter” or the water company name stamped on the lid. In areas with severely cold winters the water meter is often installed in the house basement or a utility room of the house. If you still can’t find it, call your water company and request their assistance.
Try to find a size stamped on the meter. If you can’t find a size, ask your water company or just assume the meter is the next size SMALLER than the pipe running to the house. It is common for the meter to be one size smaller than the pipe. Standard water meter sizes are: 5/8″, 3/4″, 1″, 1 1/2″.
Spiders and snakes: If the meter is in a box, watch out for spiders and ants in the meter box! Most of the “pro” irrigation repair guys I know carry a can of spider spray with them! Sometimes we find snakes, rats, gophers, and other beasts in the boxes too! I found a turtle shell in a box once. No tunnels or holes into the box that I could find. I have no idea how it got in there.
Enter the meter size on your Design Data Form. If you don’t have a meter, enter 0 (zero).
C. Measure Your Water Pressure
Water pressure is the energy that powers your sprinkler system, so it is very important. If you work with it, it will make your sprinklers do the “rain dance”. If you ignore it, it can bite you hard in the wallet! For this tutorial I use the pressure units “PSI” which means “pounds per square inch”. When pros talk about pressure readings we almost never say the words “pounds per square inch”, we just say the letter names “P. S. I”. Outside of the United States pressure is most often measured in “bars”.
First off, grab the phone and call up your water supplier. Ask them for the “static water pressure” for your neighborhood. Don’t be shy, people call them all the time to ask! They may give you a pressure range, like 40-60 PSI. If so, write down the LOW number of this range. You can also measure your own water pressure using a pressure gauge that attaches to a hose bib on your house (you can purchase a 0-120 PSI gauge with a hose adapter on it at pretty much any hardware store).
Pressure regulators (also called pressure reducing valves)
Pressure regulators are devices used to reduce the water pressure and are commonly found on home water supplies in towns with hills. It takes lots of water pressure to lift water uphill. So in order to get the water to the houses on top of the hill the water pressure in the water system has to be very high. But this causes the pressure at the homes at the bottom of the hill to be too high. So pressure regulators are installed on the water supply pipes to homes in the lower areas of town, where the pressures are very high. The pressure regulators are generally set to someplace between 50 and 65 PSI.
If the water company tells you your neighborhood pressure is over 65 PSI, you probably have a pressure regulator installed someplace on the water supply line to the house. The pressure regulator reduces the water pressure in your house, so that it doesn’t damage your plumbing fixtures. Look around and see if you can find it (see the pressure regulators in the pictures above). The regulator may be installed near the water meter or at the point where the water supply pipe enters the house. This is important, because if you have a regulator and you tap into the water supply for your sprinklers after the regulator, the pressure will be a lot lower.
If you have a pressure regulator on your house you must use a gauge to test the water pressure yourself. Most pressure regulators are adjustable, so the water company has no idea what pressure the regulator is set at. When in doubt, test the water pressure with a gauge.
At this point you should make at least a preliminary decision as to where you want to tap into the house water supply pipe for the irrigation system water. Typically, the closer you can tap to the point the water enters your property, the better. Of course, you must tap into the pipe after the water meter. In areas where it gets very cold some people like to tap into a pipe in the basement or someplace else inside a heated building. That way they don’t have to worry about the shut-off valve for the irrigation freezing. (Be sure to install a drain valve after the shut-off valve to drain the water out of the irrigation pipe during freezing weather!) If you have a pressure regulator, consider if it would be better to tap before or after it.
A static water pressure higher than 70 PSI can damage the fixtures and appliances in a household. If you measure a static water pressure higher than 70 PSI when you do your water pressure check as described below, then you should consider installing a pressure regulator on your house water supply if there is not one already. It will help your faucets, pipes, washing machine, dish washer, etc. to all last a lot longer. Make sure it is a good quality brass-body pressure regulator.
For a pressure regulator to work accurately the pressure setting on it must be at least 15 PSI lower than the inlet pressure. So if your static pressure is 70 PSI, the highest pressure you should set on the pressure regulator would be 55 PSI. 55 PSI is a good pressure for both the needs of a house and a sprinkler system.
Hose Bibs as a Water Supply Source = BAD!
Using a hose bib or even a “sprinkler system stub-out pipe” provided on the side of the house for sprinklers is not a good idea. There are often unknown restrictions in the house piping that cause the water supply from these hose bibs to be severely limited. The water running through the house pipes can also be very noisy at night and disturbs some people’s sleep. Do this only as a last resort, when there is no other reasonable way to get water for your sprinkler system. I would suggest you assume the pipe is 1/2″ size, even if it appears larger. If you have concrete that prevents running a new pipe around the house, call a boring contractor and find out how much it would cost to bore a 1″ pipe under the concrete. It may be worth the price. Directional boring technology now allows them to bore and install curved pipes around obstacles.
How to Measure the Water Pressure with a Gauge
Important: If you want to test the pressure yourself, everything that uses water in your home: faucets, ice makers, toilets, etc., MUST be turned off when you take the measurement (that’s why its called “static” water pressure, the water isn’t moving.) Everything! This is critical or you will get a false low reading! You can test the pressure at any faucet that is at about the same height as the proposed irrigation tap. If all the water is turned off, the pressure will be exactly the same regardless of where you test it. (Try it and see!) The easiest place to test the pressure is usually a hose bib or garden valve on the outside wall of the house.
To test the water pressure using a gauge, attach the gauge to a water outlet, like a hose bib or washing machine connection. The place where you attach the gauge can be anywhere in the house, as long as it is about the same height (elevation) as the place where you will tap in the sprinkler system supply. Ie; don’t check it on the 3rd floor if you plan to attach the sprinklers at the first floor! (It is one of those weird, hard to understand hydraulic laws that as long as the water is not flowing the pressure is the same at any point on a pipe that has the same elevation above sea level.) Double check that all the water so water is turned off and not flowing in the house pipes. Then turn on the valve the gauge is connected to and allow the water to enter the gauge. Read the pressure on the gauge. That’s all there is to it, it’s very easy to do! Turn off the water and disconnect the gauge, you’re done!
OK, I realize I may have confused you, because earlier I told you not to use a hose bib to tap the sprinklers into, and now I just told you that you can use a hose bib to measure the static pressure. This is because you can get an accurate pressure measurement from a hose bib– if the water is not flowing, as described. The small pipe can’t restrict the flow if the water isn’t flowing! Confused? Hydraulics is hard to understand. I may sound crazy but I know what I’m doing! Often users of the tutorial have an “ah ha!” moment when they get about 95% done with their first design and suddenly it all makes sense.
The static water pressure that you were given (or you measured with a gauge) is your Design Pressure. Write down the “Design Pressure” on your Design Data Form!
D. Measure the Maximum Available Flow (GPM)
Flow is the traveling companion of water pressure. Pressure is the “energy” that moves the water through the pipes. Flow is the measure of how much water is moved in a given amount of time. Flow is measured in this tutorial using Gallons per Minute (GPM). Other common units used to measure flow include cubic feet per second (commonly used to measure river flows here in the USA), liters per minute, cubic meters per hour, and many others. Now that you know your Design Pressure you need to determine how much water you can use at a time, or your available flow.
Measure Your Supply Pipe Size
You need to find the water supply pipe and measure it’s size. Grab a piece of string about 6″(152mm) long, then find the location where your water supply pipe enters the house. Strip away any insulation, so you can get at the pipe and wrap the string around it. Measure how many inches of string it takes to go around the pipe once.
The string length is the circumference of the pipe (yikes, bad memories of high school geometry!). Using the circumference we can calculate the diameter of the pipe, which allows us to look up the pipe size, from which we can calculate the flow of water using the formula… zzzzzzzzzz….. Let’s forget all those calculations! Based on the string length use the table below to find your pipe size.
For Copper Pipe & PEX Tube
2.75″ (70mm) = 3/4″ pipe
3.53″ (90mm) = 1″ pipe
4.32″ (110mm) = 1¼” pipe
5.10″ (130mm) = 1½” pipe
For Steel, Brass or PVC Plastic Pipe
3.25″ (83mm) = 3/4″ pipe
4.00″(102mm) = 1″ pipe
5.00″(127mm) = 1¼” pipe
6.00″(152mm) = 1½” pipe
For most PE Tube
2.96-3.33″ (75-85mm) = 3/4″ pipe
3.74-4.24″ (95-108mm) = 1″ pipe
4.90-5.57″ (124-141mm) = 1¼” pipe
5.70-6.28″ (145-160mm) = 1½” pipe
Your string length will vary a little, depending on such unavoidable variables as string stretch, dirt on pipe, manufacturing tolerance, what kind of mood you’re in, etc.
Enter the supply pipe size on your Design Data Form! Also make a note of the type– copper, brass, steel, PVC, PEX, or PE.
Find Your Maximum Available GPM:
Your maximum available GPM is the maximum flow of water you have available for your sprinkler system. Actually, it would be more accurate to call this the Maximum Safe GPM. In most cases it is possible to push a higher flow (GPM) through the pipe. However, at high flows the water actually damages the inside of the pipe.
Use the smallest pipe to determine the Maximum Available Flow. Often the water supply coming into your property will not be a single type and size of pipe. You may have a plastic pipe running underground from the water company to your house. When the pipe enters the house it might switch from plastic to copper pipe, or possibly it might be galvanized steel. Then as the water supply pipe runs through the house it likely branches off in several directions with the pipe becoming smaller and smaller in size as it goes. When determining your Maximum Available GPM you will need to check the Maximum Available Flow for each of the types of pipe that the water will pass through, then use the lowest value as the Maximum Available GPM for your sprinkler design. You only need to be concerned about the pipes the water will pass through before it reaches the point where you are going to tap into it for the irrigation system.
There is an exception to the statement above. Often a short section of a smaller pipe size will be present on the water supply for one reason or another. Maybe the plumber didn’t want to drill a larger hole in the wall for the pipe. As long as this smaller pipe section is less than 5 feet long, you can ignore it and use the larger pipe size to determine maximum flow. The higher flow will be able to squeeze through the smaller pipe. The smaller pipe may wear out faster over time, but typically these short pipes are in places where they are easy to replace. Plus, the smaller pipe is often brass or steel, which has a higher resistance to wear than copper or plastic. You have to make a judgement call on this. In most cases I choose to ignore the small section of pipe.
Small Valves. It is not uncommon to find that a shut-off valve installed on the water supply pipe is a smaller size than the pipe. Don’t worry about it. It will not impact the available flow and valves are constructed to handle higher flows than the pipe.
Example 1: You find the water supply pipe entering the house, examine and measure it, and find that it is 1″ copper pipe. But you’re an ambitious type, so you also have done some digging around in the yard and discovered that the pipe going to the house through the yard is 1 1/4″ PE plastic. It just changes to copper about 6 feet away from the house (this is actually a fairly common situation.) After the copper pipe enters the house it quickly branches off in multiple directions and becomes smaller, but this doesn’t matter to you, because you have already decided that you are going to tap your irrigation system into the 1″ copper pipe right where it enters the house. So the irrigation water will not pass through any of those smaller pipes inside the house and you can ignore them.
Looking at the table you find that 1 1/4″ PE gives a flow of 23 GPM. But looking at 1″ copper pipe in the table shows a flow of only 18 GPM. Since the copper pipe is over 5 feet long you can’t just ignore it. This means you must use the lower 18 GPM value. But wait a minute! What if instead of tapping into the copper pipe, you decide to tap into the PE pipe out in the yard before it switches to copper? Now you can use the higher 23 GPM value because the water will no longer go through the 1″ copper pipe!
Example 2: You found you have a 3/4″ copper pipe that comes into the basement but you have no idea where or what type of pipe is used in the yard. It’s 0 degrees outside, and you couldn’t get a shovel into the frozen ground even if you wanted to, which you don’t! In this case it’s reasonably safe to assume the pipe in the yard is 3/4″ copper also. So you would use 11 GPM from the table.
Example 3: You have no idea where the water pipe enters the house, you have no idea where it is in the yard, and you have no desire to try to find out. In this case you must face reality, it’s time to hire a sprinkler contractor!
Maximum Available GPM Table (Maximum Safe GPM)
Maximum Available GPM (Maximum Safe GPM)
PE (poly) Tube
PEX (CTS) Tube
6 GPM(7 ft/sec)
6 GPM(7 ft/sec)
6 GPM(7 ft/sec)
6 GPM(7 ft/sec)
3 GPM(7 ft/sec*)
11 GPM(7 ft/sec)
11 GPM(7 ft/sec)
11 GPM(7 ft/sec)
11 GPM(7 ft/sec)
7 GPM(7 ft/sec*)
18 GPM(7 ft/sec)
18 GPM(7 ft/sec)
18 GPM(7 ft/sec)
18 GPM(7 ft/sec)
12 GPM(7 ft/sec*)
23 GPM(5 ft/sec)
23 GPM(5 ft/sec)
23 GPM(5 ft/sec)
23 GPM(5 ft/sec)
32 GPM(5 ft/sec)
32 GPM(5 ft/sec)
32 GPM(5 ft/sec)
32 GPM(5 ft/sec)
52 GPM(5 ft/sec)
52 GPM(5 ft/sec)
52 GPM(5 ft/sec)
52 GPM(5 ft/sec)
CTS = Copper tubing size.
Caution: The values in the table above are the maximum safe flows for the given size and type of pipe.
These values are NOT the amount of flow you actually will use for your sprinkler system! Step #2 will show you how to modify these values to reflect your actual flow.
Velocities (ft/sec) are shown for reference only.
* PEX tube has an extremely small inside diameter when compared with the other pipe/tube types, this limits flow. Some manufacturers suggest that PEX will not be damaged by higher flows, up to 10 ft/sec. I don’t feel there is sufficient evidence yet to warrant damaging your plumbing by using flows that are too high, so I am sticking with the old industry standard for plastic pipe of 7 ft/sec maximum velocity. If you wish to take the chance, values at 10 ft/sec are
1/2″=6 GPM, 3/4″=11 GPM and 1″=18 GPM. Use these higher values at your own risk. They could cause serious damage to your both your house plumbing & irrigation piping. Read More on Water Hammer.
A flow test is optional, but suggested if you are not positive about the size or type of water supply pipe. The flow test should be run at a faucet as close as possible to the point you will tap into the water pipe for your irrigation system.
Get a 5-gallon bucket. Old paint buckets work great. Since most 5-gallon buckets actually hold more than 5 gallons of water, you will need to calibrate the bucket as follows: Find an accurate measuring container, and measure out 5 gallons of water into your bucket. Then mark the water level on the side of the bucket with a marking pen so you can easily see it. ?The test is simple. Put the bucket under your water outlet pipe and time how long it takes to fill the bucket to 5 gallons. ?The formula for calculating the flow in GPM is: 300 divided by the seconds it takes to fill a 5 gallon bucket = GPM.
If the result of the bucket test is lower than the Maximum Available GPM from the table above, something is restricting the flow. It may be the faucet you are using for the test, or there may be a restriction someplace in the house water supply pipe. You can try to find the restriction and get rid of it, or you can simply use the lower flow test GPM for your Initial Design Flow below.
If the result of the bucket test is higher than the Maximum Available GPM you determined in the table above, use the lower value from the table. The Maximum Available GPM Table gives you the maximum SAFE flow. The bucket test is only used to determine if there is an unseen restriction in the water supply pipe that reduces the flow below the level given in the table. Yes, many sprinkler tutorials and sprinkler salespersons may tell you a bucket test should be used for the design flow, they are wrong! In most cases a bucket test like this one gives you an unsafe flow. See the answers to common questions at the bottom of this page for details on why this happens.
Enter your Maximum Available GPM on your Design Data Form.
E. Initial Design Flow
Your Design Flow is the maximum amount of water you will design your sprinkler system to use. For now, use the same number as the Maximum Available GPM, or use the actual Flow Test GPM, whichever is lower.
You will probably need to reduce your Design Flow later, so additional lines are provided for Adjusted Design Flows on the Design Data Form. The initial flows here are very optimistic, 20 to 30% too high for most situations. You will make the adjustment, if needed, later in step #2. Don’t worry about it now. This is just an advanced warning so you won’t be surprised when you need to change the flow later.
Enter your Design Flow on your Design Data Form. Use a pencil so you can change it later!!!!
F. Do you have enough water available?
You are going to need about 20 GPM of water to irrigate 1 acre of grass with sprinklers. One acre is equal to 43,560 square feet (or 4047 square meters). So if you have a 2 acre grass yard you will need to have 40 GPM of water available in order to water it. If you have shrubs, they typically only use 1/2 as much water as grass, so 20 GPM would water 2 acres of shrubs.
There are only so many hours in the day to water. The amount of water needed varies with the climate, these values are typical for hot summer areas where most sprinkler systems are installed (daily high temperatures over 90 degrees F., 32 degrees C.) These values assume you would be willing to water as many as 10 hours per day. If you are willing to water more hours per day you can increase the area irrigated by a similar percentage.
If you don’t have enough water I can suggest a few ideas for you to look into.
Another option is to use drip irrigation for shrub areas. With drip irrigation you only water the area the plant foliage actually covers. Therefore, if the plants only cover half the actual ground area, you only need half the water.
Consider reducing the amount of lawn and replacing it with shrubs. Shrubs use about half the amount of water as lawn.
Another option for getting a higher flow is to install a larger water supply pipe. A description of how to do that is at the bottom of this page.
Why is the flow you measured with a bucket often too high? The GPM rates in the Maximum Available GPM Table above are based on a SAFE water velocity. When you do the bucket test, there are few restrictions on the flow, so the water velocity may easily exceed that safe limit. If you design your sprinkler system to exceed these flows some really bad things can happen. The first of these is called “water hammer”. Water hammer is a pressure surge which declares its presence by destroying the weakest point in your plumbing. The weakest point is usually that little water tube that runs between the shut off valve and the toilet in your bathroom, or possibly the ones that go to the sink faucets. The result is a flooded house, and that’s something you don’t need. Water hammer is exponentially related to water pressure. The higher the water pressure, the greater the water hammer danger. If your water pressure is over 80 PSI, I suggest that you reduce your maximum flow found in the table above by 20% and read carefully the High Pressure Alert below! The other bad thing that happens at high flows is called “scrubbing”. Scrubbing is what happens when the high water velocity actually scrubs molecules loose from the inside of the pipe. Eventually it wears away enough that the pipe develops a leak. The higher the velocity, the more scrubbing you get. A little scrubbing may take 20-30 years to create a leak. But with a higher velocity the problem becomes much worse. I have seen 7 year old homes need a total replacement of all the copper pipes due to scrubbing damage. This is extremely expensive to repair! In my 30-year-old neighborhood, most of the homes have now had to replace the water supply pipes to the house due to scrubbing damage caused by sprinkler systems installed back in the bad old days before any of us realized the dangers of high flows. There are still a lot of old tutorials and literature being published that were written before the dangers of high flows were discovered, so be careful when comparing advice on this topic. A lot of industry professionals still haven’t gotten the word on this either!
But, but, but… you didn’t hear any water hammer when you did the bucket test, and nothing broke, so what’s the deal? After all, that higher flow could save some serious money on sprinkler parts! The deal is that you are only human. You can’t close the valve fast enough by hand to create water hammer, but don’t worry, an automatic sprinkler valve can! It can snap that valve closed almost instantly. The higher the water pressure, the faster the valve closes. When that valve snaps closed, it sends a shock wave through the pipe (water hammer). It may take weeks or even years for it to wear down the weak point in your plumbing and break. But it will! Then the cost savings on sprinkler parts will seem trivial. Do it right the first time! Water hammer and scrubbing are insidious and relentless. They just keep working away, little by little, day after day. Clunk, clunk, clunk, chew, chew… until the day you come home to a flooded house.
Clunk, clunk, clunk? Pipe noise!!! I hear those loud noises every time the washing machine or dishwasher runs! Is that water hammer??? You bet it is, and you better do something about it! First if the water pressure in your house is over 65 PSI install a pressure regulator to lower the pressure. If that doesn’t get rid of it, go down to your local hardware store and buy a water hammer arrestor. You can get one that screws onto the washing machine or dishwasher fill pipe. They cost about $10-15 and they work pretty well for water hammer caused by appliances. They don’t work nearly as well for water hammer caused by sprinkler systems. This is because many sprinkler systems exceed the maximum water velocities by so much that the arrestor is over-whelmed by it. I’ve written a whole tutorial on this topic: Water Hammer and Air in Pipes.
Q. I need to water a 2.5′ wide by 21′ long grass strip in the middle of my driveway. What is a good method for this narrow an area? My home is located in Southern California.
A. Irrigating lawn in areas less than 4′ wide is very hard and results in a lot of wasted water. It is illegal to install a grass area less than 4 to 6 feet wide in many cities, especially in California and other western States, including ALL of Arizona and most of Nevada (the minimum width varies from town to town.) Enforcement is typically limited to new development, but if you get a permit from the city for the work you may get nailed on this issue.
If you do use sprinklers there is going to be a lot of water waste from over-spray onto the concrete. It will likely run down your driveway and when (not if) the next big drought cycle hits and they start with the “water police” thing you will likely have to stop watering your strip or risk a “fix it” ticket.
If you do use sprinklers you will reduce the radius of each sprinkler to your 30″ width and then you reduce the distance between sprinklers by a similar %. I recommend using side-strip sprays rather than the center-strip type as you will have a lot less over-spray on to the concrete with them. The side strip side are installed down both sides of the strip. Center spray types are installed down the center of the strip. Using center strips type will require half as many sprinklers, but the cost of this initial savings is lousy performance, poor efficiency, and lots of wasted water (it is common when using center strips that 50% or more of the water applied will be wasted.) So let’s say you decide to use 4′ x 12′ pattern side-strip spray nozzles in 4″ pop-up bodies. Since your area is only 30″ wide you would need to reduce the spray width from 48″ to 30″. That would be 62% of 48″ ( 30″ / 48″ = 0.625). So you would also need to reduce the 12′ distance down to 62% also, which is 7.5′ (12′ x 0.62 = 7.44′). So in your 30″ x 21′ area you would space the heads 7′ apart on both sides. After installing the system you would reduce the radius of each head as best you can using the radius reduction screw. It is unlikely you will be able to avoid some over-spray onto the walk as noted earlier. If you decide to use center strip nozzles the procedure and spacing would be the same, there would only be one row of heads, however, installed right down the center of the strip. With center strips you will have to allow more water to overspray onto the cement driveway, if you don’t you will get dry yellow edges. If you want a better explanation of why see this page on sprinkler spacing.
Using Subsurface Drip
Your other option is to use subsurface drip. This is what I would do. In this case I would use three drip tubes running the length of the grass strip. Place one down the middle and the other two should be 4″ in from the edge of the driveway concrete on each side. Use dripperline with 1 gph emitters spaced 12″ apart. Netafim, Rainbird, and Toro all make subsurface dripperline. Make sure the dripperline is a model that the manufacturer claims in their literature is for subsurface installation. Subsurface dripperline uses a different type of emitter designed to keep out dirt and roots. Read my drip guidelines for info on filters and pressure regulators you will need. The salesperson at the irrigation store may tell you that you only need two tubes, which normally would be correct, they typically are spaced 18″ apart, not 12″. There are a couple of reasons I am suggesting 3 tubes rather than 2. First is to get the total flow up because the area is so small and most automatic solenoid valves don’t work very good at really low flows. Another reason is that the concrete on both sides absorbs and radiates a lot of heat, and this is going to make your little lawn strip dry out fast. That’s also why I suggest the dripperlines at the edges of the area be 4″ from the concrete, otherwise the lawn edges right up against the concrete tend to dry up and turn yellow. You are going to need to be careful in selecting your valve, the dripperlines in your 21′ long area are so short that the total flow using 1gph emitters is only going to be 1 GPM; (3 tubes, 20′ long with 1gph emitters every foot. So 20′ x 3 tubes = 60′ of tube. 60′ of tube x 1gph/ft = 60 gph. 1 gpm = 60 gph.) A lot of automatic valves will not work at flows that low. Make sure the rated flow range in the literature for the valve goes that low.
To install your drip system remove the top 5″ of soil from your planter. Now till the soil another 4″ deep. Tamp down the soil to lightly compact it and get rid of air voids. A 8″x8″ hand tamper tool is good for this, you can buy one at any decent garden shop or home improvement store. Now place your dripperline tubes down on top of the soil and use steel erosion control staples to hold the tubes in place. Put a stake every 36″. You can buy the stakes at the irrigation store, they all carry them. The metal stakes work much better than the plastic ones made for drip tube. The stakes are very important, they will rust into the soil and hold the tubes in place. Without them the empty tubes will float to the surface during the winter when the soil becomes saturated during rain storms.
Now put down the final 3″ of soil over the top of the tubes, tamp it down and install your sod (which should be about 1″ thick and should bring the sod surface up even with the top of the concrete.) You will need to lightly hand water the sod for a week or two to keep it cool and moist. It needs time to grow roots down to where the subsurface water from the dripperline is. Slowly back off the hand watering after a couple of weeks. Watch the sod’s color to see how well it is rooting in. If the sod is still in need of top-watering by hand it will turn a dull “flat green” color. When you first install it, the sod will be that dull flat green color because it is stressed from the cutting,shipping and installation. It’s easier to see the color if you stand back and look at it from a distance. Right after you install the sod take a minute to look carefully at it and notice the stressed dull color. Then also note the brighter green color it changes to after you water it the first time it. Now you know what stressed sod looks like and what to look for over the next few weeks. If it is hot or the warm winds are blowing when you install the sod you may need to hand water it more often. Usually watering a couple of times a day is sufficient until the sod is established.
Water-proofing your irrigation system’s wire splices is one of the most critical tasks in any installation or repair that involves wire splices. The splices need to be completely water-proof. Taping them up with electrical tape will NOT work for this! The electrical tape will allow water into the splice as it becomes old, brittle, and the adhesive on it dries out. If you don’t water-proof your splices it WILL cause your valve to fail! Don’t save a buck on a wire splice and ruin a $20 valve! I’ll explain in detail why waterproofing is so important later, first let’s get down to the details on how to make a good waterproof wire splice.
General Things That you Need to Know about all splices!
Caution: The methods described below are intended for low-voltage wires of 24VAC or less, such as those used in typical irrigation system controls. They should not be used for higher voltages.
DO NOT BURY SPLICES directly in the ground. Put a box around them to protect them and to help you find the later. A small plastic utility box works fine. Glue a large steel washer to the bottom of the box lid using epoxy. This will allow you to find the box with a metal detector if grass grows over it. Splices are the most likely place a wire will short out in the future, so a box makes the splices easier to find and repair.
2-wire irrigation systems: These are a newer type of system that uses only 2-wires to control all the valves. The irrigation controller sends a signal through the valves to a decoder at each valve. The decoder then allows power to the valve solenoid only when told to by the controller. These types of systems depend on electrical “signals” sent from the controller through the wire to the decoder. Any voltage leak at a splice can severely impact the signal and cause the system to malfunction. For this reason splices for 2-wire systems need to be made much more carefully. Many of the 2-wire manufacturers have specific splice methods they require be used in order to protect your warranty. Be sure to use these if required!
Not sure if your system is 2-wire? As i write this in 2013, 2-wire systems are seldom used on residential systems, but they are also gaining popularity and will probably start showing up soon, first on larger systems. The controller case normally will be clearly labeled as “2-wire”. A 2-wire system will also have a “decoder unit” installed on the wires at each valve. Standard irrigation control systems have two wires going to each valve. But in a standard system one of the wires goes to a single valve and only that valve. So if you have 4 valves there will be 5 wires (1 common shared by all the valves, + 1 individual wire to each of 4 valves = 5 wires.) On a 2-wire system with 54 valves there would be only 2 wires and each valve would have a decoder unit installed on it. The presence of a decoder to be installed at each valve is the best way to tell if it is 2-wire.
The best way to make the splice is to use special water-proof splice connectors that you can buy at any hardware store. These are made for sealing outdoor wire connections and work very well. There are many different styles and types available.
Water-Proof Twist On Connectors – “Nut” Style or “Wing” Style
Most of the connectors currently used by pros consist of an twist on type wire connector that is filled with a water sealing grease. Sometimes these are called water-proof “nut” or “wing type” connectors. These are inexpensive and very simple to use. Here are general instructions for use since a lot of these inexpensive connectors are sold without instructions. If instructions came with the connectors please use those instructions, as they are intended for the actual connectors you bought!
For every 3 connections you need buy 5 connectors. Why? Because you will probably make several bad splices, and you will have to remove those connectors and toss them in the trash. They can’t be reused because when you remove them a lot of the sealer comes out with the wire. (If you look close most connectors actually say “do not reuse” or similar language on them.)
Start by stripping the insulation off the end of the wires to expose the bare metal wire. Do not strip off too much insulation, the exposed bare wire should be about 1/2 the length of the connector body. You can splice 3 wires together easily using a single connector. It’s OK to put 4 or 5 wires in a connector, but be warned that it gets a lot more difficult getting the wires to stay in the connector when you use more than 3 wires.
Place the bare ends in one hand and using your other hand, align the wires side-by-side, so the ends of the bare sections are lined up together. Those ends need to all go into the connector together at the same time, so hold the wires tight and don’t let them slip out of position. Do not try to insert an additional wire into a wire connector that already has wires spliced together in it. You need to remove all the wires and redo the splice to add more wires.
Push the connector down over the bare ends of the wire. Twist the connector clockwise to screw it on. Hold the wires firmly in position as you twist the connector over them. The connector has threads, a spring, or barbs inside it that will grab the wires and cinch them together tightly as you twist it on. Stop twisting when you feel substantial resistance.
Hold the connector in one hand and tug on each of the wires with the other to make sure the wires are secure and will not pull out. If a wire feels loose or pulls out, disassemble the entire splice and try again. Use a new connector as some of the sealer will probably be lost when you remove the connector, and it needs all the sealer for a good seal. If the wires still pull out after another try you are probably using the wrong size connector.
Finally make a visual inspection of the splice. The insulation on the wire should be fully inserted into the sealer gel or grease. No bare wire should be visible. That’s all there is to using twist on wire connectors, they are very quick and easy.
The connector size is important when using twist on connectors! Be sure you buy and use the correct size connector for the wire sizes you are splicing. The package will list the various wire size combinations that the connector works on. The connector colors indicate the connector’s size and most are standardized. Here are some general guidelines. Warning: There are some brands that do not follow these color guidelines so double check the instructions on the package!
Connectors for #18 wire. Most residential irrigation systems use #18 size wire, this is the size of most of the multi-wire underground irrigation cables sold in hardware stores. Unfortunately the colors for these connectors are not standardized. Most I have seen are dark blue or black. Make sure it says it will connect 2- #18 wires.
Connectors for #14 & #12 wire. Larger irrigation systems and commercial irrigation often use individual #14 wires. Sometimes #12 will be used for irrigation systems with very long distances between the controller and the valve. Most often these connectors are yellow. Note: Most of the yellow connectors I have seen will NOT connect a single #14 wire to a typical valve solenoid wire. For this you will probably need the smaller #18 wire connectors above.
Mechanical Clip Style Non-Stripping Connectors
Clip style is a catch-all name I use for the various types of connectors that use a mechanical clamping system to grab and bite into the wire. Typically with this type of connector you push the wire into a round slot on the connector, and then squeeze some type of clamp that bites into the wire to hold it in place. Some require pliers to squeeze the clamp into the wires. The most popular of these types of connectors for irrigation use is the Blazing Snaploc BVS Series wire connectors and the 3M Scotchlok 314 series connectors. These connectors are more expensive but make a very secure connection almost always on the first attempt. You won’t need to buy nearly as many extras for bad splices.
Container Type Connectors
These connectors are a two piece, two step system. You connect the wires together using either a standard twist type wire connector, a crimp sleeve, or even soldering the wires together. Then you shove the splice into a container filled with a water-proofing grease or jell and snap a retainer lid closed to hold the splice inside the container.
A variation on this type of connector is the original waterproofing method used back when I started in the business. You mixed a 2-part epoxy resin in a small plastic envelope and then shoved the splice into the envelope so it was covered in resin. The resin was allowed to harden creating a solid water-proof seal. Unfortunately the resin was a carcinogen. I don’t think these are sold any longer.
Q. How do I calculate sprinkler risers losses in a sprinkler zone where the risers are extra long, 3 ft or more above ground? I have 10 risers in a zone for my proposed sprinkler irrigation system.
A. If you are using my Sprinkler System Design Tutorial and a standard riser of the recommended size, then you don’t need to worry about pressure lose in the riser, the tutorial has friction loss for the risers built-in to the formulas it uses. So you can ignore the riser pressure loss. Some standard risers are shown on the page on Sprinkler Risers in the Irrigation Installation Tutorial. The recommended size for a riser? In most cases it should be the same size as the threaded inlet on the sprinkler. But please actually read that page on risers, as there are some exceptions to that rule for certain types of standard risers!
OK, I realize that didn’t answer your question, you are asking about a non-standard riser that uses a long pipe to hold the sprinkler high above the ground. In that case you must calculate what the friction loss will be in the longer-than-normal riser pipe. (In this case that would be the 3 ft long pipe you described in your question above.) To do that you simply use the same friction loss spreadsheets that you use to calculate the friction loss in any other pipe. Just use this link to get the proper spreadsheet from my website for the type of pipe you are using. Then open the spreadsheet and on the first line enter the pipe size, GPM of the sprinkler you will install on the riser, and the length of the riser. Enter an error factor of 1.4 rather than the default 1.1. This is because even your “longer” riser is shorter than the typical pipe length that the default error factor is based on. Now read the friction loss. That’s it, you have the friction loss for your non-standard riser! Don’t worry about the fittings like ells and couplings that are part of the riser, that is part of what the error factor is compensating for.
When adding the riser friction loss into the total friction loss calculations for your whole sprinkler system, just add in the loss for a single riser. Use the friction loss value for the riser that has the highest friction loss. (This is most likely the one with the highest GPM sprinkler, or it may be the longest riser if you have different riser lengths. You may have to calculate the friction loss for several different risers to figure out which of them has the highest loss.) Why do you add in the friction loss for only one sprinkler, rather than the combined loss for all of them? Because as a single drop of water goes through the sprinkler system it only goes through one sprinkler, not all of the sprinklers. You have to think about the water as a collection of millions of drops, not as one solid body. So the pressure loss is what a single drop would experience as it travels through the system. As a drop of water enters the sprinkler system it travels through a water meter, lots of pipe, a valve or two, then it finally blows out through a single sprinkler onto the landscape. The pressure loss calculation for the whole sprinkler system is determined by what the worst case pressure loss values would be for a single drop of water traveling through the sprinkler system.
OK, so you calculated the friction loss, but what if it is a really high value, or maybe the calculator complained about the velocity being to high. In this case you need to use a larger size pipe for your riser. For the velocity in a riser you can go all the way up to the 7 ft/sec maximum without too much risk. Velocities in the marginal “use caution” zone are generally OK for risers. High velocity in a riser will seldom cause a water hammer problem, unless you are using a special type of sprinkler that has a solenoid valve built in to it. Those sprinklers are called “valve-in-head sprinklers”, they are very expensive, and are mostly used for golf course greens.
There are a lot of sprinkler head brands and types out there. So how do you decide which one(s) to use? This page will break down the types of heads available and what each type is best suited for. We’ll look at the advantages and disadvantages of each type as well as issues such as brass vs. plastic construction.
To start, sprinklers heads are divided into two types based on the method they use to distribute the water, called spray heads and rotor heads.
More properly called “fixed spray heads” these are the small heads that spray a fan-shaped pattern of water. Think of a shower nozzle. Most use interchangeable nozzles installed on the sprinkler which determine the pattern (1/2 circle, full circle, etc.) and the radius of the water throw. Some specialty patterns are available for long, narrow areas. Spray heads are spaced up to 18 feet apart. There are some brands that promote radii up to 20 feet, but I’ve had really poor experiences with those. Spray heads need between 20 and 30 PSI of water pressure to operate properly so they are the best choice if you have low water pressure.
Rotor sprinkler heads, often just called “rotors”, is the term used to describe the various sprinklers which operate by rotating streams of water back and forth over the landscape. The example which most people are familiar with is the “impact” rotor sprinkler (often improperly called a “rainbird*”) which moves back and forth firing bursts of water. You probably know this sprinkler best for the distinct sound it makes when operating– tooka, tooka, tooka, tic, tic, tic, tic, tic, tooka, tooka, tooka, etc… The impact rotors are rapidly being replaced now by gear driven rotors which are much quieter, lower maintenance, and much smaller in size. These gear-drive rotors have one or more fingers of water which move silently across the landscape. The prettiest of these are the “multi-stream rotors” where multiple streams of water rotate over the landscape one after the other like rotating spider legs. Rotors can be spaced from 15 feet to 65 feet apart. There are rotors available that can be spaced farther apart than 65 feet but I don’t advise using them in most situations, even golf courses are moving away from using them due to problems. Most rotors require a lot more water pressure to operate than spray heads. Here’s a rule of thumb, “The water pressure at the rotor head in (PSI) must exceed the distance (feet) between the heads.” (Known as Stryker’s Rule, admittedly that’s a little ego stroking on my part, but I really did write the rule!) Thus if you want to space rotors 35 feet apart you will need 35 PSI of pressure at the rotor. More on this later. The small rotors most often used for residences work best at 25 to 35 foot spacings.
Note: If you have chosen to use the Prescriptive Standard the maximum spacing you can have between rotors will be 30 feet. This is due to the 30 PSI sprinkler pressure used by the Prescriptive Standard.
* Rain Bird® is the name of a sprinkler company and is a registered trademark. The Rain Bird company makes many different types of sprinkler heads, including impact rotors. They also make a full line of other irrigation products.
Rotary Nozzles: A new type of miniature rotor has been introduced in recent years. These are often called rotary nozzles. The first brand on the market was called the “MP Rotator”, and several other similar products quickly became available from other companies. Rotary nozzles are a very small turbine-driven rotor mechanism that is the same size as the standard nozzle on a spray-type sprinkler. Thus they can be installed onto the smaller, and less expensive, spray head pop-up bodies. These rotary nozzles have a radius generally between 15 and 30 feet. The exact distance depends on the model. They all use multiple streams of water that rotate around the nozzle and look like rotating spider legs. Some research indicates these rotary nozzles are more efficient than standard spray heads and result in lower water use. So far they have performed well overall, but beware of recently introduced models as this is tricky technology and new products may have a lot of “bugs”.
Guide to Selecting the Right Sprinkler Type:
Which to use, sprays, rotary nozzles, or rotors? Here are some questions to guide your selection.
Is your water pressure less than 45 PSI static? If so you should consider using sprays or rotary nozzles.
Is the area less than 16 feet wide? Then you should consider sprays or short radius rotary nozzles.
Areas between 16′ and 25′ wide are good candidates for using rotary nozzles.
If the area you want to water is greater than 25′ x 30′ in dimension standard rotors are likely the best solution.
Is the edge of the area to be watered curved? If the edge has sharp curves (less than 20′ radius) then rotors will have difficulty watering the edges without over spraying them. This may not be an issue depending on what is beyond the edge. If the area beyond the edge should not get water on it (like a sidewalk, patio, driveway, road, or structure) you might want to consider a smaller rotary nozzle or spray-type sprinkler.
Installation Issues related to Head Selection:
Rotors are spaced farther apart and require less pipe and trenches, but they also cost much more per sprinkler. Systems that use rotors, and to a lesser extent rotary nozzles, are easier to install due to less trenches to dig and back fill.
Cost Issues in Selecting Type of Sprinkler:
Surprisingly, regardless of the type of sprinkler you use, the cost per square foot of area irrigated comes out about the same (assuming proper design.) When using rotors there is less pipe and trenches, but the rotors themselves cost more. Spray heads are less expensive to buy, but they require more pipe, more trenches (labor cost), and more valves. In the end, the price really comes out pretty close either way.
Note: If your “design pressure” is less than 40 PSI standard rotors will not work properly, DO NOT USE THEM. (That’s Design Pressure, not the pressure at the sprinkler head.) See the section “Measure Your Water Supply“. If you have a well and pump you must have your pump-on setting adjusted to no less than 40 PSI if you plan to use rotors. A “40-60” setting is typical. Contact your pump company for assistance.
If you are unsure, try using rotors in your design. If they don’t work out well, then erase them from your plan and try rotary nozzles. In may situations the best option may be to use rotors in the large areas, and spray heads or rotary nozzles in smaller or more narrow spaces. So you may have a mixture. This is OK, but there are some things you need to be careful of when mixing different types of sprinklers. The first is that each type must be on a separate valve circuit. More on this later in the tutorial. The second is determining how to space the heads where they meet each other. For example, if you have a 30′ radius rotor next to a 15′ radius spray head, how far apart should they be from each other? There are many different schools of thought on this, but my general recommendation is to split the difference. In this example put them 22′ apart. Yes, the rotor would over-shoot the spray head by a considerable distance. But if you put them 30′ apart you will get a distinct dry spot between them.
Basic Body Styles:
Pop-Up Style Sprinklers:
Pop-up style sprinklers are installed with the sprinkler body below ground. A portion of the sprinkler, appropriately called the “riser”, rises up out of the ground when the sprinkler is operating and then retracts back below ground when not in use.
Shrub Style Sprinklers:
Shrub style sprinklers are installed above ground on top of a section of pipe. Read the warning below!
Which style to choose? In most cases you will want to use pop-up style heads, even in shrub areas. Pop-up sprinklers are more expensive to buy, but with shrub sprinklers you also need to include the cost of the extra section of pipe needed to hold the shrub sprinkler above ground. In fact, in recent years mass production of popup style sprinklers has lowered their price, while increases in pipe costs have made shrub style sprinklers overall more expensive.
Many people are injured each year when they trip over, or fall onto, shrub style sprinklers. For shrub and ground cover areas pop-up sprinklers are available with pop-up heights of 3″, 4″, 6″ and 12″ above ground. A few brands are available with lower pop-up heights, but be warned that lower heights often cause problems. I recommend that you not use any sprinkler that pops up less than 3″. As a general rule it is best to also avoid shrub style sprinklers unless a very tall riser is needed to raise the sprinkler spray over the tops of tall shrubs. When needed, shrub style sprinklers should only be used in areas well away from sidewalks, patios, and areas where children play.
Metal or Plastic?
The conventional wisdom is that metal is more durable than plastic, and therefore is better. Up until the late 1970’s metal (usually brass, sometimes zinc) was the standard material from which almost all sprinklers were made. However, times have changed and now plastic is the most common material for sprinklers. Very few manufacturers even bother to make an all-metal sprinkler anymore. The primary reason for this change in materials is cost; machined metal parts are enormously expensive in comparison to injection molded plastic. Fortunately, most of today’s plastic sprinkler heads are very well engineered and perform better than the old metal sprinklers.
Hybrids: A few companies manufacture plastic sprinkler bodies which accept brass nozzles, which they claim results in a better water pattern. Other manufacturers claim that plastic nozzles perform as well as brass. The research tends to indicate that a really well-machined brass nozzle has better water distribution. But that’s laboratory tests, and in the real world a lot of other factors come into play. I personally haven’t noticed any significant difference in performance between most brass and plastic nozzles in well-designed, sprinkler systems, although brass nozzles will no doubt last longer. More importantly, there are a few nozzles, both brass and plastic, which don’t seem to perform as well as others. Fortunately, they are easily identified by comparing prices (as in “you get what you pay for.”) Typically these bad nozzles come pre-installed on sprinklers that don’t have the features I list below, so if you stick to sprinklers with my recommended features you will get acceptable quality nozzles.
Features to Look For:
The following features are common to all good-quality sprinkler heads (for both rotors and spray type heads). Choosing a sprinkler without these features is asking for trouble.
Spring Retraction: Make sure a spring is used to pull the pop-up riser (sometimes called a “piston”) down into the case when the sprinkler isn’t on. As a general rule the stronger the spring, the less likely the riser is to “stick up”. Don’t worry about the spring being too strong, or creating too much “resistance” that might hurt the sprinkler performance. The sprinkler is designed to compensate for that. Stay away from sprinklers that rely only on gravity to retract the pop-up riser.
Wiper Seal: This is a soft plastic seal around the pop-up riser stem that seals the riser so it won’t leak . The wiper seal also is responsible for keeping dirt out of the sprinkler body, and is the most important part in determining how long the sprinkler will last. Make sure the sprinkler model you select has a wiper seal. Note: on some sprinklers you must remove the sprinkler’s cap and look inside the bottom of it to see the seal. Be careful when removing the cap, hold both the cap and body tightly! On some models the spring will shoot out!
Screens: A screen inside the sprinkler helps protect it from getting messed up by junk in the water. Consider this screen to be a back up filter to catch stuff that might have gotten into pipes when making repairs. These in-sprinkler filters quickly become clogged if the water is even remotely dirty. You should still have a good quality water filter at the water source upstream of the valves.
3 Inch Pop-Up Height (or higher):Unless you just like to trim grass around sprinkler heads, make sure the pop-up height is 3″ or more. This way the spray nozzle will clear the top of the grass. Most professionals use 4″ pop-up sprinklers in lawn areas, and 6″ or 12″ pop-ups in shrub areas.
Check valve: This feature is optional, but I highly recommend it. Sometimes these are called “anti-drain valves”. The built-in check valve keeps the water from draining out of the pipes through the sprinkler head each time the valve circuit is turned off. Check valves save water, obviously, since they keep the water trapped inside the pipes. But there are other advantages as well. They reduce muddy areas around the heads that are caused by the water slowly draining out. Since the water stays in the pipes the sprinklers come on faster and work more efficiently. If the water has drained out of the pipes, then each time you turn on the sprinklers the sprinklers will spit and spew air as the pipes refill. As the water quickly fills the pipes it slams into the fittings (bends and turns in the pipe) and then into the bottom of the sprinkler heads. This causes a lot of stress on the pipe and sprinklers and can result in premature failure. So there are a lot of good reasons for getting sprinklers with built in check valves. These check valves are nothing more than a rubber washer on the bottom of the sprinkler riser stem. You can easily remove them if needed. They are so cheap for manufacturer’s to make that I really think they should be standard equipment on all sprinklers! One final note on check valves. In cold season areas where it is necessary to drain the water from the system to prevent freeze damage the check valves will prevent the water fro draining out. You must either remove the check valves in the cold season, or use compressed air to blow the water out of the pipes. Most people blow out the pipes.
Other Sprinkler Features:
Pressure regulators: Generally this feature is not necessary with a well-designed system. Pressure regulation can be done at the valve or water source and will provide more benefits when done at those locations as opposed to regulating it at the sprinkler. These built-in pressure regulators provide a constant pressure at the sprinkler nozzle, which creates more uniform water coverage. There is a catch however, a pressure regulator can only decrease the water pressure, it can’t increase it. So it is only useful if your water pressure is already too high. In the industry this feature is known as a “spec item”. It is a gold-plate option that is sold primarily to landscape architects and municipalities for projects with high budgets. My opinion is that pressure regulators in sprinklers are a device that 90% of the time is used to correct for poor design practices. I have often seen systems that use these pressure regulators and then add a booster pump to create enough pressure for them to work. That is like buying a economy car and then towing it around with a truck so that it will get better mileage! Another legitimate use for the pressure regulators is that if the nozzle breaks off of the sprinkler the pressure regulator will limit the size of the geyser produced, and thereby save water. While true, I question the expense to benefit ratio of this solution. Plus it only saves water if the nozzle comes off. If the whole sprinkler breaks off (just as common a problem) then it saves no water at all. Warning: if you have low water pressure, a built-in pressure regulator will seriously harm performance of the sprinkler. They should only be used with systems that have excess water pressure. When using a built-in pressure regulator increase the pressure requirement of the sprinkler by 2 PSI. This is because pressure is lost as the water goes through the pressure regulating device. So if the sprinkler performance chart says 30 PSI you should increase that by 2 PSI to 32 PSI.
Pressure Compensating Screens and Nozzle Inserts: In high pressure situations these will reduce sprinkler misting and improve efficiency. These are different from the pressure regulators built into the sprinkler bodies, these are not as accurate as the regulators. They work different and, while not perfect, they actually work pretty well. The pressure compensators are small rubber discs with a hole in them, color coded for specific flow rates. Like the pressure regulators they will not increase the water pressure, so if you don’t have enough pressure they are not going to help you at all. However, unlike the pressure regulators built into the bodies they do not require you to add 2 PI to the sprinkler pressure required. This is because each one is made for a specific flow. But one of the best uses for these is to reduce the radius of spray type sprinklers, using them in place of using the radius adjustment screw on the nozzle. To figure out which pressure compensating insert to use for the radius you want you will need to consult a reference chart supplied by the manufacturer. The advantage to using these pressure compensating screens/nozzle inserts is that they hold the radius adjustment constant, regardless of temperature. The radius adjustment screws that are built into spray head nozzles are notoriously fickle, when you use them to reduce the radius, as the water and air temperature change so will the radius. This is because the screw acts as a valve, to reduce the radius you turn the screw and this reduces the flow through the nozzle. So if you want to reduce the radius you would turn the screw, which then reduces the size of the opening the water flows through. The problem is that as the temperature gets warmer this screw expands and as it expands it throttles the flow even more. This causes the radius to be reduced. Often in hot weather the radius adjustment screw will expand so much that it will completely shut off the flow of water! That will not happen when you use these pressure compensating screens to reduce the radius.
Ratcheting Risers: Almost all pop-up sprinklers now have ratcheting risers as a standard feature. The ratcheting riser allows the riser stem to be twisted to align the direction of the water spray.
Side Inlets: Side inlets allow the pipe to be attached to the side of the sprinkler. This allows for shallower installation of the pipe and can save labor during installation. The problem with side inlets is that when you use the side inlet on most sprinklers the built-in check valves do not work. Also if you plan to “winterize” your sprinkler system by blowing it out with air the use of side inlets can make it very difficult, sometimes impossible, to get all the water out of the sprinklers. Most sprinklers that have side inlets have both a bottom and side inlet. They come with a plug installed in the side inlet, to use the side inlet you remove the plug and place it in the bottom inlet. The problems listed above only occur if you use the side inlet.
Shut-Off Devices: These devices generally fit under the sprinkler nozzle and shut off the flow if the nozzle is removed or comes off. Another “spec item.” For most people these will offer little or no value. They save water if the nozzle comes off, but that seldom occurs. Depending on the design of the shut-off device they might also stop flow if a riser sticks up and is mowed off. Some are located near the top of the riser, so it is likely they would be mowed off along with the riser, thus providing no benefit.
Sprinkler Make and Model Recommendations:
The most common question I get from users of this tutorial is “what do you think of the ABC model sprinkler made by XYZ sprinkler company”. Would I risk making the major sprinkler manufacturer’s mad by publishing that kind of information? Of course! See my irrigation product reviews.
More on selecting your sprinklers is coming later on in the tutorial. For now lets just get an operating pressure. The first thing you may have noticed is that I used the term “operating pressure” here rather than “pressure loss” as previously. While pressure loss is a perfectly accurate term for the pressure used by sprinkler heads and emitters, operating pressure is more commonly used. Operating pressure is simply the pressure that needs to be present at the sprinkler or emitter inlet for it to perform as intended.
Manufacturers of sprinklers and emitters provide specifications for each of their products that list the various acceptable operating pressures for the units and how they will perform at that pressure. You will need to obtain the specifications for the products you intend to use. You may find this information printed on the sprinkler box or you may need to request it from your supplier. Most manufacturers also make specifications available on their web sites. Typically for a sprinkler this specification will list an inlet pressure as pounds per square inch (PSI) and then give a watering radius (feet) and flow rate in gallons per minute (GPM) that will occur at that pressure.
For an emitter the information would include only operating pressures (PSI) and a flow rate in gallons per hour (GPH) for each of those pressures. (Radius of throw isn’t applicable to drip emitters.)
Pressure Requirements for Sprinklers
Spray Type Sprinklers:
For spray type sprinklers most designers use an operating pressure of 30 PSI, unless a lack of available pressure forces a lower level. Remember that if you use a lower pressure the sprinklers will need to be spaced closer together, because the water won’t spray as far. Sprinkler manufacturers provide charts that tell you how much pressure is required for the sprinkler and how far it will spray with that pressure. Look on the package for the chart. Additionally, almost all spray type heads have a radius adjustment screw that allows you to adjust the watering radius down for smaller areas. (When you adjust the radius using the adjustment screw on a spray head, you are actually reducing the pressure at the nozzle by means of a small valve under the nozzle. The reduced pressure results in a decreased radius of throw.) At pressures above 45 PSI most spray heads start to create lots of mist, which results in poor irrigation. This can be controlled by using the radius adjustment feature to reduce the pressure, partially closing the valve to reduce the pressure, installing a pressure regulator on the mainline to reduce the pressure, or by using special pressure regulating nozzles made by some sprinkler manufacturers (which, you guessed it, reduce the pressure!
Rotor Type Sprinklers:
For rotor type sprinklers the higher the operating pressure the better. (O.K., within reason. We don’t want to blow the sprinkler apart with high pressure– and rotors can cause mist too under extreme pressures.) But as a general rule, most rotor type sprinklers do not work well with less than 30 PSI operating pressure. Keep reading!
“Stryker’s Rotor Spacing Rule” states that the spacing in feet between rotor-type sprinklers can’t exceed the pressure in PSI at the rotor. There is a lot of competition in the sprinkler business to see who can get the most radius from a rotor-type sprinkler. Manufacturer’s literature and packaging tends to wildly exaggerate the maximum spacing of rotors. They get those distances by testing the rotors inside a big building with no wind. Even the most gentle breeze will shorten the real-world watering radius (water droplets are very light). If the package says the rotor has a radius of 35 feet at 30 PSI– DO NOT BELIEVE IT! In the real world you will not get that distance. If you have 30 PSI do not space the rotors more than 30 feet apart. If you ignore this rule, 9 chances out of 10, you will have dry spots in your lawn! (Yep, over-size ego alert, it’s my rule, thus the name.)
Rotor Spacing Example: If you want to space the rotors 30 feet apart then you will need to use a pressure of at least 30 PSI for the rotor. If you want to space rotors 40′ apart you will need 40 PSI for the sprinkler head pressure. I don’t recommend spacing sprinklers farther than 55 feet apart unless you have an experienced professional design the sprinkler system. Many tricky problems occur with sprinklers when they are spaced greater than 55 feet apart.
Most emitters operate best at around 20 PSI. Some emitters are “pressure compensating” which means they should put out approximately the same amount of water over a wide range of inlet pressures. (I’ve found that many pressure compensating emitters are not a whole lot more “pressure compensating” than standard emitters are. Keep in mind that at pressures over 45 PSI emitters may blow apart. Barbed emitters in poly tubing may pop out of the tubing at 30 PSI.
Mix and Match:
Sometimes you need to use sprinklers that require high pressure such as rotors, with sprinklers that use low pressure on the same irrigation system. To do this the system is designed using the pressure requirements of the high pressure sprinklers. The low pressure sprinklers (or emitters) are installed so that a separate valve turns them on and off, and a special pressure reducing valve is used. This valve reduces the pressure down to the correct amount for the low pressure sprinklers. Almost all irrigation manufacturer’s now make pressure reducing valves, although you may have to go to a specialty irrigation store to get them.
Quick “Prescriptive Standard” Set Up:
For the Prescriptive Standard use 30 PSI for the sprinkler pressure. Do not space rotor heads more than 30 feet apart when using the Prescriptive Standard!
Enter the sprinkler head operating pressure (or the drip emitter pressure if no sprinklers) on the “Sprinkler Heads” line of the Pressure Loss Table.
Remember- the pressure you enter in your table is the pressure for a single sprinkler head. So if you will have 10 sprinklers and they each require 30 PSI you still only write”30 PSI” on your pressure loss table. Also the value you enter should be the highest sprinkler head pressure requirement. So if you plan to use a spray head that will need 20 PSI and also a rotor that will need 35 PSI, you will enter the higher value- which in this case would be 35 PSI. Finally, remember why pencils have erasers. You can always come back and change this value later if you want to! So don’t agonize over it.
A lot of people ask why we only write down the pressure for a single sprinkler. This is a bit difficult to understand but I will try to explain. I think the easiest way to understand is with a mental image. Think of the water moving through your sprinkler system as millions of water droplets, rather than a single mass of water. On it’s journey through your sprinkler system a single drop of water will loose pressure along the way. Each place where it will lose pressure is one of the items on your pressure loss table. Let’s go along for the ride. First our water droplet will travel through a pipe from the water company to your water meter. Then it will proceed through the meter into the house supply pipe and on to the irrigation system connection. From there our drop goes into the irrigation system and may pass through a backflow preventer. Onward it travels to the valve and through the valve into the lateral pipes leading to the sprinkler heads. Finally the drop goes into one of the sprinkler heads and is propelled out onto the lawn. Note that our droplet only passes through one sprinkler head on the way to the lawn. I’ll bet you’ve never seen water on the lawn jumping back into the sprinkler head so it can go back and try going out through another sprinkler! So it can only pass through one sprinkler head. Thus we only consider the pressure needed for a single sprinkler head. (O.K. smart guy, yes I have seen water sucked back into a sprinkler head. But that’s not supposed to happen, it means something is wrong with the sprinkler system.) At any rate, even if you still don’t understand why you use the pressure loss for only a single sprinkler, please trust me, it’s correct!
Much more information on sprinkler selection is coming later in the tutorial, such as spacing and nozzle selection. If you want to jump ahead and check it out, click here. Just don’t forget to use your “back” button to return here!
PVC pipe types labeled “schedule” (abbreviated “SCH“) are made based on the traditional dimensions used for steel pipe. Unfortunately steel has very different strength characteristics from plastic, so it is a system that isn’t very logical for use with PVC pipe. But when plastic first came along it was made to the same size standards that were already in use for steel. The common PVC pipe schedules you will see in stores are SCH 40 and SCH 80. As the pipe sizes rated SCH increase, the strength and pressure rating of SCH pipe decreases. So 1/2″ SCH 40 PVC pipe is very strong, while 2″ SCH 40 PVC has comparatively a low pressure rating, and is more easily damaged. In sizes 1/2″ to 1 1/2” SCH 40 is a thick wall pipe with a reasonably high pressure rating and good resistance to physical damage. It is often used for mainlines and other situations where a tough high pressure pipe is needed. Sch 80 is generally used for making threaded plastic nipples because the plastic walls are thick enough to have threads cut into them (although most now have molded threads rather than threads “cut” with a die.)
As you can see, the pressure ratings drop as the pipe size increases. Note that the industry standard rule is that your normal operating pressure should not exceed 1/2 of the rated pipe pressure. In other words, you shouldn’t use 1 1/2″ pipe for pressures higher than 165 PSI (330 x 0.5 = 165 PSI). This is because pressure surges created by closing valves can easily double the water pressure in the pipe. This rule applies to all PVC pipe, including that labeled SCH and CL.
Class rated pipe
PVC pipe types labeled “Class” (abbreviated “CL“) are based on the pipe’s pressure rating. So Cl 200 PVC pipe is rated for 200 PSI of water pressure. Cl 315 PVC pipe is rated for 315 PSI of water pressure. The strength of CL labeled pipe is directly related to the pressure rating. The standard “Cl” pipes are Cl 125, Cl 160, Cl 200 and Cl 315. Of these Cl 200 and Cl 315 are most common. Cl 125 is sold as a low cost pipe for use in sprinkler laterals for those for whom low price is everything. It has a very thin wall and breaks easily if not handled carefully or nicked with a digging tool.
1/2″ size pipe is generally only available in SCH 40. This is because of the thin wall of 1/2″ pipe makes it very easy to break. I don’t recommend using 1/2″ PVC pipe at all, however if you must, you should use SCH 40. Sometimes you will find 1/2″ Cl 125 PVC pipe at discount stores due to the very low price.
The Class system is obviously a more logical system for labeling pipe as you know immediately how strong the pipe is based on the label. Unfortunately the more confusing “SCH” system became entrenched in the industry and remains.
What Pipe Type to Use
All PVC pipe labeled for a given size in the USA has the same outside diameter. So any pipe labeled as 3/4″ will be the same diameter, whether it is SCH 40 or Cl 200 or any other type. That allows the same fittings to be used to join the various pipe types together. Most fittings are made to SCH 40 standards, although SCH 80 fittings are available, typically only at specialty plumbing and irrigation stores. Technically most codes require SCH 80 fittings for pipe sizes 2″ or over. In practice I’ve noticed that SCH 40 fittings are often used up to 3″ size. When dealing with sizes 4″ and above the use of non-glued “rubber ring-joint” fittings is recommended and usually required by code as well. Glueing joints on 3″ and larger PVC pipe is very, very difficult.
“Mainlines” are all of the pipes that are under constant pressure, that is, the pipes that are before the sprinkler zone valves. In most of the industry SCH 40 PVC pipe is used for irrigation mainlines up to 1 1/2″ size. For 2″ size and larger Cl 315 PVC is used. Most building codes prohibit the use of 2″ and larger SCH 40 PVC pipe for pressurized water lines. Depending on the jurisdiction, this rule may or may not be applied to irrigation systems. Those same codes generally require that all pressurized PVC pipes (mainlines) be buried at least 18″ deep to protect them from accidental damage, regardless of the type or size of pipe used.
“Lateral” pipes are the pipes after the sprinkler zone valve. These pipes are only pressurized when the sprinklers are operating. For lateral pipes the standard is to use Cl 200 PVC pipe. Where budget is a concern and you can find it, sometimes Cl 160 is used. As previously mentioned I recommend you avoid Cl 125 PVC pipe. Laterals can be buried any depth, but I generally recommend at least 10″ deep to avoid a lot of maintenance problems with broken pipes.
Q. I am currently in the process of converting my entire lawn irrigation system into an electronically controlled system using a control and relay setup for the pumps. I currently have two centrifugal pumps that pump water from a pond about 150 yards away. The system has seventeen zones and I have already ordered all the valves needed as well as the controller and pump relay and am in the process of installing it all. I am concerned with the fact that if one of the valves fail to open then I may have a problem with too much pressure and would like to know what kind of setup you suggest in order to overcome this. I researched pressure relieve valves and such but I feel that a flow sensor combined with a high pressure sensor to turn the pumps off would be the safest route in order to minimize damage to the pumps. How could this be done to cut pumps off if there is too much pressure or no flow at all?
A. They make flow sensors that use paddle wheels, they can actually measure the flow rate in the pipes in GPM or cu ft/min. They are a great way to go for this. They require that you have a fancy irrigation controller that can work with them, so you may need to return your controller and upgrade it. The irrigation controller measures the flow and compares it to the pre-programmed flow that should be present in the system for the valve that is currently open. The controller then makes a decision based on that flow. If the flow is too low or too high it can shut down the pumps or close a master valve that shuts off the water to the entire system.
The sensor needs to be installed in a tee on a straight length of pipe. The length of the straight pipe should be 5x the pipe diameter before the sensor and 5x after it. This is to reduce water turbulence in the pipe caused by turns, the turbulence can cause inaccurate pressure readings.
You can also use a pressure sensor and pump logic controller to turn off the pumps at high pressure or very low pressure. You should be able to get what you need at a specialty pump supplier. The sensor is a bit different from the typical pressure switch. A standard switch turns the pump on at low pressure and off at high pressure. The logic controller is basically used as a detector and timer. The timer would only turn off the pump if the high pressure was present for maybe 4 minutes or so. It is normal to have a pressure spike as the system changes from one valve to another, you don’t want the pump to shut off during the switch of valve zones. You also need a delay to allow the pump to start up, since there will be no pressure until it gets going (so the switch would never allow the pump to start!) The pressure sensor also needs to be on a straight pipe section like the flow sensor.
If you wnat to use a pressure sensor you should also do a quick test to make sure your pumps are capable of producing a high enough pressure to detect. Some pumps don’t produce very much increased pressure, even at no flow. So you need to make sure your pump will, if it doesn’t you need to use a different method of detecting no flow, like a flow sensor. Run the pump as normal with the smallest valve circuit open and check the pressure. Now shut off the valve and watch the pressure (don’t let it run for more than 3-4 minutes without flow! Don’t want to overheat the pump.) Ideally you want to see a pressure increase of 5 or more psi. The more pressure increase you have the less likely you are to get a false alarm caused by a small pressure spike.
If the pump doesn’t produce enough pressure to measure the increase at no flow you will need to use a flow switch to detect flow. A flow switch is nothing more than a paddle that sticks down into the pipe. When the water is flowing it presses against the paddle and the switch opens/closes (depending on how you have it set.) It’s very simple. Unfortunately flow switches also break pretty easy, so they have to be frequently replaced. That’s why I don’t use them as my first choice.
The area watered by each sprinkler must overlap substantially the area watered by the adjacent sprinkler. This overlap may seem like a waste at first, but it is a very important necessity. Without this overlap it would be impossible to design sprinkler systems that provided uniform water coverage.
Have Doubts? See for yourself, it only takes a couple of minutes to prove! Grab a piece of paper and draw circles on it so that all areas of the paper are inside a circle, but no circles overlap. You can’t do it, can you?
Sprinklers are intentionally designed to require 100% overlap of watered areas. That means each sprinkler throws water ALL the way to the next sprinkler in each direction. READ THAT AGAIN!
That’s right, 100% overlap of watered areas is REQUIRED or you will get dry spots! This is known in the industry as “head-to-head coverage or head-to-head spacing”. A lot of those free design guides you find in stores and on the Internet get this wrong. They don’t show enough overlap! The writers of those brochures think you are going to look at the overlap and buy the brand of sprinkler that shows the least sprinkler heads. So they try to make it look like you can use less sprinklers with their brand. After you’ve bought the sprinklers if you have dry spots, well hey, it’s YOUR problem now! You’ll probably just buy a few more of their sprinklers to get rid of the dry spots. In fact, it will probably take more sprinklers to fix the dry spots than it would have to do it right the first time. $$$ Ching, ching!
Rule: Sprinkler Radius = distance between sprinklers
One more time: The water from any single sprinkler should actually get the sprinklers on each side of it wet!
Now that I’ve told you that you SHOULD use head to head spacing I’m going to backtrack a bit and tell you that you can space a few of the sprinklers slightly farther apart as needed to work around odd shaped areas. I still recommend that you keep at least 80% of the sprinklers at head-to-head spacing! Take the sprinkler head watering DIAMETER and multiply it by 0.6 to get the absolute maximum distance that should ever occur between any two adjacent sprinklers. (Remember most manufacturer’s give you the radius of the sprinkler, you need to multiply by 2 to get the diameter.) For example, 15′ radius spray heads should never be more than 18′ apart (30′ diameter x 0.6 = 18′). Note that we rounded to the nearest foot. If the sprinkler system is in a windy area I suggest the majority of the sprinklers be spaced at 45% of the diameter (that’s closer than head to head!), as winds over 10 mph really mess up the sprinkler patterns.
(Optional reading for those who need explanations.) Back when I designed my first sprinkler system in High School I wondered why they wanted so much overlap of the sprinklers. It seemed to me to be nothing more than a ploy to sell more sprinkler heads! I was smarter than that, so I stretched them out to save my folks some money! The result was big dry spots, and my parents wound up replacing the sprinkler system a few years later. (They never said anything about it to me, I just noticed the new sprinklers a few years later on a visit home from college.) Ouch! Not a good start for a future irrigation expert! Now that I’m a bit wiser and more knowledgeable I realize there is a good reason behind the head-to-head coverage. Unfortunately, it’s rather hard to explain. The perfect sprinkler would put out a pattern of water that is heaviest right next to the sprinkler, then uniformly declines out to the radius. So the farther you move away from the sprinkler, the less water falls on any given patch of ground. When we test sprinklers for water coverage we set up a series of cups between the sprinklers to collect the water that falls. That way we can see how much water falls at various distances from the sprinkler. In the diagram below you can see what happens when there are various distances between the sprinklers.
In example “A” the sprinklers are just barely overlapping and much more water is falling in the cups next to the sprinkler heads. But the middle 3 cups are only getting ½ the water of the cups next to the sprinkler. If you watered long enough to keep the middle green, the areas around the sprinklers would turn to mud! In example “B” we see that moving the sprinklers closer together has evened up the amount of water a bit more. However the areas near the heads are still getting 25% more water than the other areas. Not enough to cause mud, but you would definitely see rings of greener grass around the sprinklers! Example “C” shows almost head-to-head spacing. The cups are almost all uniformly full! So don’t stretch the distance between sprinklers.
What if you need a smaller radius than the sprinklers available?
Almost all sprinklers have a radius adjustment device on them so that you can reduce the radius of the water throw. This is one way you can adjust for narrower areas. Keep in mind that for most sprinklers you can’t reduce the radius by more than 50% without causing problems. The other solution for smaller areas is to use nozzles made to spray less far, or that spray a special pattern. An example of a special pattern would be the nozzles that spray a 4′ x 30′ rectangular pattern. These are commonly used in long, narrow areas.
Remember if you reduce the radius of the sprinkler you must reduce the distance between sprinklers by the same distance! Keep the coverage head-to-head! Calculating the GPM for sprinklers when you reduce the radius is easy:
For spray heads you just use the manufacturer’s chart. When you use the radius adjustment on a spray you are simply reducing the water pressure by closing a small valve in the nozzle. As the pressure drops, so does the radius. Just look at the manufacturer’s chart for the radius you plan to reduce the sprinkler down to. Then read the GPM for that radius! For example, your designing for 30 PSI. The radius at 30 PSI of the sprinkler you selected is 15 feet with 1.85 GPM according to the manufacturer’s chart. But you want the radius to be 14 feet. Looking at the manufacturer’s chart you see that the radius of the same sprinkler is 14′ at 25 PSI with 1.65 GPM. So the GPM of that sprinkler if you reduce the radius to 14′ will be 1.65 GPM. That’s because when turn the radius adjustment screw to reduce the radius to 14′ what you REALLY did was reduce the pressure to 25 PSI!
For rotor heads the GPM stays the same no matter how much you reduce the radius! That’s because reducing the radius on a rotor doesn’t change the amount of water coming out of the nozzle. To change the radius a small screw extends into the stream of water coming out of the nozzle. The tip of the screw deflects the water which “screws it up” (pun intended) so it doesn’t go as far. This creates another problem, however, which is that it really messes up the uniformity of the water. So when you use the radius adjustment on rotors, you tend to get dry spots. This is one reason I strongly suggest that you use a smaller nozzle if possible rather than using the radius adjustment screw on the sprinkler. The other reason is that when you reduce the radius you really should also reduce the GPM of the sprinkler. Otherwise there will be a lot more water under the sprinkler with the reduced radius. Bottom line- use the radius adjustment screw on rotors only when nothing else will work.
Warning for rotors only:
When designing systems with rotors do NOT rely on the manufacturer’s stated radius for design. They get those distances by testing the rotors inside a building with no wind. The real world is harsher! If the gallonage of the rotor is less than 6 GPM the maximum spacing should never be more than 35′ between rotor type sprinklers.
Stryker’s Rule: the spacing in feet between rotors can never exceed the operating pressure in PSI at the sprinkler inlet (So a rotor with a 30 PSI operating pressure = 30 foot maximum spacing between rotors. Yes, I know the package says you can space them farther apart.)
Ignore the rule above and you will be very sorry!
Sprinkler Precipitation Rate and GPM
The precipitation rate is the amount of water the sprinkler throws onto the area it waters, measured in inches per hour. (Inches per hour is how deep, in inches, the water would be after one hour if it didn’t soak into the ground or run-off.) Precipitation rate must be considered when selecting your sprinkler heads to eliminate water application uniformity problems (dry spots).
Spray Heads: Almost all sprinkler manufacturers make their spray heads so that you can mix and match nozzle patterns and the precipitation rates will still match for all the heads. This is referred to as “matched precipitation rates”. Look for this feature when selecting your sprinklers. Important: do not mix different brands of spray heads and nozzles together on the same valve circuit without checking to see that they have the same performance specifications. Just because the nozzle will screw into the sprinkler body doesn’t mean it’s designed to work with that sprinkler!
Rotors: Rotor-type heads aren’t quite as easy. You must select the appropriate nozzle size for each rotor in order to match the precipitation rates. A simple illustration will help explain. Rotor heads move back and forth across the area to be watered. The rotation speed is the same regardless of whether the rotor is adjusted to water a 1/4 circle or a full circle. So the stream from a 1/4 circle head will pass over the same area 4 times in the same amount of time that it takes for a full circle head to make one pass over the area it waters. With the same size nozzle in both, a 1/4 circle rotor will put down 4 times as much water on the area under the pattern as a full circle rotor will. (Remember that after every quarter turn the 1/4 circle rotor reverses direction and covers the same area again!) To match the precipitation rates between these sprinklers, the quarter circle rotor must have a nozzle that puts out 1/4 the amount of water that the full circle nozzle puts out! A half circle rotor must have a nozzle that puts out 1/2 the water of a full circle. This is why when you buy a rotor-type sprinkler head they often include a handful of different size nozzles with it. Wait, there’s more (don’t panic yet, there is a simple solution forthcoming)!
If you have rotors that are adjusted for different radii you will need to adjust the nozzle size to compensate for the radius change also! For example if most of the rotors are set for a 30 foot radius, but one is adjusted down to 20 ft., the 20 ft. one will need a nozzle 1/2 the size. (Remember: when you reduce the RADIUS by 1/3 you reduce the AREA by a little more than half.)
Avoid using rotors with nozzle flows that are less than 2.5 GPM, except in corners (quarter circle patterns). Flows under 2.5 GPM give very poor coverage due to the tiny water stream. Even a slight breeze will distort the watering pattern and give you dry spots. I strongly suggest that you stick to using nozzles as close as possible to the GPM of those in the cheat chart below.
O.K. Now that you understand the principles, let’s simplify this a bit by using a cheat chart…
Unless you really know what you’re doing (in which case you wouldn’t be reading this tutorial), you should stick with the nozzles on this chart:
Quick & Dirty Guide for Rotor Nozzle Selection
1. Find the section of the chart with your desired spacing.
2. Find the pattern (1/2, full circle,etc.) of the sprinkler.
3. The chart tells you the GPM the nozzle must have.
4. Use a nozzle size that comes close to matching both the PSI – GPM combination.
5. Ignore the radius given by the manufacturer.
6. Be sure to read the notes below the chart!
For 20-29′ spacing between sprinklers- 1/4 circle . . . 30 PSI – 0.8 GPM
1/2 circle . . . 30 PSI – 1.6 GPM
3/4 circle . . . 30 PSI – 2.4 GPM
full circle . . 30 PSI at 3.2 GPM Important: see notes below!
For 30-39′ spacing between sprinklers- 1/4 circle . . . 40 PSI – 1.5 GPM
1/2 circle . . . 40 PSI – 3.0 GPM
3/4 circle . . . 40 PSI – 4.5 GPM
full circle . . 40 PSI – 6.0 GPM
For 40-55′ spacing between sprinklers- 1/4 circle . . .55 PSI – 3.0 GPM
1/2 circle . . . 55 PSI – 5.5 GPM
3/4 circle . . . 55 PSI – 8.0 GPM
full circle . . 55 PSI – 11.0 GPM
It is critical that the water pressure (PSI) at the sprinkler be as high, or higher, than the distance between the sprinklers in feet (per Stryker’s Rule). For example, if you space the sprinklers 45′ apart, you must have at least 45 PSI of pressure at the sprinkler inlet. That’s the pressure at the sprinkler inlet, not the total pressure available. Remember, you will lose pressure in the pipes and valves, so the pressure at the sprinkler inlet will be lower than your available pressure! Go back to the tutorial pressure loss pages to figure out how much pressure will be lost in your sprinkler system.
Select the nozzle size closest to these GPMs without regard to the radius the manufacturer gives. For example, if you are looking at a 25′ radius, the chart above says to use a 1.6 GPM nozzle for a half-circle rotor. But you happen to notice that the rotor manufacturer’s literature says that at 25 PSI, a 1.6 GPM nozzle has a radius of 32 feet. So why am I telling you to space it at 25′? When the manufacturer tested the rotor on their test range (inside a large building with no wind) they measured a few drops of water 32′ from the rotor. When you install it out in your yard it will not perform as well. You may still get a few drops of water 30′ or even 32′ from the head, but not enough to grow anything. You need to trust me on this one! Remember, if the sprinkler sprays too far, most rotors have a radius reduction screw that will allow you to very easily reduce the radius. But, if the rotor does not spray far enough there is nothing you can do about it without a major expense! Best to play it safe.
You may want to make additional adjustments to nozzle sizes after installation to compensate for your specific conditions. Most rotors now come with a “nozzle tree” that contains most of the different nozzles for the rotor, so you can change the nozzle sizes if you need to. Some manufacturer’s don’t offer nozzles sizes larger than 3.0 GPM for their economy-priced heads (providing those extra nozzles would probably cost them at least another nickel in costs!). You may need to upgrade to the next better model line if you have a large yard! The larger size nozzles for 40′ spacing are not available with most of the “mini-rotor” models sold for residential use. You will need to upgrade to the next model. Also, sometimes other nozzle sizes are available separately from the manufacturer, for example low angle nozzles. You will probably need to get these from a store that specializes in irrigation sales, rather than a hardware or home store. Look in the yellow pages under “Irrigation” or “Sprinklers”, or try one of the online stores listed in the tutorial links pages.
There is a conflict between the nozzles recommended for the 20-29′ spacing range of the chart and my previous advice to “avoid using rotors with nozzle flows that are less than 2.5 GPM”. This is because the Nozzle Selection Guide assumes you will be mixing 20-29′ radius rotors together on the same valve with 30′ plus radius rotors. To keep from having enormous nozzles on the larger radius rotors I am recommending that you use smaller nozzles than I would otherwise consider for the smaller radius rotors. This is essentially a compromise. Sometimes it is not practical to obtain perfection! If all or a majority of your rotors will be spaced at 20-29′ apart, then you should probably use larger nozzles than I recommend in the chart. In other words, use those listed in the chart for 30-39′ spacing for the 20-29′ spacing. This will help avoid problems caused by the wind blowing the spray out of the irrigated area. However, if your sprinkler system will be located in an area with little or no wind you can go ahead and use the smaller nozzles in the chart. What is little or no wind? Go outside in the evening or early morning when you will likely be irrigating. If you can feel the wind blowing even gently against your face, I would consider that enough wind to need the larger nozzles.
If you calculate the precipitation rates you will notice that the shorter spacings result in a higher precipitation rate than the larger spacings. This is because the smaller heads with lower GPM rates are more susceptible to wind and evaporation, and thus it is assumed less of the water is actually reaching the ground. The higher precipitation rate compensates for this.
If you are designing a sprinkler system for an area where the wind blows a lot you should look at the Irrigation and Wind FAQ.
Select Your Sprinklers
If you haven’t started shopping for sprinklers yet, now’s the time to start checking out what’s available. Check out which sprinklers are available and look them over. Write down a list of the heads you think will work well for your irrigation system on your Design Data Form. Be sure to list the PSI and GPM for each head as given in the manufacturer’s literature, along with the maximum spacing between heads.
One last warning!!!
Do not blow-off my advice on sprinkler spacing in order to save a few bucks on sprinkler heads! Right now you may be feeling pretty smug about how much money you saved by stretching the sprinkler spacing. But next summer you’re going to look pretty stupid to the neighbors, standing out there with a hose watering the yellow spots your new sprinklers don’t cover! I have a collection of “wish I’d listened to you” letters from people who didn’t take this advice. I get a few more of these every year, and these are just the brave folks willing to confess they messed up. They all say you should listen to me on this!
Later on you will need to know the flow rate for each sprinkler you use, so it might be helpful to make some notes on the back of your Design Data Form showing the nozzle size and GPM you will need for each different sprinkler you plan to use. Otherwise you’ll wind up having to look the information up over, and over, and over…
Draw the Sprinkler Heads on Your Plan
You’re now ready to pencil in the sprinkler head locations on your drawing. Hallelujah! I know it seems like it took a long time to get here, but to do a good job we needed to cover a lot of background information! Use a pencil to draw in the sprinkler heads so you can easily make adjustments to the locations later. Many people find it helpful to use a compass to draw a light pencil line showing the radius of water throw for each head.
Remember these tips:
Keep the distance as uniform as possible between heads. To the extent possible a sprinkler should be equal distance from the adjacent sprinkler in each direction (forming a triangle if possible). Changes in spacing between adjacent sprinklers should be made as a gradual transition when possible.
Try to position heads so that if you were to draw a straight line between adjacent heads they would form an equilateral triangle (each side of triangle is same length). This is called “triangular spacing” and creates more even water coverage than “square spacing” (ie; lines between 4 heads form a square). That said, you will often be unable to form a triangle so don’t panic if you can’t.
Don’t stretch the spacings, use “head to head” spacing. Using too many sprinkler heads is seldom a problem, using too few sprinklers heads is ALWAYS a disaster!
Start by drawing a sprinkler in each corner. Next, draw sprinklers around the perimeter of the irrigated area, watching that they are not too far apart (one more time, better too many than too few!). Adjust the locations to make the spacing between sprinklers as even as possible. After the perimeters are done, then draw the sprinklers in the interior area.
If the sprinklers need to overlap so that the spray from one head goes over and beyond the next that’s OK. While you don’t want to over-water, it is always easier to correct an over watered area than a under watered one. For example, you can use the radius adjustments on the sprinklers to cut down the water in the over-irrigated areas. If need be you can even remove or relocate a sprinkler later. It’s much easier to remove one than to add one!
Sprinklers that are placed closer than 6 feet apart need some special consideration. Standard spray-type sprinklers don’t work well if the radius is adjusted below 6 feet. (The opening the water goes through is so tiny that the normal expansion of the plastic or metal on a warm evening can close off the water flow!) If the area is long and narrow (4′ wide or less), use the strip pattern nozzles. I prefer the so called “side-strip” type that you place along the edge of the area, they have better patterns than the center strip nozzles. End-strip nozzles have notoriously bad patterns, they shouldn’t be more than 10′ from the next head! When using standard spray sprinklers (like quarter, half, and full circles) in areas where the radius must be adjusted to less than 6 feet use a “pressure compensating device” to reduce the radius. The pressure compensating device is normally installed under the nozzle where it reduces the flow and pressure through the nozzle. The good news is that by using a under sized pressure compensating device you can also reduce the nozzle radius! Unlike the adjustment screw on the nozzle these devices work well regardless of the temperature. However, you will need to select the proper size pressure compensating device for each nozzle. It is possible that every nozzle will need a different size! To select the right device you use a special chart provided by the pressure compensating device’s manufacturer. The chart will tell you exactly which device you must use with each different nozzle in order to get the radius you want. Most major sprinkler manufacturer’s make pressure compensating devices for their spray sprinklers, and the charts you need can be found in their catalogs. You may need to go to a commercial sprinkler supplier to find them.
Study the example drawing below.
Again, notice that the radius of each sprinkler’s spray goes all the way to the next sprinkler! This is critical.
Note that in the example above only the lawn area outlined with a green curving edge is being watered. The area between the lawn (green line) and the edge of the property (brown line) would most likely be planted with shrubs and irrigated separately from the lawn. In most cases a drip system would be considered for watering the shrubs as it is less expensive and more efficient. See the separate guidelines for designing drip irrigation systems.
Bonus landscape design tip: Creating a border of shrubs around the perimeter of your yard is, in most cases, a good landscape design practice. A shrub border helps to reduce the visual impact of the fence (assuming that like most residential properties you have a fence.) Shrubs also typically use less than half the water of lawn areas of the same size, saving money spent for water. Once a month you need to weed and trim shrub areas, as opposed to the lawn that needs to be mowed every other week at the least in summer. A border using shrubs of various sizes, textures and colors can add greatly to the attractiveness of your yard. Place smaller shrubs near the lawn, with larger growing varieties behind them next to the fence.
Sprinkler Layout for Narrow Planters:
This example shows the typical placement for sprinkler heads in a narrow planter. In this example, special spray sprinkler nozzles called “end-strips” and “side-strips” are used. These nozzles spray a long, but narrow, pattern. A typical pattern is 4′ x 30′ (4′ out and 15′ in either direction from the head). There are also spray nozzles called “center-strips” which don’t work as well. Be careful when using end-strips. They tend to have a weak coverage area on either side of the nozzle (the yellow area in the drawing above). Avoid using 2 end-strips facing each other in a lawn area. If possible always install a side-strip in the middle between 2 end-strips. The sprinkler layout above is for lawn. In a shrub area you can eliminate the sprinklers on one side as long as the width of the planter is 4 feet or less- so you can install the sprinklers on one side only. Shrubs don’t need as even a watering pattern. Lawns require heads on both sides. Note the triangular arrangement of the sprinklers, which gives more even coverage. Yes, it takes an extra head to create the triangle pattern, and you need to space the heads a little closer together than the normal maximum on one side to create the “triangle pattern”, but it’s worth the cost.
For narrow strips wider than 5′ you would use regular half circle heads on both sides. The distance between the sprinkler heads should not be more than 1 foot greater than the width of the planter. In other words, if the planter is 8 feet wide you would install half circle heads on both sides of the planter, not more than 9 feet apart from each other. As with the example above, it is best if you arrange the sprinklers in a triangular pattern.
As we saw previously, the flow rate in gallons per minute (GPM) of each sprinkler head is determined by the nozzle installed in the head. It is necessary to know the GPM for each head in order to determine which heads will be connected to each valve and in order to determine the size of each pipe in the sprinkler system.
You will probably need to dig up the sprinkler manufacturer’s literature again. In the literature the manufacturer shows different GPM and radius information for each sprinkler nozzle based on the operating pressure (PSI). Now we can use that information to find the GPM for each sprinkler head. First, determine what the SPACING is between each head and the others around it. Next, look for the radius closest to that spacing and use the corresponding GPM as the flow for the head.
Write down on your plan the GPM for each sprinkler next to the sprinkler symbol.
Hint: You will find the GPM and radius data for many of the popular sprinklers in the product reviews .
Example: You note that a spray type head on your plan is a 1/2 circle pattern and the distance to the 3 closest adjacent heads are 13 feet, 12 ft., and 14 ft.. So the spacing for this head is 14 ft. (the highest of the 3). Looking at the manufacturer’s literature you note that a radius of 14 ft. for the 1/2 circle nozzle in this sprinkler requires a pressure of 25 PSI and a flow of 1.65 GPM. Write down the flow of 1.65 GPM next to the sprinkler head on your drawing. You then repeat this procedure for each sprinkler head on your drawing.
The next step in designing your irrigation system is to identify the individual hydro-zones that exist in the area to be irrigated. Different areas of your yard have different water needs. Each of these areas is called a “hydro-zone”. You need to irrigate them separately from one another to keep from drowning some plants while others are dying of thirst. For example, a grass lawn will almost always need more water than a shrub bed. Plants in the shade of a house need less water than those in direct sun. Tropical plants need more water than desert plants. Remember that over-watering plants can be as harmful to them as underwatering. Many plant diseases are the direct result of over-watering, particularly fungus and molds.
Using a pencil lightly outline the different hydro-zones in your yard on your plan. Some hints:
Lawns and shrubs should NEVER be in the same hydro-zone, so start by creating two hydro-zones, lawns and shrubs.
Shady and sunny areas should not be in the same hydro-zone. The shadiest areas are typically in the shadow of buildings where little or no direct sunlight reaches all day long. Go out and walk around your yard. Look for places where the soil stays moist when compared with the rest of the yard. Separate the sunny and shady areas of the lawn area into different hydro-zones. Do the same for the shrubs areas.
Plants with different water requirements should not be in the same hydrozone. Show a separate hydro-zone for any grouping of plants that need more or less water than the others. If you’re not familiar with the water needs of various shrubs look them up in a good garden encyclopedia. You can also tell a lot just by observation. Do some plants in your yard seem to wilt easier than others? On large projects you may also have different soil types in various parts of the irrigated area. These may also need separate hydro-zones. This is very common for golf courses and parks.
Never combine spray heads, rotors, or drip irrigation in the same hydro-zone. The water application rates are different for each of these, which will cause either dry or wet spots. For example, rotors often apply water at half the rate as spray heads. So if you were to combine spray heads and rotors on the same valve, and then turned on the water long enough to apply just the right amount of water in the spray head area, the area with rotors will only get half the water it needs.
The irrigation for each of these hydro-zones will need to be controlled by its own valve. This way the watering times can be individually adjusted for the specific needs of each hydro-zone. Nothing gets over or under watered. Over and under-watering is a major factor in promoting plant disease, and it wastes water. In some small yards it may not be practical to create separate hydro-zones for all the different water needs. This is an individual decision that you will need to make. Another option is to relocate or replace plants that don’t fit in well with others in the area. I often adjust the outlines of lawn areas to avoid small areas I know will have a different hydro-zone than the rest of the lawn, such as in the shade of a building, or under a large tree.
Drip Irrigation Systems:
If you use drip irrigation for your shrubs you can much more easily mix plants with varying water uses together. The best way to do this is to install two separate drip systems in the same area, one irrigating just the high water users and one just the low water users. Another cheaper, but less effective, way is to install more emitters at the plants which need more water. The disadvantage of this second method is that most water loving plants don’t just want more water, they want it more frequently, which is not possible when everything is on the same system. Irrigating too frequently is a major cause of plant disease so be warned!
Previously you wrote down your “design flow” on your Design Data Form. As you remember that was the maximum amount of water available for the irrigation system measured in gallons per minute (GPM). Hopefully you also noted on your plan the flow (GPM) for each sprinkler head. Now you need to divide the irrigation system into valve zones that do not exceed that amount of water. Remember that the valve zones can’t cross over the boundaries of the hydro-zones you drew previously. (Hydro-zones can’t overlap valve zones.) Here’s an easy way to do this:
Add together the GPM for all the sprinklers in a hydro-zone.
If the total GPM of all the sprinklers in the hydro-zone exceeds the design flow GPM, you will need to divide the hydro-zone into more than one valve zone.
The total GPM for each valve zone should never exceed the design flow GPM.
Drip irrigation and sprinkler irrigation may NOT be mixed together in a single valve zone. Fixed spray type sprinklers may NOT be mixed with rotor type sprinklers in the same valve zone. You need to create separate valve zones for each of these.
Repeat this procedure for each hydro-zone.
Lightly circle on your plan the heads that are in each valve zone as shown below.
Now identify the location where your valves will be installed. If the valves will be above ground pick somewhere they will be hidden, like behind shrubs. Usually they are placed near the water source but there is no reason they need to be. Remember that if you plan to use anti-siphon type valves they must be installed at an elevation 6″ HIGHER than the highest sprinkler head, so they will probably need to be on the uphill side of the irrigated area. The valves do not need to be grouped together in the same location, you can place them where most convenient. Placing the valves in small groups of 2 or more, close to the areas they will water, can often save money by reducing the amount of pipe needed.
Draw in a valve symbol on your drawing for each valve zone. This will represent the valve that turns on and off the sprinklers in that valve zone. See the illustration on the next page of the tutorial for a typical valve symbol.
Sprinkler Pipe Layout
Now that you have the valve zones shown on your drawing it’s easy to add the pipes going to the sprinklers. Start with one of the valves and draw a line to the closest sprinkler in the corresponding valve zone. Then draw a line to the next sprinkler in the valve zone, and the next, etc. Some helpful tips:
For small residential sprinkler systems try using a different color pencil for the pipes in each valve zone. This will make your plan easier to understand.
Where possible you can minimize the amount of trenching by placing pipes together in the same trench. Show these pipes side-by-side on your plan.
Run the pipes as efficiently as possible. In most cases this will be the shortest possible route between each sprinkler, but this is where you need to just look at your plan and think about it a bit. You may find it easier to run one pipe down the center of an area and spur off of it to each sprinkler. Or it may be easier to split the piping with one pipe going to half the sprinklers and the other going to the other half. Some may want to minimize the number of trenches, even if it means using a less direct route for the pipe so two pipes can share a trench. There is no set routing pattern that you must use for the pipe. If for some odd reason you need to route the pipe all the way around the yard to get to a sprinkler only a few feet away from where you started that’s O.K. Try several different layouts until you find one that YOU like, that fits YOUR needs.
Show no more than 2 pipes connecting to a sprinkler head– one coming into the sprinkler, and one going out. If you need to branch off from the sprinkler with a 3rd pipe, show the 3rd pipe branching off of the 1st pipe just before it goes into the sprinkler. There is no part made that will allow 3 pipes to connect together at a sprinkler head location. Study the sample drawing below for examples.
Try to avoid running pipes within 5 or 6 feet of existing trees. The roots will make it hard to dig trenches for the pipe. With really big trees I try to keep the trenches out from under the canopy of the tree. If I need a sprinkler in that area I run the pipe around the perimeter then go straight in toward the trunk to the sprinkler head. Of course, this may not always be possible. Sometimes you will just have to go through an area with tree roots.
Splitting flows or splitting hairs? You may have heard that the flow from each valve should always be split just after the valve, with one pipe going to half the sprinklers and the other pipe going to the other half. The reasoning is that this “balances” the system. Good designers can balance the flows without resorting to this old method. You are well on your way to becoming a good irrigation designer, so you can forget about such amateurish methods! Route the pipe however you want to route it!
Draw the lateral pipes between the sprinklers and the valves. If you haven’t drawn the mainline pipe from the valves to the water source, draw it now also.
Determine Flows in Pipes:
In order to determine the pipe size we need to know the flow rate (GPM) of the water in the pipe. Calculating the water flow in each section of pipe is extremely easy, but many people have problems with it. They try to make it too complicated. Just observe the layout of the sprinklers and ask yourself which sprinklers are DOWNSTREAM of this pipe section. It’s simple logic, the water must flow through this pipe to reach the sprinklers downstream. Add the total GPM of those sprinklers together and you have the GPM that will be flowing through the pipe.
Start at the valve. The first section of pipe goes from the valve to the first sprinkler head. All the water for every sprinkler operated by this valve must flow through this section of pipe to get from the valve to the sprinklers, right? So the flow in GPM for this section of pipe is the total of the GPM of all the sprinklers operated by the valve added together.
The remaining sections are just as easy. The total flow through each section of pipe is the same as the total GPM of all the sprinklers downstream from that pipe section. Add together the individual GPMs for each of those sprinklers to get the flow through the pipe section. Don’t make it harder than it is! If you have a short spur pipe leading off to a single head, then only the water going to that head will pass through the spur pipe! So the flow for the spur pipe is the same as the GPM of that single head. Carefully study the sample design below.
Using a pencil, write the flow for each pipe section down on your drawing next to the pipe.
Well, if you are working through the Sprinkler Design Tutorial, you’re now pretty much finished with your irrigation design. Here’s a few reminders and additional items to consider.
Automatic controllers: For automatic systems you will need a controller (often called a “timer”) with one “station” for each valve. If you have both lawn and shrub areas you should make sure the controller has 2 or more “programs”. Multiple programs are somewhat like having several “timers” in the same controller. This allows you the flexibility to run the lawn and shrub irrigation on different days. Study the different models and features available on various controllers. They range from simple timers to extremely complex computerized units that can monitor all the functions of your entire home! I suggest you take a look at the article on Smart Controllers if you are interested in the latest innovation for saving you time and water.
Isolation valves: It’s a good idea to install a manual shut-off valve at the point where your irrigation system connects to the water supply. I know I already covered this, but not doing it is a big regret that I hear often. An isolation valve allows you to shut down the irrigation for control valve repairs without shutting off the water to your house. You will have to repair a control valve at some time. I recommend using a “ball valve” for the isolation valve, as ball valves are the most reliable and reasonably priced shut off valves. Most inexpensive “Gate valves” will leak.
Wires for valves: For wires going to the automatic valves use wire made specially to be buried. Most people use a special direct burial cable made for irrigation systems. The cable contains 3, or more, separate, 18 gauge wires. On commercial systems the standard wire used is “#14-1 AWG-UF” which is a single strand, direct burial type wire. One white color “common” wire goes from the controller to every valve, and one individual “lead” wire of a color other than white goes to each valve from the controller. Be sure to read the Irrigation Installation Tutorial. Also there is a sketch of typical irrigation system wiring that should help you understand the wiring.
Details: To further help you there is a collection of installation details. These simple sketches will help you figure out how to assemble your irrigation system. These installation detail drawings are normally included as a part of the design drawings for an irrigation system.
Filters: I recommend you install a screen-type water filter upstream of the valves. Drip systems should always have a filter! This helps reduce maintenance problems caused by small bits of sand which are found in almost all water systems. These small sand grains can make the automatic valves malfunction and also clog sprinkler heads over time. A $50.00 filter may seem expensive, but it is a lot cheaper than a $100 valve repair job or replacing a dead lawn. I recommend a “150 mesh screen” in the filter. The filter can be installed underground in a box if you don’t want it visually cluttering up your landscape. On the other hand, it is nice to have it in a more convenient above-ground location for maintenance. Remember, you need to clean the filter screens at least once a year if not more often! For tons more information on filtration see the Irrigation Water Filtration Tutorial.
Cold Winter Precautions: Unless your irrigation system is in an area where it never freezes you should insulate the backflow preventer and any other above ground equipment. Backflow preventers are very expensive, you don’t want an unexpected freeze to catch you off-guard. A few years back that happened here in California and thousands of backflow preventers had to be replaced because the water froze in them and they split open! I usually use foam insulation tape to wrap the backflow preventers and above ground valves, then wrap the insulation with a layer or two of 10mil black plastic tape to protect it. There are also some pretty neat backflow preventer blankets (essentially a big insulated bag), that are made to fit over the backflow preventer like a big coat. They work good, I use them. (I have a small one in my truck that I use to keep cans of soda cool when I’m on the road. It also makes a great pillow!) If the backflow preventer has air vents or a water blow-off outlet it is extremely important that they not be blocked by insulation! There should be instructions that come with your backflow preventer.
Winterization: In areas where freezing weather occurs you need to take precautions to protect your irrigation system from freezing. There is a whole tutorial on winterizing your sprinkler system in areas where it really freezes hard. It covers the various methods used, advantages and disadvantages of each, and what you will need to install as part of your new sprinkler system for each method.
That’s hard to say. I priced out the materials for the little sample irrigation system at the top of this page at $375.00. That included reasonably good quality sprinkler heads, “funny pipe” type risers, Cl 200 PVC pipe, anti-siphon valves, and a very inexpensive $50.00 controller. That comes to about $0.25 per square foot of irrigated area. You may need to add extra for a better backflow preventer and better controller. I would suggest in most cases that you estimate at $0.25 per square foot plus the controller and backflow preventer cost.
Installation generally costs about 1.5 times the cost of the materials. Installation costs can vary wildly, be sure to get 3 bids. If any bid is significantly lower than the others I would be extremely suspicious and use extreme caution before hiring that cheap contractor. Never pay a deposit up front unless you are willing to risk losing that money. If the contractor needs up front money insist that he deliver materials equal to the deposit value to your house prior to payment. Remember if the contractor needs money up front to buy supplies that means the suppliers won’t sell to him on credit. Suppliers sell to almost everyone on 30-day interest free credit, so if they don’t trust him/her to pay them that should be a huge warning to you! The irrigation installation business is very easy and cheap to get started in, and as a result it has a huge number of contractors are under-financed, then under-bid to get work, can’t complete the work, and fail. Understand that property laws in the USA allow the supplier to place a lien on your home for the value of any materials the contractor buys for your sprinkler system, but does not pay for. It does not matter if you paid the contractor already for those materials. The supplier can still make you pay for them again. That is the law. Be smart, protect yourself!!!
Now you’ll probably want to move on to the tutorial on to the Sprinkler System Installation Tutorial. It covers in more detail the various irrigation parts you will use, like sprinkler risers. It also teaches you to “talk sprinklers” (so you can sound like you know more than you do!), helps you make a list of the materials you will need to buy, provides some helpful forms you can print out, explains which tools can make your day or break your back, and a few other tips and tricks! Be sure you read it before you buy anything or start digging!!! (Just when you thought you were finished!)
End of Tutorial
(As you will note, I’ve enlisted some assistance from my family members!)
Written by Jess Stryker, Landscape Architect, unless noted otherwise
Well, if you have been reading my tutorials, I guess it’s pretty obvious that I’m not recommending you use 1/2″ pipe. I have a number of reasons for this.
1/2″ PVC pipe is generally not available in most areas except in SCH 40 type.
The water capacity of 1/2″ pipe or tube is very low.
1/2″ PVC pipe is hard to glue together without using too much glue. The glue piles up on the inside of the pipe when you insert it into the fitting and blocks the water flow. Too much glue also weakens the wall of the pipe and a leak develops after a few years.
Using 1/2″ pipe means you have to have another size of spare pipe and fittings on hand for repairs.
But the biggest reason is that 1/2″ pipe leaves no flexibility for future changes or additions to your sprinkler system. If you ever need to add another sprinkler to the pipe you’re screwed.
My conclusion: The small amount of money saved by using 1/2″ pipe just isn’t worth the hassle and risk.
As water moves through a pipe it loses pressure due to a phenomenon commonly called “friction loss”. Much of this loss is caused by turbulence, but we call it friction loss for simplicity. The amount of friction loss is determined by the type of pipe, the diameter of the pipe, the amount of water flowing through the pipe, and the length of the pipe. A complex formula (called the Williams/Hazen Formula) predicts the amount of pressure that will be lost due to friction loss. The water also loses pressure each time it passes through a valve, a backflow preventer, or anything else it encounters on it’s way to the sprinkler head. Even a bend in the pipe causes pressure loss! Don’t panic over the formula, we’ll use a pipe sizing chart or a friction loss calculator!
You need lots of pressure at those sprinkler heads!
The sprinkler head needs a minimum amount of water pressure to work properly. The manufacturer’s performance charts tell you how much pressure is required to achieve a specific radius for the water. As the pressure increases so does the flow (GPM) and the radius of the throw. So in order to assure that there is enough pressure to make the sprinklers operate as they should, we need to calculate the pressure losses between the water source and the sprinkler head. If the pressure loss is found to be too great, then we must reduce. The easiest way to do that is to use a larger size pipe.
DETERMINING THE SPRINKLER PIPE SIZE
There are several methods used to determine pipe sizes of sprinkler system lateral pipes. I’m going to explain two methods. One method is faster but less accurate, the other is very accurate but takes more time.
Pros: The fastest and easiest method. Requires a single, simple calculation and uses a chart to determine the sizes.
Cons: The learning curve to use it is a bit more difficult to understand. It uses an averaging system to arrive at pipe sizes.
See step-by-step tutorial for the Chart Method
Trial & Error:
Pros: Very accurate, calculates the pressure loss in each pipe section using a spreadsheet. Easier to understand.
Cons: Time consuming, need to enter data into the spreadsheet, uses trial and error to establish pipe sizes.
See step-by-step tutorial for the Trial & Error method
Which method should you use? For a beginner with a small irrigation system probably the Trial & Error system will be easier. Below are overviews of each method for experienced designers to use. Unless you are experienced you should probably read the full tutorial for the method you select.
Overview: CHART METHOD FOR LATERAL IRRIGATION PIPE SIZING
( ____ PSI x 100) / ____ Feet Total Length = PSI/100
____ PSI. Insert the maximum PSI loss for the valve circuit laterals into the formula where it says “____PSI.”
____ Feet. Insert the distance from the valve to the farthest sprinkler on the valve circuit in the space labeled “____ Feet Total Length” in the formula.
Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure.
The Pipe Size Table or Chart:
Sprinkler Pipe Sizing Chart for Laterals
PSI/100 = Desired PSI Loss in Lateral x 100 / Total length of Lateral
Flows shown red are over 5 feet/second. Use caution!
Find your PSI/100 value in the top blue row.
Read down the column to the value equal to, or higher than, the GPM in the pipe section.
Read across to the pipe size for that section in the right column.
Repeat steps 2 & 3 for next pipe section.
This table uses an averaging formula based on the assumption that all flows for any given size of pipe will not be at the maximum GPM for that size of pipe. In rare cases the PSI loss for the entire lateral may exceed the desired loss by up to 10%. This table assumes the use of Cl 200 PVC pipe, adjustments to the pipe sizes are required for other pipe types, such as poly or SCH 40 PVC.
Pipe Sizing Chart, Copyright 1979, Jess Stryker, All rights reserved.
Notes about the Pipe Sizing Chart:
Warning: The sprinkler pipe sizing chart is based on using Cl 200 PVC pipe. It also works for Class 125 (not recommended) and Class 160 (hard to find).
Schedule 40 PVC: If you plan to use Schedule 40 PVC pipe (“SCH 40”) for the laterals you need to make an adjustment before using the chart. Reduce the PSI/100 value you just calculated for the valve circuits to 1/2 the original values.
Polyethylene, Polybutylene: After you obtain your pipe size from the chart you need to increase it by one size to get the proper size for poly pipe. In other words, if the chart says ¾” PVC pipe, then you should use 1″ poly pipe. 1″ would become 1¼”, 1¼” becomes 1½”, 1½” becomes 2″, etc.
Go to the next line down and repeat steps 4-7 for the next pipe section.
The spreadsheet calculator will tell you the velocity and PSI Loss for each pipe section.
At the bottom of the calculator it will tell you the pressure loss total of all sections combined.
Change the pipe size if the velocity or total pressure loss is too high.
You must calculate the pressure loss for each of the possible water paths in the valve circuit.
Here is an example of the possible water paths for a valve circuit, shown in red, blue, and magenta.
Start with the water route that is the longest. In this case that would be the red route. There are 9 pipe sections in this route labeled 1-9. Enter the data from this route into the calculator. Use a larger pipe size if the velocity is not safe. Check that the friction loss “Total of All Sections” does not exceed your maximum allowable amount.
Write the pipe size for each section on your plan.
Now repeat the process for the blue water route and then the magenta color route.
It will not harm anything to use a larger pipe size. Period. If you are uncertain whether to use a 3/4″ or 1″ pipe, then you should use the 1″. Using a larger size pipe is ALWAYS the safest choice.
No, I don’t own stock in an irrigation pipe manufacturer and I’m not getting kickbacks for pushing bigger pipe! Unlike clothing, pipe can never be “too large”. Contrary to what might appear to be true, forcing water into a smaller pipe REDUCES the water pressure, and hurts sprinkler performance. This is because the smaller pipe creates more pressure loss due to friction and turbulence as the water flows through it. It’s another of those hard to grasp hydraulic principles! Just remember that when it comes to pipe, bigger is better! I’m always amazed at how many irrigation equipment sales people don’t know this most basic of irrigation rules. I’ve had clients tell me they were told to use a smaller pipe to keep the pressure up by tech support people at some of the major sprinkler manufacturer’s. That’s an industry disgrace!
So one more time to drill it into your head– You don’t decrease the pipe size to keep the pressure up- or down for that matter. That is totally, completely, wrong. The reason we use smaller pipe is to save money. Which of course, is a good reason! For those who want more specifics on this, there is a very boring scientific explanation at the bottom of this page.
Is it Pipe or Tube? For the most part I use the term “pipe” rather than “tube” on this page and elsewhere. Bad habit of mine (note that by reading carefully, you have found one of my faults!) The difference is the material they are made from. Steel and PVC plastic are generally called pipe. Polyethylene, PEX, and copper are usually referred to as tube. I often screw up and call tube pipe! 🙂
TRIAL & ERROR METHOD TO DETERMINE LATERAL PIPE SIZE USING A SPREADSHEET
This method involves trying various pipe sizes until a good combination is found.
Definitions you need to know:
Lateral pipe: all the pipes between the control valve and the sprinkler heads.
Mainline: The pipe that goes from the water source to the control valves.
Control Valve: The valve that turns on and off a group of sprinklers. Most often it is an electric valve operated by a timer.
Valve circuit: a single valve, and all the pipe, fittings and sprinkler heads downstream from it. In other words, all the sprinkler heads that start working when you turn on the valve are part of the same valve circuit.
GPM: Gallons per minute, a measure of water flow rate. Use primarily in the United States.
PSI: Pounds per square inch, a measure of water pressure. Use primarily in the United States.
You will need a spreadsheet Friction Loss Calculator.
Here’s a page with calculators for almost every type of pipe: Friction Loss Calculator Spreadsheets
Grab the appropriate spreadsheet for the type pipe you plan to use.
Now you just enter the appropriate data for each section of pipe into the calculator and then read the total pressure loss at the bottom of the spreadsheet. If the pressure loss is too high, then try making one of the lengths of pipe larger. The calculator will also give you the water velocity in each section of pipe, and warn you if the velocity is too high.
The best way to teach this is probably to walk you through a couple of examples.
If I may make a suggestion, download the spreadsheet for Cl200 PVC now, and open it up in a separate window. Then think about each step, enter the values I show into the spreadsheet, and actually try to duplicate what I do in the examples below. Something about actually doing this helps engage people’s brains. People tell me they read it twice and still don’t get it when they just read it, but as soon as they actually TRY it, then it suddenly makes sense. It’s called learning by doing, and it is considered the best teaching method. This process is simple, HOWEVER, it is not obvious and sounds illogical to those not trained in hydraulics.
A Simple Example:
The sketch above is an example of a very simple valve circuit with 5 sprinkler heads. In this example the sprinklers are 15′ apart and each sprinkler uses 3.7 GPM of water. The red numbers on the sketch are the total water flow for each pipe section in GPM.
Let’s assume we want to use Cl200 PVC pipe and we want a maximum total of 4 PSI of pressure loss in our lateral pipes.
If you are working through the Sprinkler Design Tutorial the maximum total pressure loss is entered on your Design Data Form in the Pressure Loss Table section. There you will see a figure you entered called “_____ PSI – Laterals”. That is the maximum PSI loss for the laterals, use that number here. If in doubt, 3 PSI is a reasonably safe value for most sprinkler systems.
If you don’t understand how to calculate the water flow in each section (the red numbers) you should take a look at the Sprinkler Pipe Layout page.
Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure. Example: 20 PSI sprinkler operating pressure. 20 x 0.20 = 4 PSI maximum pressure loss in circuit laterals.
If you don’t understand pressure losses in irrigation, see Pressure Loss & Selecting Your Sprinkler Equipment.
For advice on types of pipe (Cl200, poly, etc.) see Irrigation System Lateral Pipes.
To use the spreadsheet friction loss calculator to determine the pressure loss:
Download and open the Friction Loss Calculator.
There is a line on the spreadsheet for each section of pipe. So for this example you will enter data for 5 pipe sections.
Start with the pipe section closest to the valve as section #1, and work out to the farthest sprinkler head.
Start by selecting 3/4″ pipe for the pipe or tube size for all the sections. (See “why not 1/2″?”)
Enter the GPM for the section of pipe.
Enter the length of the section of pipe.
Use an error factor of 1.1
Go to the next line down and repeat steps 4-7 for the next pipe section.
The spreadsheet calculator will tell you the velocity and PSI Loss for each pipe section.
At the bottom of the calculator it will tell you the pressure loss total of all sections combined.
Here’s what the spreadsheet calculator looks like after we enter the data requested for each of the pipe sections using the example in the sketch above.
Note that the “Total of all Sections” shown at the bottom exceeds the 4 PSI maximum limit we set for pressure loss. Also notice that the velocity in two of the sections (highlighted in red) exceeds the safe level. The marginally high velocity highlighted in yellow is considered acceptable by most experts, since these are lateral pipes. (The marginal velocity level would not be as acceptable in mainlines.) Start by fixing the velocity problems. To decrease the velocity in those sections we will need to increase the pipe size. So let’s increase the pipe size for the two sections highlighted with red to 1″. Here’s what it looks like after the change:
Now the velocities are all within acceptable levels. Also note that increasing the pipe sizes reduced the pressure loss “Total of All Sections” shown at the bottom to 2.9 PSI, which is well below our maximum level of 4 PSI. That’s good, no more changes are needed. It is not possible for the pressure loss to be “too low.” As long as it is under the maximum it is fantastic. So what would happen if the pressure loss was still too high? If there was still too much pressure loss we would need to try increasing the size of some of the pipes to lower the friction loss.
So we now have pipe sizes that will work for each section of pipe in our lateral. I’m often asked at this point if it would be OK to make some of the pipes 1/2″ since the pressure loss is so low? The answer is yes, but you might not want to do it. See my explanation of the problems associated with the use of 1/2″ pipe.
A More Complex Example:
Now lets look at a more complex valve circuit. (Please note that this circuit is much larger than that found on a typical residential irrigation system. It would require much more water than most residences have available and is just used to show you an example of a much more complex layout.) As with the previous example we will assume that our maximum pressure loss value for the valve circuit is 4 PSI.
This valve circuit involves numerous paths the water may take. This makes the calculation a bit more complex, as a separate calculation is needed for each possible route that the water might take through the laterals on it’s way to the last sprinkler at the end of a pipe. If you look at the example above you will notice there are 3 sprinklers that are at the end of pipes, each sprinkler at the end of a pipe represents a different route the water can take. So this circuit has 3 and will therefore require 3 separate pressure loss calculations. The next drawing shows the possible water routes in magenta, blue, and red colors.
It may help to think of each path as the shortest route that a single drop of water could take to go from the valve to the last sprinkler on a pipe branch. For some people it helps to think of it as a road map and your looking for the shortest route to each of the dead ends at the end of the roads.
Start your calculations with the water route that is the longest. In this case that would be the route highlighted in red. There are 9 pipe sections in this route, I have labeled them 1-9 for clarity. Just as before, enter the data from this route into the calculator, and make all the pipe 3/4″ size. Here’s what the spreadsheet looks like:
As you can see there are a number of pipe sections highlighted red due to unsafe velocity. Change those pipe sections to larger pipe sizes until all the velocities are within safe levels.
Here’s the resulting spreadsheet calculator with the smallest possible pipe sizes. However, notice the Total of All Sections is 4.4 PSI, which is more than our 4 PSI maximum:
So we need to make some of the pipe sections larger in order to reduce the pressure loss (or friction loss.) Start by increasing the size of one of the the smaller pipe sections. Changing a 3/4″ pipe to a 1″ size is a lot less expensive than changing a 1″ pipe to 1 1/4″. So for the example lets change section 7 from 3/4″ to 1″. Doing that drops the Total of all Sections value to 3.77 in our example, below the 4 PSI maximum we set earlier. So now everything is good, these sizes will work for the “red” highlighted water route.
Now we add the pipe sizes from the spreadsheet to our circuit drawing (note that the pipe sizes for the red highlighted sections have been added on the next drawing below.)
Now we relabel our sections to follow the blue highlighted route.
Using the blue highlighted water route, repeat the same process used for the red one. Enter the GPM and pipe lengths for each section in the spreadsheet. This time we already know the sizes for sections 1-6, they were entered into the spreadsheet when we did the red section. So we just enter those for the new blue sections 7 and 8, again using 3/4″ size pipe. And it looks like this on the spreadsheet calculator:
Using 3/4″ pipe size for our two new sections works good. The velocity is safe and the Total of All Sections is 3.29 PSI, so the pressure loss for this route is also within the 4 PSI maximum we set. Write the size of the two new sections on the drawing and the blue water route is done.
Now all that remains is to do are the calculations for the magenta highlighted water route. That is done the same way, entering the data into the spreadsheet calculator for each pipe section. Start with 3/4″ then change to larger sizes until the velocity is safe. Then check that the total of all Sections is less than 4 PSI as before. Here’s the data entered into the spreadsheet calculator:
Now all that remains is to insert our lateral pipe sizes from the spreadsheet calculators into the drawing of the valve circuit.
All done! So the pressure loss for the entire circuit is the same as that for the highest water route. In this case the red route was highest at 3.77 PSI. So the pressure loss for the lateral circuit shown here is 3.77 PSI.
Often I get asked at this point why the “Total of all Sections” pressure losses for all 3 routes wasn’t added together? The pressure loss for the red route was 3.77 PSI, for the blue section it was 3.29 PSI, and for the magenta route it was 3.02 PSI. So the confusion is that it seems like there should be a total loss of 10.08 PSI! Nope, the pressure loss for the entire lateral is 3.77 PSI, the loss of the highest route. To understand this think of a single drop of water again. It can only travel on one route from the valve to the farthest sprinkler. It is not going to go backwards and try another route! So the pressure loss for the entire valve circuit is equal to the pressure loss from the valve to the farthest sprinkler.
This method is based on the assumption that you are using Cl 200 PVC pipe for the lateral pipes. With minor adjustments this method will also work reasonably well for SCH 40 PVC pipe or polyethylene irrigation tube. For other types of pipe or tube you will need to use the Trial & Error method to determine the pipe sizes.
While the Pipe Sizing Chart method described here seems rather complex when you read it the first time, it is actually extremely fast and easy once you figure it out. You will start with a simple calculation to obtain a “PSI/100” value. Then you will use that value in the Pipe Sizing Chart to figure out the maximum flow for various sizes of pipe. You will only do this once for each sprinkler system. Once you have that schedule you will fly through inserting pipe sizes into your plan. Most designers who “design in their heads” are using this method or a close variation of it. It is the method I use when designing my systems.
Lateral pipe: The pipes between the control valve and the sprinkler heads are called “laterals”.
Mainline: The pipes that go from the water source to the control valves are called “mainlines”.
Control Valve: The control valve is the valve used to turn on and off a group of sprinklers. Often it is an electric solenoid valve operated by a timer.
Valve circuit: A valve circuit consists of a single control valve, and all the fittings, pipes, and sprinkler heads that it turns on.
GPM: Gallons per minute, a measure of water flow rate. Use primarily in the United States.
PSI: Pounds per square inch, a measure of water pressure. Use primarily in the United States.
BASIC RULES TO KEEP IN MIND
When in doubt, always use a larger diameter pipe!
You may always use a larger size pipe. No, I don’t own stock in a irrigation pipe manufacturer. But using a larger size of pipe will not cause any harm to how well your sprinkler system works. Using a larger pipe will NOT noticeably reduce the water pressure. (Yes, I did condition that statement with a “noticeably”.) The only damage done by using a larger size of pipe is to your pocketbook. Larger pipe generally costs more. But from a irrigation system performance perspective you will NEVER hurt anything by using a larger size pipe. Now I realize that somewhere out there, somewhere will tell you this is not true. They are going to tell you that you need a smaller pipe to squeeze the water and create more pressure. They are totally wrong of course, but as you read this you are probably uncertain who is right, since they will claim I am wrong! Ask them to provide you with a scientific, documented explanation of why they are right. I will also provide both a basic and a very scientific explanation with references for you. Here’s mine: Using A Smaller Pipe to Increase Water Pressure. OK, sorry, I’ll climb down off my soapbox now.
Is it Pipe or Tube? I tend to call everything pipe. Habit, since here in La La Land (Los Angeles, California) we use mostly PVC pipe for irrigation. However some types of “pipe” are technically defined as “tube”. The difference is the material they are constructed of. Steel and PVC plastic are generally called pipe. Polyethylene, PEX, and copper are usually called tube or tubing. If I say pipe where I should say tube, please accept my apologies.
CALCULATING THE PSI/100 VALUE:
The PSI/100 value is a value used in the Pipe Sizing Chart (we’ll get to the chart in a moment.) The PSI/100 value determines which column of the chart you will use when finding the pipe sizes. A simple calculation will give you the PSI/100 value.
The PSI/100 formula:
( ____ PSI x 100) / ____ Feet Total Length = PSI/100
For those who prefer variables, this is the same formula written using variables: (LPSI * 100) / FTL = PSI/100
Here are the values to insert in the blank spots (“____” ), or variables, in the formula:
____ PSI. (LPSI) Insert the maximum PSI loss for all laterals on the valve circuit into the formula where it says “____PSI.” .
If you are working through the Sprinkler Design Tutorial look on your Design Data Form for the Pressure Loss Table. There you will see a figure you entered called “_____ PSI – Laterals”. That is the maximum PSI loss for the laterals, use that number here. If in doubt, 3 PSI is a reasonably safe value for most sprinkler systems. If you don’t understand pressure losses in irrigation, see the Pressure Loss & Selecting Your Sprinkler Equipment and Lateral Pressure Loss pages. Remember that the maximum total pressure loss between the valve and the last sprinkler may NOT exceed 20% of the sprinkler head operating pressure. Example: 20 PSI sprinkler operating pressure. 20 x 0.20 = 4 PSI maximum pressure loss in circuit laterals.
____ Feet Total Length. (FTL) Insert the distance from the control valve to the farthest sprinkler in the space labeled “____ Feet Total Length” in the formula.
For this value you need to figure out the total length of pipe (in feet) that the water needs to travel through in order to get from the valve to the farthest sprinkler. Measure only the pipe sections that the water would pass through on the way from the control valve to that farthest sprinkler. Don’t add in the length of any side spurs going off to other heads that aren’t on the longest route. In the example below, the route from the control valve to the farthest sprinkler that you would measure the distance of is shown in red. Totaling each of the pipe sections along that route results in 118′. So 118 feet would be the ___ feet value you would use in the PSI/100 formula.
Example of A Typical Valve Circuit
Now use the PSI/100 formula above to calculate the PSI/100 value. ( ____ PSI x 100) / ____ Feet Total Length = PSI/100
Write down the PSI/100 value. ____________
Example: Let’s say the value “____ PSI – Laterals” is 4 PSI. Let’s also assume that the total length of the lateral as measured above is 118 feet. Those values inserted in the formula would look like this: (4 PSI x 100) / 118 feet Now do the math. 4 times 100 = 400. Then 400 divided by 118 = 3.389 Round that number to 3.4. Therefore when using this example your PSI/100 value to use in the Pipe Sizing Chart would be 3.4 PSI/100 .
You can repeat this procedure for each valve circuit. But the usual method is–
It is possible to use the same PSI/100 value for all the valve circuits. That’s how most professionals (myself included) do it. The only catch is that you must use the “worst case” PSI/100 value. In other words you need to figure out which of the valve circuits on your entire sprinkler system has the longest “Feet Total Length” between the valve and last sprinkler. Then use that valve circuit to calculate your worst case PSI/100 for the entire sprinkler system. The advantage of using the same PSI/100 value for everything is uniformity of design and, obviously, doing only one PSI/100 calculation for the entire sprinkler system saves time. For example, a pipe with five half circle spray heads downstream would always be the same size pipe. This is much less confusing for the installer, which is the main reason we do it this way.
Pipe Sections and GPM:
Each section of lateral pipe may be a different size. For example, the first section of pipe leading away from the valve might be 1 1/4″. The next two sections might be 1″, and the rest of the sections might be 3/4″. The pipe size to each section is based on the actual GPM flow passing through that section of pipe, so you will need to know what the GPM flow is for each section. If you have been working through the Sprinkler Design Tutorial you have already figured this out and written these GPM values down on your plan in an earlier step. If not, you will need to take a few minutes to do this now. See the page on Sprinkler Pipe Layout for instructions on figuring out the GPM for each pipe section.
THE PIPE SIZING TABLE or CHART:
before you use the chart…
Warning: The sprinkler pipe sizing table /chart is based on using Cl 200 PVC pipe. For other pipe types you will need to make an adjustment if you want to use the chart.
Schedule 40 PVC: If you plan to use Schedule 40 PVC pipe (“SCH 40”) for the laterals you need to make an adjustment before using the chart below, because SCH 40 PVC pipe has a much less water capacity than other PVC pipes. Reduce the PSI/100 value you just calculated for the valve circuits to 1/2 the original values.
Example for SCH 40 PVC pipe: In the example above you calculated a value of 3.4 PSI/100. But you have decided to use SCH 40 PVC pipe for the laterals, rather than Cl 200 PVC pipe. So you will need to reduce the PSI/100 value by half. 3.4 x 0.5 = 1.7 PSI/100. So your new value is 1.7 PSI/100. As you will see, this will result in much larger lateral pipes! This is why most people do not use SCH 40 PVC for laterals, and why I recommend you use Class 200 PVC. It makes a big difference in cost!
Class 125, Class 160, or Class 200 PVC pipe: The chart below is based on the use of Class 200 PVC pipe. It also works for Class 125 (not recommended) and Class 160 (hard to find).
Class 100 and 315 PVC pipe: As a general rule, these types of PVC pipe are not used for laterals.
Polyethylene, Polybutylene: Use the chart below. Then, after you obtain your pipe size from the chart you need to increase it by one size to get the proper size for poly pipe. In other words, if the chart says ¾” PVC pipe, then you should use 1″ poly pipe. 1″ would become 1¼”, 1¼” becomes 1½”, 1½” becomes 2″, etc. Note: PEX pipe is not the same thing as polyethylene irrigation pipe.
To use the chart you will use the PSI/100 value you calculated along with the GPM flow in the pipe section.
Sprinkler Pipe Sizing Chart for Laterals
PSI/100 (round down)
Flows shown in red are over 5 feet/second.
Sprinkler Pipe Sizing Chart, Copyright 1979, Jess Stryker, All rights reserved.
Permission is granted for reuse for any purpose and in any media, provided the copyright notice is maintained.
Sprinkler Pipe Sizing Table /Chart Instructions:
Start with the pipe section farthest from the valve (connecting to the last sprinkler head.)
Find the PSI/100 value in the top row (blue text, directly under the heading PSI/100.)
Read down that column and find a value equal to, or higher than, the GPM in the pipe section.
Now read across to the right column to find the pipe size to use for the pipe section.
Repeat steps 3-5 for the other pipe sections in the lateral valve circuit.
Flows over 5 ft/second are considered marginal (shown in red on chart.) Most experts believe that flows up to 7 ft/sec are acceptable for laterals. However flows over 7 ft/sec velocity are not considered safe, so they are not shown on the chart.
This table uses an averaging formula based on the assumption that all flows for any given size of pipe will not be at the maximum GPM for that size of pipe. In rare cases the PSI loss for the entire lateral may exceed the desired loss by up to 10%.
This table assumes the use of Cl 200 PVC pipe, adjustments to the pipe sizes are required for other pipe types, such as poly or SCH 40 PVC.
In the example above the flows for each pipe section are noted in gray text with an arrow pointing at the pipe section. The red pipe circuit has the longest distance between the control valve and the farthest sprinkler head. So for our example let’s use the red pipe circuit.
First we need to calculate the PSI/100 value.
We start with the maximum pressure loss we want in our lateral pipes. For this example we will use 4 PSI.
Now we measure the total pipe distance from the valve to the farthest head. I showed this route using a bold red line. It is 96 feet from the control valve to the farthest head when following this bold red route.
Now the PSI/100 formula with the values from this example inserted: ( _4_ PSI x 100) / _96_ Feet Total Length = _4.2_ PSI/100
Now we start using the chart to find the pipe sizes.
Our PSI/100 value is 4.2, so we look on the chart. Rounding down we see that 4.0 is the closest PSI/100 value on the chart, so we use the 4.0 column.
Now read down the 4.0 column. The numbers will tell us the maximum flow for each pipe size.
So the first number we see is 10. That would mean 10 GPM. Reading across to the right we see that 10 GPM is the maximum flow for 3/4″ size pipe.
Continuing in the 4.0 column, the next number is 20. Again we read across and see that 20 GPM will be the maximum flow for 1″ pipe.
Reading down one more line we see that 36 GPM is the maximum flow for 1 1/4″ pipe. And we can continue this on down the chart.
So now we can create a simple pipe size schedule to use for our plan, based on the values we took from the pipe sizing chart:
Up to 10 GPM = 3/4″ size pipe
Up to 20 GPM = 1″ size pipe
Up to 36 GPM = 1 1/4″ size pipe
Up to 48 GPM = 1 1/2″ size pipe
Up to 76 GPM = 2″ size pipe
Now go back and look at the flow for each section of pipe on your plan. Then based on the GPM flow, insert the pipe size from the schedule you made.
So the section with a flow of 2.5 GPM will be 3/4″ pipe.
The section with 1.3 GPM will also be 3/4″ pipe.
The section with 3.8 GPM will be 3/4″ pipe.
The section with 6.4 GPM will be 3/4″ pipe.
The section with 1.3 GPM will be 3/4″ pipe.
The section with 2.6 GPM will be 3/4″ pipe.
The section with 9.0 GPM will be 3/4″ pipe.
The section with 11.5 GPM will be 1″ pipe.
I’ve inserted these pipe sizes on the example sketch above.
See how fast and easy that is? Once you have the initial PSI/100 calculations done you can use the pipe sizing chart to create a custom pipe schedule for your plan. Then it is really fast to simply look at the flow in a pipe section, look it up on the schedule, and write in the pipe size! You can see why pros use this method, it allows them to fly through a large design with hundreds of sprinklers.
COMMON PROBLEMS AND QUESTIONS REGARDING USING THE PIPE SIZING CHART
Is your PSI/100 value off the chart? If your PSI/100 value is 6.0 or higher you should use the 6.0 column. At 6.0 you have reached the maximum safe capacity of the pipe sizes used on the chart.
Is the pipe size larger than the valve size? It is fairly normal for the first pipe after the valve to be one size larger than the valve. So you may have a 1″ mainline going into a 3/4″ valve and then have a 1″ lateral pipe coming out of the 3/4″ valve. This is very common, and is not a problem at all. So don’t worry if the pipe size you get from the chart is larger – or smaller – than the valve size.
Write the pipe size down next to the pipe on your plan. Repeat for each pipe section. Repeat for each valve circuit.
There is a very persistent misconception in the lawn sprinkler industry that using progressively smaller pipe sizes in a sprinkler system will help keep the water pressure high. The argument is that as the water moves through the pipes past the sprinklers, the pipe must get smaller in order to squeeze the water so that the pressure stays high enough to operate the sprinklers. Unfortunately, it’s not true. It would be nice if it was, because we could eliminate pumps. Plus think of all the money you would save on pipe. The smaller the pipe you used, the better your system would work! So why not use 1/4″ or even 1/8″ tube for the pipes? That would really pump up the pressure! Sounds a little silly when you look at it that way, right? OK, enough with the sarcasm. I’ll explain this whole mess.
Squeezing the water into a smaller pipe will not increase the water pressure!
Part of the reason this misconception persists is that it does seem logical. The example most often given to support this idea is what happens when holding your thumb over the end of a hose. As you press your thumb over the opening, making it smaller, you can feel the water pressure against your thumb increase. Pushing your thumb even tighter against the end of the hose, makes the opening even smaller, and you feel the pressure increase even more. That would seem to prove that decreasing the opening size is increasing the water pressure. So logically, using a smaller pipe would also increase the water pressure.
Unfortunately there is a lot more happening with this “thumb over the hose end” example than you realize. As water moves through a hose or pipe there is a lot of resistance caused by the hose or pipe surfaces. The water moves through the hose at the maximum speed it can while still overcoming this friction. When the water reaches the end of the hose it has close to zero pressure left as it exits. So if you have, say, 50 PSI of water pressure at the hose faucet, the water will move as fast as it can through the hose, such that it will use up almost all that 50 PSI of pressure by the time it reaches the end of the hose. If there were 60 PSI of pressure, the water would just move a little faster through the hose so that it used up almost all 60 PSI by the time it exits. So basically regardless of the pressure, almost all the water pressure is used up by the time the water flows through the hose. The nature of water is that it will reach the most efficient balance between flow rate and pressure loss that it can. (Note, I am oversimplifying this to make it digestible for the average person. If you have a degree in hydraulics you already know all the other related stuff about open vs. closed channels and nozzling effects.)
When you put your thumb over the end of the hose you change the flow dynamics in the hose. Your thumb restricts the flow of water through the hose. With your thumb over the end, the water is flowing much slower through the hose, and as a result, there is a lot less pressure loss due to friction. So with less pressure being lost in the hose, the pressure at the end of the hose where your thumb is increases. The tighter you squeeze your thumb, the more the flow is reduced, and the greater the pressure you feel will be. But you haven’t created any NEW pressure. You have simply traded reduced flow for increased pressure. You can easily test this yourself. Take a bucket and time how long it takes to fill it using an open end hose. Now time how long it takes to fill the same bucket with your thumb firmly pressed over the hose end. It will take longer to fill, because your thumb has reduced the flow! The same thing would happen in your sprinkler system if you used smaller pipe to increase the pressure. The smaller pipe would restrict the flow of water. The reduced flow would reduce the pressure loss in the pipes, resulting in more pressure. But of course the sprinklers would not work because they won’t be getting the flow they require! Sprinklers require both flow and pressure.
OK, that’s the layman’s explanation. But there are also some much more complex scientific theory that I have been asked about in relation to this topic. So here’s some very scientific explanations.
Grab your thinking caps for this. As you well know, Bernoulli’s Principle essentially says (paraphrased) that as the speed of a fluid increases, the pressure of that fluid decreases. If it didn’t, pigs wouldn’t fly.* Obviously as you force a given amount of water through a smaller size pipe, the velocity of the water must increase for it to get through the smaller pipe. According to Bernoulli’s Principle that will decrease the water pressure! This is called the Venturi effect. By suddenly forcing the water through a narrow passage you can actually create enough of a pressure decrease that it creates suction. This is how many fertilizer injectors work. It also is another reason why using a smaller pipe would not increase the pressure– it would actually decrease it!
Another less common argument is the pipe size must be decreased because the flow is decreasing at each sprinkler head location along the pipe route. Thus if the pipe were to remain the same size, the velocity in the pipe would decrease, resulting in an increase in pressure (according to Bernoulli’s Principle again.) This is actually a good, scientifically based point, and accurate too! So the argument is that the pipe sizes must become smaller in order to keep the velocity constant and avoid an increase in water pressure. (Are you bored yet?) Unfortunately when used as an argument for using smaller pipe, this one falls flat when you do the actual math. At a flow of 7 feet per second, which is the maximum recommended safe flow for PVC pipe, the maximum possible pressure increase due to velocity change would be a whopping 1/3 PSI. So in theory, using a smaller pipe would eliminate that 1/3 PSI pressure gain. But using a smaller pipe probably would also increase the pressure loss due to friction, as previously mentioned. The drop in pressure due to friction loss likely will offset most if not all of any gain that might have occurred due to decrease in velocity. Even if it didn’t the maximum possible pressure gain of 1/3 PSI is simply not significant and would not be noticed. So I stand by my statement that the only reason to decrease pipe size is to save money.
*Oh, by the way, Bernoulli’s Principle is why airplane wings create lift, which helps airplanes fly. Therefore, it is also the reason that people, and yes, even pigs, can fly!
Here are some spreadsheets I have created to help you calculate the capacity and water pressure loss through pipes and tubes of various types and sizes. These should be useful for both figuring pressure loss in mainlines and laterals. Each spreadsheet allows for multiple sections of pipe of various sizes and flows. All you do is select the proper spreadsheet for the type of pipe you are going to use, select the pipe size from a drop down list, enter the flow through the pipe in GPM, then enter the length of the pipe in feet. The spreadsheet calculator will then do the math to give you the water velocity in the pipe along with the pressure loss in PSI for that section of pipe. If there are multiple sections of pipe the spreadsheet will also total all of them for the total pressure loss.
Full instructions for using the spreadsheets are included on the spreadsheets.
Please read this paragraph before you try to use the spreadsheets.
These spreadsheets use Apache Open Office. That means you need to have the Open Office program installed on your computer for them to work. I use Open Office because it is a free, safe program that is available for just about every desktop and laptop computer make and model. That means just about everyone can use it, and nobody has to make a major software investment just to use the spreadsheets. If you don’t already have Open Office you will need to install it on your computer before you can use the spreadsheets. You can uninstall it when you are done using it if you want. Download it free from http://www.openoffice.org . It does take a while to download Open Office. It is a full office productivity suite. (Check it out, there are some cool apps in it!)
Your browser may try to “open” the spreadsheets if you left click on the links, even if you don’t have Open Office installed. This is because most computers have some type of minimal spreadsheet reader installed on them, so the reader will try to open these spreadsheets. If they were just simple spreadsheets they would probably work with the readers. But they aren’t. In most cases you will get a corrupted version of the spreadsheet that does not work. This is because these friction loss calculators use very complex formulas that the “stripped down” spreadsheet readers can’t handle. You need to install Open Office. I may have already mentioned this. 🙂
Remember, you can un-install Open Office when you are done if you don’t like it.
If you try to open the spreadsheets directly using your Internet browser they will probably open as Read Only and the spreadsheet won’t work. This is because the browser will not open an executable file directly. (It is trying to protect you from possible viruses.)
Solution: Right click on the link and “Save” the file to your hard drive. The actual wording varies, so depending on your browser you may select “Save link as..”, “Save Target as…”, etc. This should save the spreadsheet file to your hard drive. Then open it directly from your computer without using the browser plug-in. Tablet and phone users: you may need to get to a real computer to use the spreadsheets.
If the spreadsheets don’t work for you..
Do you have Open Office installed? If not, install it.
Are you using Open Office to read the spreadsheet? Sometimes another spreadsheet program will try to open it instead of Open Office.
Have you tried saving the spreadsheet file to your desktop, starting up Open Office, then opening the spreadsheet with Open Office?
If the spreadsheet says it is “Read Only” you probably are using a non-compatible plug in. Install & use Open Office.
Just dragging the spreadsheet link to your desktop may not actually save the file. You need to right click on the link and select Save as…
If you have an older version of Open Office you may need to upgrade it.
Try rebooting. I’ve experienced a problem where if I try to open one of these spreadsheets in a browser the computer gets messed up and won’t start Open Office. Rebooting fixed the issue.
SPREADSHEET CALCULATORS FOR PVC PIPE
Do not try to open these spreadsheets by left clicking on the links. Save the spreadsheets to your hard-drive first. See the explanation above.
Q. How far should the sprinkler line be from a wooden fence? Im gonna run lines next to a wooden fence all around the perimeter of my backyard. Fence is about 8 feet tall.
A. There are several issues here that come to mind. Most of this applies to walls as well as fences.
If your are using a trencher or [plow to install pipe the machine will likely not get closer than 18 inches to the fence. I would stay even further away, maybe as much as 3 feet. Both of these machines have a tendency to slip from side-to-side or get out of alignment when operated, especially by a inexperienced non-pro. You don’t want the machine to go through the fence.
One issue here is future maintenance should you need to dig up the pipe for a repair. You want enough room that you aren’t whacking the shovel handle (or your shoulders) against the fence if you need to dig. That would mean at least a foot of distance from the fence. Maintenance of the fence is another issue. If you spray water on the fence it will shorten the life of the fence, not to mention leaving ugly water stains on it. It is near impossible to remove water stains from a fence.
Sprinkler Heads and Water Stains on the Fence:
The sprinkler heads should probably be about a foot minimum from the fence. The closer they are, the more water they will get onto the fence. The water will
stain the fence and also shorten the fence life. To keep the water off the fence completely means the sprinklers have to be very far from the fence, typically at a minimum 24″ away for spray type, 36″ for the larger radius rotors. There are variables that impact that distance they need to be away from the fence. Different sprinklers have different amounts of accuracy as to the edge of the water pattern. Impact type rotors often spray a lot of water to the side, outside the normal watered area, thus they need to be very far away. In fact, with impacts I would say that you are not going to keep the fence from getting wet, period (unless you keep the head farther away than the radius of the impact sprinkler!) Also wind plays a huge factor in blowing water onto the fence.
Don’t Plant Lawn Next to a Fence!
When I want to keep a fence dry I plant a minimum 3 foot wide strip along the fence with shrubs and water them with drip irrigation (or use shrubs that don’t require irrigation). That way I can keep sprinkler watered lawn at least 3 feet from the fence so the sprinklers are at least 3 feet away. If the area is windy I go with 5 feet distance.
Generally it is considered bad landscape design to put a lawn next to a fence, unless it is an extremely attractive fence that you want to be a focal point of the landscape! Standard practice is to “buffer” the appearance of the fence with a shrub planter along the base of the fence.
Q. I have a shallow well that was drilled this summer and a centrifugal pump pulling up about 15 gallons/min (HAPPY!). The problem, it will only produce somewhere around 30psi (sad!). Am I able to add a booster pump to this setup to produce more psi or should I just forget it and go for a submersible pump? Obviously the booster pump would save me $…
A. You can add a booster pump but it is tricky. The flow range of the booster pump needs to match that of the existing well pump. Using two pumps will probably use considerably more electricity than a single new pump, especially if it is a submersible. Submersibles are by nature more efficient than a centrifugal pump at the top of the well and now you are adding the friction drag of two pumps rather than one. I can’t tell you how much the electricity cost difference would be, that’s beyond my knowledge level. But ongoing electricity cost is certainly something to look at.
Essentially when you couple two pumps together they are going to have to play nice with each other. You don’t want one to over-power the other and do most all the work while the other just causes drag. Plus you need to deal with the wiring issues and how you will start the two pumps. Hopefully they would both stay primed so, in most cases, you could start them both together using the irrigation controller connected to a relay connected to the pumps. You might need two relays if the pumps exceed the capacity of the relay.
Finally you will need to deal with figuring out if and how you will handle problems such as the malfunction of one of the pumps. If one burns out the drag created by the burned out pump could very quickly burn out the other. Hopefully you would quickly notice the problem, since the irrigation system would not work well at all if only one pump was running. But what if you were on vacation when it happened?
You probably should get a local pump professional who knows his/her stuff and has experience with two pump systems to help you if you use two pumps.
Basically if you want to keep this a simple do-it-yourself project I’m thinking buying a new submersible for your well would be the better way to go.
Automatic Valves for Rain Barrels:
Standard solenoid irrigation valves don’t work well with a typical rain barrel. The standard solenoid valves used for irrigation systems simply need more pressure than you have available from a typical gravity fed rain barrel. The higher pressure requirement for the valve is a function of the hydraulics that makes the valve operate. You either need more pressure or you need a different type of automatic valve. If you want to create more pressure you need to raise the height of the rain barrel. For every foot you raise the rain barrel you will create 0.433 PSI. The minimum operating pressure of most irrigation valves is at least 15 PSI, that means the barrel needs to be 34 feet above the height of the valve. That is simply not practical in most cases! Now you understand why those water towers you see in some communities are so tall!
Yes, they do make motor-operated valves that will work with almost zero water pressure. So if you have a drip system already installed on your rain barrel and it is working well, then skip over the pump part below and take a look at the options for Motorized Rain Barrel Valves further down this page.
Drip Emitter & Tube Selection
Most people use drip irrigation with their rain barrels, so this article assumes you are using drip irrigation. (If you want to use sprinklers you will probably need a lot more water pressure, and therefore a larger pump.) The best emitters for the very low pressures in a rain barrel fed system are the most simple emitters, such as those commonly called a “flag emitter” or “take-apart emitter”.
Another popular choice for emitters when using a rain barrel is the adjustable flow emitter/bubbler. These use more water and are even less uniform than the Flag Emitters, but they are particularly good for watering pots of various sizes as you can adjust the flow needed for each pot.
Stay away from higher cost emitters and those labeled as “pressure compensating” as they tend require higher pressures to operate efficiently.
Example of a Flag Emitter:
Use 1/2″ tube if you can and keep the drip tube lengths short. Smaller diameter tubes (especially 1/4″ tube!) and longer tube lengths both increase the amount of water pressure needed and lower the water uniformity between plants. To put it another way; if you use long, small tubes the plants on the end of the tube closest to the rain barrel may drown from too much water while the plants at the far end of the tube may not get any water at all.
Gravity fed drip systems from rain barrels are going to have less uniform water distribution. That’s just the way it is, with minimal water pressure it is very hard hydraulically to maintain uniformity. To make the best out of a bad situation you use larger diameter tubes and keep the barrel as close as possible to the plants so the tubes are not too long, as described above. If that isn’t for you, then the alternative is to use a small pump to create more water pressure. Most people just elect to be content with the low uniformity.
If you want to test the uniformity of your drip system it is very easy to do, simply build your drip system and attach it to your rain barrel. Then place a disposable plastic cup under each emitter and run the system for a few minutes. All the cups should have about the same amount of water in them. If the water in the cups varies greatly then the uniformity is pretty bad. If the uniformity is bad enough that you think it will create uneven watering you can do a simple test to see if more pressure will help by hooking your drip system up to a garden hose. Be careful, the garden hose will provide more pressure than you need, so turn the valve on slowly and don’t turn it on all the way. Empty out the cups and run the test with the cups again. Usually the higher pressure from the garden hose will result in more uniformity between the water in the cups.
Consider Using a Pump for your Rain Barrel! The best way to automate a rain barrel irrigation system may be by not using a valve at all! Consider using a small pump placed on your rain barrel outlet hose. Most irrigation systems do not work very efficiently at the low water pressures typical of rain barrel systems. Thus a pump is often the best solution as it may provide the added benefit of more water pressure. But it’s not cheap to add a pump. If your #1 concern is low cost and you don’t care about things like water uniformity between plants, skip down to the section on Motorized Rain Barrel Valves!
Selecting and Installing a Rain Barrel Pump
Make sure the pump is rated for enough flow to supply your emitters, and enough lift to get the water needed for your irrigation over the top of the barrel. Add the flow rate of all the emitters together to determine the flow rate needed for the pump. For example if you have 15 emitters that are rated at 1gph (gph means “gallons per hour”) then the pump will need to supply at least 15 gph. If the barrel is 5 feet tall then the pump will need to lift the water 5 feet just to get it out of the barrel. But you need to do more than get the water out of the barrel. You need pressure to move the water efficiently through the tubes and push it out through the drip emitters. That requires another 45 feet of elevation. So add your rain barrel height to the elevation needed to power the drip system. 5 + 45 = 50 feet. So you want a pump with the capacity to move 15gph of water and lift it 50 feet.
Some pumps are rated using PSI (pounds per square inch of pressure) output value rather than feet of lift. A simple formula converts feet to PSI. Just multiply feet x 0.433 to get PSI. So a pump with a 50 feet of lift becomes 22 PSI. (50 feet * 0.433 = 22 PSI) So if the pump is rated in PSI it needs to produce 22 PSI.
If you can find one the right size, a submersible pump is the easiest and best method. Unfortunately most are made to be fountain pumps or sump pumps and they don’t create enough water pressure. If you find one that will work for you, attach your irrigation hose to the pump, put the pump in the bottom of the barrel, and run the tube up over the top of the barrel. You will need a air vent at the high point on the tube near the top of the barrel (above the maximum water level) to prevent water from siphoning out of the barrel through the tube when the pump is not running. You can buy an air vent from any drip irrigation store. Or… a very simple and cheap way to create an air vent is to add a drip emitter on the hose at the top of the barrel, so that the water from the emitter drips back into the barrel and is not wasted. When the pump turns off, this emitter will allow air to flow back into the tube and the air will stop the water from siphoning out.
If you don’t use a submersible pump then the pump will be attached to an outlet at the bottom of the rain barrel. Make sure the pump is bolted or screwed down to a firm surface or it will jump all over the place when it runs. The tube from the pump outlet will need to be looped up above the top of the barrel and an air vent (or emitter as described above) installed at the high point to prevent all the water in the barrel from draining out through the pump when the pump is off.
Here’s an example of a pump:
The Little Giant 35-OM pump is made for high pressure applications like commercial carpet cleaners, but it produces good pressure at a low flow, a combination that is great for small drip systems. Amazon doesn’t list the performance chart for this pump so here it is:
40 gph at 70 ft hd
60 gph at 65 ft hd
80 gph at 58 ft hd
100 gph at 54 ft hd
120 gph at 45 ft hd
140 gph at 30 ft hd
Controlling the Rain Barrel Pump:
The pump can be turned on and off by using a timer. A simple lamp or other household electricity timer will often work for an extreme low cost option, however lamp timers are pretty limited. Most timers of this type will only turn on and off the pump once a day, and do it every day. Most people don’t need to water daily, so this could waste water. If you do use a simple timer make sure it is rated for a voltage and amperage that is equal to or higher than the input of your pump.
If you want to use a standard irrigation timer to control the pump you will need to buy a pump relay unit. Irrigation timers output 24 VAC, most pumps use 120 VAC. So the pump can’t be connected directly to the irrigation timer. A relay is used to allow the pump to be turned on by the timer. You can purchase a pump relay made for irrigation timers at almost any irrigation supply store. Make sure the relay is rated for the correct voltage and amperage for your pump. Instructions for installing and wiring the pump relay should be provided with the pump relay.
Multiple Watering Circuits:
Most rain barrels don’t hold enough water to supply more than a single irrigation watering circuit, but in some cases they might. If you need more than one “valve circuit” you can simply duplicate the pump solution above and use two pumps. Multiple pumps may be the least expensive solution for as many as 3 or more irrigation circuits. As an alternative, you can use multiple motorized valves (see below) with or without a pump. Another alternative is to use a single pump that is sized to provide enough water and pressure for a standard irrigation setup using solenoid valves. I would suggest that the pump for this would need to create a minimum of 25 PSI in addition to sufficient flow to supply the largest irrigation circuit. Use a standard irrigation controller that has a “pump start” feature to turn on and off both the valves and the pump. The pump will require a pump relay to control it as described above for the single pump system.
Motorized rain barrel valves:
They do make mechanical motor-operated ball or butterfly type valves that will open at any pressure.
One of the least expensive solutions is a combination timer and valve made for garden hoses. The Toro #53746 Battery Operated Hose End Timer is an example of this type of timer/valve. There are likely other brands available as well. This Hose End Timer uses a motorized ball valve to control the water flow. Most of the time the hose end timer gets the job done when used with a rain barrel… but this is a low end market product and be aware that the quality is low. It may very well quit working after a year or two. On the other hand you can buy and replace a lot of these for the price of a full blown commercial quality motorized valve and timer unit like the ones they use on home floor heating systems.
Here’s a link to the Toro Hose End Timer:
For a more expensive, but more reliable and longer lasting method, use a motorized ball valve made for home hydronic heating systems. This is a method shown to me by “Randy G.” who says he has successfully used the motorized ball valves that are made for hydronic heating systems on rain barrels. I haven’t tested these valves, but I looked over the literature on the Taco valve Randy mentions, and it seems to indicate the valve would work. Per Randy, “the Taco Sentry series are motorized ball valves…, and can be had for $70 or so at most online stores… Honeywell, White-Rodgers, and several other companies also sell ones with similar prices. You can get the Honeywell ones dirt cheap…, but I’ve heard their reliability is lower, so I haven’t tried them – something about oxygen breaking down the rubber over time. And, of course, make sure you get a motorized ball valve, not a heat motor valve, unless you really want to use lots of power and take several minutes to open or close…”
Randy also suggests “Virtually all modern (heating) zone valves are 24VAC, and thus directly compatible with standard irrigation timers, especially the Taco electronic ones that draw relatively little power, good for cheap electronic timers.” So when using a motorized heating valve make sure the motor operates on 24VAC as they come in a variety of voltages and the irrigation controllers only work with 24VAC valves. To find these motorized valves do a search for “hydronic zone valve”. Be sure to note the connection types for the valves, most are made to connect to PEX pipe or be soldered onto copper. You may have to install adapters to fit them to your irrigation system pipes or tubes.
Special thanks to Randy for supplying this helpful tip! If you try these valves for your system I would love to hear your thoughts on them as well.
Almost any major maintenance problem in an irrigation system will cause a unusual pressure level or flow level in your irrigation system. Therefore pressure and/or flow monitoring is a good way to detect problems. Most of the time the response to a abnormal pressure or flow level would be to shut down the system, or possibly to shut down the current valve zone and try another one. Irrigation systems are typically shut down using what is called a master valve. A master valve is a single valve located at the water source that can shut off all the flow of water into the irrigation system. For more details see my article on master valves. On systems with a pump you will probably want to shut off the pump. Sometimes, as with booster pumps, you will need to both shut down the pump and close a master valve.
So what problems might an abnormal pressure or flow indicate? A very low pressure may indicate that perhaps the pump is broken (if you have a pump), an intake screen is clogged, a filter is dirty, a valve failed to open, or a pipe has broken. Abnormally high pressure could be the result of a valve not opening when it should, a dirty filter (if the pressure is measured upstream of the filter rather than downstream) or some obstruction in the pipes. Low flow could indicate a valve failed to open, a filter is dirty, or that a pump isn’t working as it should. High flow could indicate a broken pipe, a broken sprinkler, or a valve that is stuck open. In most cases monitoring either flow or pressure is sufficient as opposed to monitoring both.
How to Monitor Your Irrigation System
There are a number of different ways to detect and respond to abnormal pressure or flows. Following are a few or these. If you would like to suggest other methods, please contact me. I realize this is not an exhaustive list.
Use a Smart Irrigation Controller that has a Sensor Input and Response Feature:
This is probably the easiest way to add pressure detection and response. It is also what I consider to be the preferred method, as it is reliable and gives you the most control. Some high-end irrigation controllers can use an electronic sensor hooked up to the mainline pipe to monitor the water in the irrigation system. Some of these controllers use flow sensors, some use pressure sensors, some can use both types. These controllers with advanced features are typically sold as Smart Controllers and are expensive compared to ones typically found on a residential irrigation system. Prices for these controllers typically start around $300.00 and go up into the thousands for ones that handle dozens of stations. But then you get a lot more with them too. They are sold through professional irrigation supply stores, both online and locally.
WARNING: Be sure the controller will do exactly what you want BEFORE you purchase it! Not all controllers marketed as “Smart Controllers” have these sensor input features, many only work with specific types or even models of sensors, and some controllers may not provide the response options you want or need. You need to research the controller carefully. Don’t rely on a simple check list of features! “Sensor input” can mean almost anything, you need details! I have seen controller feature lists where the unit sounded fantastic and ultra flexible, only to discover after closer examination that the actual response features don’t do what I need or want. Read the actual owner’s manual (most controller manufacturer’s have them available on their websites) to see what the true capability of the controller is. Read the sections of the manual on how to hook up the sensor, then there will also be a separate section on how to program the sensor you should look through. Some controllers allow for time delayed responses, some don’t. If you have a pump you will almost always need a time delay feature to bypass the sensor when the pump is starting up. Even those controllers that do allow you to add delay times may not allow as much or little time as you need. It is critical that you do as much research as possible before you go to the expense and effort of purchasing, installing and programming the controller.
For example, I have a Rainmaster Eagle Smart Controller on my own irrigation system, as well as using it on the majority of the commercial systems I design. This particular Smart Controller has flow sensing capabilities, but it does not have built-in pressure sensing capability. It does have a delayed response allowing delays of 1-6 minutes, but only in one minute intervals. It will also allow the use of one additional simple on/off type sensor (most controllers have a circuit for this type of very simple sensors. A simple rain switch is an example of this type of sensor.) It has an audible “chirp” alarm that alerts you that a sensor response has been activated. While this particular controller meets my needs, it certainly will not meet everyone’s. Almost every major irrigation company makes a Smart Controller, and each has different features and capabilities. Be sure you are using up-to-date resources when checking out models. Smart Controller models are introduced each year, and often the capabilities of existing models change from year to year, so it is hard to keep up with them.
When using a controller with a pressure and/or flow sensor you start by installing the actual sensor on the mainline pipe. The method varies with the brand and model of sensor, most are pretty easily installed. The sensor is wired to a special terminal on the irrigation controller. Typically the wire used must be a special shielded communications cable, rather than standard irrigation valve wire. Consider installing communications cable in PVC conduit to protect it, as it is very sensitive to even the smallest nicks from shovels, animals digging it up, or rodents chewing on it. Most pressure sensors work by sending a reading of the current pressure to the controller every few seconds. A typical flow sensor has a small paddle that turns as the water flows through the pipe. Flow sensors normally send a signal based on the amount of flow, for example they might send a signal each time 5 gallons of water has flowed past the sensor. The controller then interprets that data from the sensor and responds. In most cases you will pre-decide what the response will be when you set up the controller. For example; if you have a system with a pump, you could program the controller to shut down the irrigation system if the pressure was below 10 PSI for more then 2 minutes during the set irrigation period. The 2 minute qualifier (delay) for shut down would allow the pump time to pressurize the system during start up and also avoid “false alarms” caused by brief dips in pressure.
Using a Simple Pressure Switch with a Pump Operated System:
This method is for those with pumps. What I am describing here is for emergency shut off only. I’m assuming you already have something set up to turn on or off the pump during normal irrigation operation. That might be a standard pressure tank with a pressure switch to control it. Or you may be using the pump start feature on the irrigation controller to actually start and stop the pump using a 120v relay. The new pressure switch we are talking installing in this case is used only to detect pressures that indicate a problem and turn off the pump. So if all is hooked up properly, in the event of blockage or no water going into the irrigation system the pressure will drop and the new pressure switch will shut the pump off.
This method requires that your irrigation system is leak free and can hold pressure for days between irrigations. If the system is not leak free see #4 below.
1. Make sure you have a really good quality spring-loaded check valve on the irrigation mainline pipe. The check valve goes someplace after the pump, but before the pressure switch. A good quality check valve is needed to keep the water from leaking backwards out of the system through the pump. Typically the self-priming feature of the pump is not good enough by itself to do this, you need a separate check valve.
2. You will need to use a pressure switch that works backwards from normal ones used for household water systems, since you want the switch to shut off the pump at low pressure (standard switches used on household water systems turn on the pump at low pressure.) Some switches can be wired to work either way, others can’t. Keep in mind that the low end on many common pressure switches in around 25-30 PSI. That might be a bit higher than you want for a low end shut off, especially if your system will be operating at less than 45 PSI. You don’t want accidental “false” shut offs since the only way to get the system back on will be to manually start the pump and hold it on until the pressure is back above the shut-off level.
3. There a problem to be dealt with. The problem is that valves close slowly, taking as much as a minute or two to close after the controller tells them to. At the end of the last irrigation cycle a typical controller closes the last valve and immediately shuts off the pump. But it takes the valve several seconds up to a minute or two to actually close. During this closing period the system will depressurize. With no pressure in the system the pump will not restart for the next irrigation cycle, because the low pressure shut-off switch is detecting low pressure and shutting off the power to the pump. There are two ways to deal with this.
A. You can fool the controller into keeping the pump running after the last valve circuit has finished watering. Your controller needs to have the capacity for one extra valve on it to do this, so if you have 10 valves you will need a controller with 11 stations. The last station on your controller needs to not have a valve attached to it. Program 1 minute of time on that last station. Now the controller thinks it is operating one last valve, so it keeps the pump running. That will keep the system pressurized while the final valve closes. If one minute is not enough time for the final valve to close then add another minute of run time to that last empty station.
B. Some controllers have a built in delay feature that keeps the pump running after the last valve closes. This feature keeps the pump start circuit energized, which keeps the pump running for a minute or two after the last valve is signaled to close. This gives the valve time to close before the pump is shut off. Some less expensive controllers have this feature. But typically only high-end controllers have this feature, so this method isn’t very practical. If you are going to buy an expensive controller you might as well forget about using a pressure switch and use a Smart Controller and a sensor to shut the system down, as described in the first section of this article.
4. Often a small leak will cause the system to depressurize between irrigation runs. This can be a major problem. The pump will not start if the pressure is low, the low pressure switch is going to shut off the power to it.
If the leak is very small you can install a pressure tank, just like on a typical house water system. Assuming a small leak, the tank keeps the system pressurized. But that only works with a very small leak and it can take a huge pressure tank to supply enough water to keep the system pressurized. If your system has a larger leak you will need to find and repair the leak. If you can’t get the system leak free, you will need to take a different approach, as described below.
You can use a timer to over-ride the low pressure switch, and allow the system to start even with no pressure. You will need a “Time Delay Relay”. The time delay relay needs to be the type that allows the power to flow when energized, then shuts it off after a minute or two of delay. It needs to have an automatic reset. You then install the relay on a bypass wire around the low pressure switch. That way the pump can start even when the pressure switch is “off” due to low pressure. You will need to work with someone knowledgeable when ordering the time delay relay to be sure you get the correct relay, as they make many different kinds.
Using a Pump Controller with a Sensor:
This is essentially the same method as the Smart Controller method I described earlier. Only the “smarts” are in the pump controller rather than in the irrigation controller. Some of the newer digital pump controllers (don’t get confused here, we’re talking about a separate pump controller, not the sprinkler controller) are programmable, they are simply a small computer that operates a relay that starts and stops the pump. You hook them up to a pressure sensor, also to the irrigation controller, and to any other sensor you want (wind, rain, temperature, light, flow, you name it.) Then you can program them to do just about anything using that information input. They can turn off the pump if a low pressure occurs for more than x number of seconds, turn off the pump if a high pressure occurs for x number of seconds, turn on the pump at a given time of day, etc. Pretty much any input you want can cause the pump to turn on or off. The capability depends on the brand and model of the pump controller. The downside is it takes electronics know-how to set the thing up and someone tech savvy to program it. Typically you hook up a laptop to the pump controller to program in the logic, then once it is programmed it runs by itself. The laptop just gives you an interface that is easier to work with. I really can’t give you much more details beyond that, this type of pump control is beyond my expertise, I just have seen pump system experts use them to do amazing things.
Q. I have manual shut-off valves installed downstream from my electronic anti-siphon valves. I installed them to turn off the water to parts of my yard where I grow annuals and only need to water for a few months out of the year. I would really appreciate it if you would explain why valves downstream cause the anti-siphon valve backflow prevention to fail.
A. If there are some sprinklers that are not shut off by the downstream valves (ie; there is always a sprinkler that will be on when the anti-siphon valve is on) then you should be fine. The key to this is that when the anti-siphon valve is closed the water remaining in the pipe downstream of the anti-siphon valve MUST become depressurized. Depressurizing normally occurs when you shut off the anti-siphon valve and the remaining water pressure in the downstream pipes is released through a sprinkler. But if you have a valve downstream of the anti-siphon valve it will trap pressurized water in the pipe between the anti-siphon valve and the downstream valve and not allow it to “depressurize”. Note that sprinkler heads with built-in check valves will also hold the water pressure in the pipe. That is why when using anti-siphon valves you should remove the check valve from at least one of the sprinklers on each valve circuit (normally you would remove it from the sprinkler on the circuit with the highest elevation.) the check valves are easy to remove from the sprinklers, normally you just unscrew the sprinkler cap and lift out the riser assembly. You will see a rubber washer attached to the bottom of the riser assembly, pull it off. That rubber washer is the check valve seal, with it removed the check valve won’t work. Now reassemble the sprinkler.
How an anti-siphon valve works:
The anti-siphon valve works by use of a little air vent that is located on the downstream side of the actual valve. Look at the anti-siphon valve you will see there is a large cap directly above the water outlet of the valve, the air vent is under this cap. If you look closely at the lower perimeter of the cap you will see holes or slits that allow the air to move in and out of the vent. When the anti-siphon valve is turned off the pressure drops in the pipes downstream from it as the remaining water flows out of the sprinklers. When the pressure drops the little air vent drops open and lets air into the pipe right behind the valve. This air goes into the pipe and breaks any siphon effect (“anti-siphon”) so that sprinkler water can’t be drawn backward through the valve into the potable water supply.
(Water from the sprinkler pipes can be siphoned back into the water supply system when pressure is lost in the water supply system. For example, the water company might depressurize their pipes to make repairs. It doesn’t happen frequently, but it does happen. When the pressure drops the flow reverses and water from the sprinkler pipes, along with dirt and other yucky stuff, can be sucked in through the sprinklers and then into the water supply system. When the pressure returns that dirty sprinkler water may go back into the sprinkler system, but it may just as easily go to your kitchen or bathroom sink. So why wouldn’t the closed anti-siphon valve stop this from happening? After all the purpose of a valve is to stop water from flowing through it when it is closed, right? Yes, of course, if the valve is a manual valve. But electric solenoid valves are “directional” valves. What that means is they are designed to stop the flow when the water is flowing in one direction only. When the water flows backwards they don’t fully close!)
What the downstream valve does:
If you have another shut-off valve after the anti-siphon valve, then the water on the downstream side of the anti-siphon valve will stay pressurized even when the anti-siphon valve is closed. This water pressure holds the little air vent in the closed position so it can’t let in air, and therefore the siphon effect is not broken. This means the anti-siphon part of the valve will not work. Even worse, when the little vent is held closed for days at a time due to the constant downstream pressure, it eventually just sticks in the closed position. Then even if the pressure drops the anti-siphon won’t work.
My Friend or Irrigation Person Says This is All Just Something YOU Made Up!
Unfortunately, this wrong practice of installing valves after an anti-siphon valve is pretty common in the irrigation industry. I’ve been called some pretty ugly names over this issue. Fortunately for me, you don’t have to take my word for it. Tell your friend/buddy/pal to read the box the anti-siphon valve came in. It says right on it “do not install valves downstream” or something similar. If you don’t have the box or it didn’t come in one, then go to the manufacturer’s website and find the anti-siphon valve installation instructions. You will find that same warning. Here’s a sample from Rainbird if you want to check for yourself: Rainbird Anti-siphon Valve Operation Manual. See the section that starts with the heading “CAUTION”.
Looping your mainline often allows you to use a smaller pipe size for it, so using a loop system can be financially advantageous on a large irrigated area. A looped mainline also provides maintenance advantages on larger sprinkler systems, and almost all large landscape irrigation systems, like parks and golf courses, utilize a loop mainline layout. For smaller sprinkler irrigation systems they often provide little or no advantages. As a general rule if you have less than 10 valve zones you are not going to get much of an advantage from a looped mainline.
What is a Looped Mainline?
The irrigation mainline is the pipe that runs from your water source to the individual valves that turn on a group of sprinklers or a drip irrigation circuit. When the mainline is looped that simply means that all or part of it creates a continuous loop. Typically a looped mainline starts with a single pipe coming out from the water source (pump, water meter, etc.) then the single pipe splits into two pipes. the two pipes loop around the irrigated area and then rejoin each other to create the “loop”. Zone valves would be located at various points along the loop to supply groups of sprinklers. Normally you would put a isolation ball valve on each leg of the loop at the “split”, the location where the pipes separate into the loop. A third isolation ball valve is placed on the far side of the loop, allowing the loop to be divided into sections. (see the sketch of a looped mainline below) Additional isolation valves may be added anywhere along the loop if desired, to divide it into more segments. The isolation valves allow you to shut down sections of the mainline for repairs while the rest of it may still be operational. For a large irrigation system being able to shut down only a portion of the system for repairs can be very advantageous. Very large irrigation systems may have multiple loops, sometimes one loop will even be inside of another loop.
How to Design a Looped Mainline
When using a loop you should use the same size pipe for the entire looped portion of the mainline. (This is not a hard and fast rule, just a strong suggestion unless you really understand hydraulics!) The pipe leading from the water source to the loop may need to be a larger size than the loop pipe. It is also OK to have mainline “spurs” off of the loop leading to other valves or faucets. While unusual, the pipe size of the spurs may also be larger than the size of the loop pipe if they need to be. Valves for sprinkler zones, faucets, quick coupler valves or any other equipment may be placed anywhere along the loop, as well as on the mainline leading to the loop or even on spurs off of the loop. Normally drinking fountains would be on a separate pipe and not connected to the irrigation system due to the possibility of water contamination from the sprinklers. See the article on use of backflow preventers for more information on contamination.
You can have multiple loops, but I suggest that if you do, you size the pipe using the outside perimeter (largest) loop, as if there were not any cross pipes within the loop (using the method that follows below.) Then after you have determined what size the outside loop pipes need to be, use the same pipe size for any smaller loops or cross pipes inside the perimeter loop. (Technical note: The pipe sizes of inside loops and cross pipes do not necessarily need to be the same size as the outside loop, it is just that using the same pipe size will almost always work. Using a smaller size pipe may work, but it may not. So it is advisable for non-experts to stick with the same size!)
Loop Mainline Calculations
You must calculate both the friction loss AND the velocity for a looped mainline. We’ll go through the process step-by-step. You calculate the pressure loss for the non-looped mainline section from the water source to the beginning of the loop in the normal way (as described in the Irrigation Mainline Tutorial), using the pipe size, flow rate, and length of the pipe section. I suggest that you use one of the the Friction Loss Calculator Spreadsheets I’ve created, they are easier for non-mathematically oriented folks to use than the old manual calculations using charts. Choose the proper spreadsheet for the type of pipe or tube. Then enter the size, the GPM, and the length of the loop. Pressure loss for spurs off of the loop are also calculated using this same method.
Pressure Loss in the Loop:
To calculate pressure loss for the looped section we simply will assume that the water flow splits, and 1/2 of the water is going around 1/2 of the loop and the rest of the water is going the other way around. To do this start by determining the “highest flow GPM” that is found on the looped section. If you are planning to operate only one valve at a time that would be the flow for the largest zone valve to be installed on the loop section. If you will be running more than one valve at a time then the “highest flow GPM” will be the combined flow rate for the largest group of valves that will operate at the same time. Once you have the “highest flow GPM” you calculate pressure loss in the pipe using the calculator. But for the looped portion you will enter 1/2 of that “highest flow GPM” for the flow in the looped pipe and 1/2 of the total loop length (all the way around and back to the beginning) as the length of the pipe. The calculator result is the pressure loss in PSI for the entire looped section.
Total Pressure Loss for the Mainline:
Just total up the pressure loss for the mainline leading to the loop, the pressure loss for the loop, and if you have any spurs add to your total the pressure loss for the single spur having the largest loss value. The total of those is the pressure loss for your entire mainline network.
As mentioned, this method of calculating pressure loss uses an averaging system that assumes that half the water goes one direction to the valve, and the other half goes the other direction. While this is not a perfect method, it works good enough for figuring out the pressure loss. However, the flow doesn’t really split evenly in both directions. In reality the flow balances in each direction based on pressure loss, with most of the flow in the loop going the shortest distance to a valve. So if one of the zone valves is just a few feet from the split point on the loop, almost all the flow will go through that short distance rather than going the long way around and back to the valve. Also in the event you make a repair you may close those isolation valves mentioned earlier. This will force all of the flow in a singe direction through one side of the loop. So we come to the second rule of loops, the pipe size for the looped section must be large enough to handle ALL of the flow in one direction. If it is not, you may create excessive velocity of flow in a section of pipe which can cause major, and very expensive, problems. This means you must check the velocity of the flow while assuming all the flow may go in a single direction around the loop. If the velocity is over 7 feet per second you may create excessive pipe wear and water hammer. Pipe wear can seriously shorten the life of your system, water hammer is much worse, let’s just say you don’t want it. (Look it up if you really are curious.)
Calculate the Velocity:
Using the Friction Loss Calculator Spreadsheets mentioned above enter the pipe size, the “highest flow GPM”, and any random value for the length of the loop. Ignore the pressure loss it gives you, just check the ft/sec velocity result it gives you. The velocity MUST be less than 7 ft/sec. If it is not, you will need to use a larger size pipe for the loop.
That’s it! You should now know how to create a looped mainline. If it seems confusing try rereading it, it is admittedly a bit confusing after the first reading! It really is simpler than it first sounds, be patient, grab some coffee, take your time. Go back and actually work through it one sentence at a time, study the sample sketch of a looped mainline and try sketching your own on paper. Practice a bit with the Pressure Loss Calculator to see what happens when you change the input values. It should start to make more sense.
Q. My pump produces 10 GPM at 45 PSI or 7 GPM at 65 PSI. Do you think the flow is decent for my yard? When I had pro’s quote my job (which is why I’m doing it my self as the numbers were huge) they all said I’d need about 40 sprinkler heads.
A. My gut feeling is that you don’t have enough water capacity from your pump and/or well to irrigate the size of area you have planted in lawn. (Don’t panic yet, keep reading for some suggestions.) 40 sprinklers would be a lot to try to run off of 7-10 GPM of flow. But it depends greatly on your climatic location and water needs. If you only need irrigation for periodic supplemental watering you may be OK. The rule of thumb is that 10 GPM will water about 1/2 an acre of lawn, assuming you need to water about 3 times a week to keep the grass lush. So if you need to water only twice a week, then you could water more area with 10 GPM of water flow. Also, the rule of thumb assumes you only wish to water during the night hours. You could water more area if you are willing to water 24/7 during the peak hot season. Keep in mind that if you share the water use with your house that 24/7 watering might not be a good idea as you won’t have any water left over for use in the house. When your spouse gets in the shower and no water comes out because the sprinklers are using all of it, things are not going to be pretty!
The rule of thumb is that it takes 20 GPM to water an acre of lawn in a hot climate area. So if you have a larger lawn you may need to think about adding a new pump and/or well. I really don’t have enough info to say for sure since I don’t know the size of your yard or your climate location. Take a look at this article which will show you how to calculate how much water you will need for your exact situation: http://www.irrigationtutorials.com/how-to-estimate-water-useage-required-for-an-irrigation-system/
Options to consider if you don’t have enough water:
An option a lot of people in rural areas use is to create watering zones around the property. They heavily water the area right around the house, possibly 25′ or so out from the foundation, sufficient to create a really lush green lawn. Then for the next 25-50′ out they apply just supplemental water, watering maybe once (or twice) a week in hot weather. This supplemental water area would tend to yellow a bit and show stress during the hottest part of the year. Then they have a “no irrigation” area at the far reaches of the property that gets no irrigation water at all.
Tips on designing supplemental water areas: The sprinkler system design for a supplemental water area should be the same as for the lush area. In particular, the distance between the sprinkler heads should be the same for both the lush and supplemental areas. The only difference is that the supplemental area doesn’t get watered as often. Don’t try to stretch out the sprinkler spacings to use less heads in the supplemental area, that will result in problematic dry spots that create a splotchy look to the grass. A splotchy lawn really looks bad. If you space the heads correctly then you will get a uniform looking lawn in the supplemental area, it will just have a yellower tint to it, and it will not be nearly as noticeably “ugly” as a splotchy lawn. Also by designing the supplemental area for “full water coverage” you have the future option of turning that area lush by simply adding a new well or bigger pump. If you skimp on the sprinkler spacing it is really difficult to correct the spacing problem if you ever wanted to make it lush. You can add more heads, but I can tell you that over my 35 years in the business I have never had a customer who was happy with the results of adding more heads. Your only real option to fix a system with heads installed too far apart is to rip it all out and start over. Expensive!!!
Another option: If you don’t have the water supply or money to do all of it right, then install it in phases. Start with the area around the house. Then add more sprinkler zones to water the areas farther out from the house each year as you have funds and time. Add another pump and/or well later when you need the water. The critical thing is to “do it right” in regards to the sprinkler spacing and resist the temptation to stretch spacings between the heads to stretch the water supply or save money. The results are always disappointing if you do that.
Q. Is it possible to have two valves on at the same time or to run two irrigation valves at once?
A. Yes, it is often possible to run two valves at once. However there are several problems that can occur.
You must have a sufficient water supply for both valves to run at once. If the performance of the sprinklers suffers and you start seeing dry spots in the landscape, you obviously don’t have enough water. You may need to do some adjusting of the sprinklers as the water pressure operating them is likely to be less when two valves are on.
Both valves running at the same time may require more water than the pipe supplying them can reasonably handle. This can result in water hammer, or premature pipe wear/failure, due to high water velocity.
Water Hammer: Listen for a loud water hammer “thump” or “bang” noise when the valves close. A gentle thump is fine, but if the pipes reverberate from it that is not good. Run just one valve and listen to the sound when it closes. Assuming the irrigation is properly designed, that should be the “normal” closing sound. Now listen to the sound when both valves are closed together to see if it is significantly louder. If it is significantly louder, that is not good. You can possibly reduce or eliminate the water hammer problem by closing the valves separately, one at a time.
High Velocity: Premature wear due to velocity is harder to figure out. It generally isn’t a problem unless the water is really flowing fast through the pipe, like 8 feet per second or higher. The only way to determine if it is a problem is to do a couple of calculations. Start with the sprinklers. On top of each sprinkler is an identifying names and part numbers that tell you the brand, model, and hopefully the nozzle size. Write down that information for each sprinkler, then look up the water use (GPM value) for that sprinkler and nozzle at the sprinkler company’s website. (You may need to call the company’s help line to assist you, each brand and model is different so I can’t give exact instructions.) Now add together the GPM values for all the sprinklers that are running at the same time when two valves are turned on. This will tell you how much water the two valves require when running together. Next find the size and type of the water pipe that leads to the valves. (For example it might be a 3/4″ copper tube, or maybe a 1″ PVC pipe. It may be several different sizes and types of pipe, in which case you would use the smallest pipe size and type.) Using that information you can calculate the velocity of the flow in the pipe using the Friction Loss Calculator at http://www.irrigationtutorials.com/formulas.htm#sec8. Just enter the pipe type, size, and GPM into the calculator and it will give you the velocity.
If you decide to use a controller to operate the valves the controller must be a brand that provides sufficient amperage to run two valves at the same time (most do.) If you want the controller to run the valves at the same time, but start and stop them about one minute apart to reduce water hammer, you will need a controller that allows you to run two separate valve zones at the same time. Most controllers have a “stacking feature” that prevents them from doing this. You will need a controller that allows you to turn off the stacking feature. Most controllers can’t do this. You will probably need to enlist a knowledgeable controller salesman at a professional irrigation supply store to assist you in finding a controller that will work for this unique situation.
Q. We live on a river. I would love to plant some interesting things on the bank below our home but with the price of water these days I would love to be able to pump some river water up to do the job. Do you think that that is something we could do without spending a fortune? It would be great to have a soaker system.
A. First, you must have the right to take water from the creek, river,. pond, etc.. This almost always means you need to talk with the US Fish & Game Department, State regulators, and possibly the Environmental Protection Agency (or equivalent agencies for whatever country you are located in.) If you take water from a creek or pond or any other natural body of water in the USA without checking on the legal rights and requirements you can get into a lot of hot water, fast. The fines penalties and restitution costs can be enormous. So before you do anything, start doing some calling around. Be safe, not sorry. If you don’t know who to call, try calling the local County or Parrish Planning Department, they should be familiar with the agencies that regulate water and be able to point you to the right people.
Yes, from a physical standpoint it is not difficult to pump the water. The cost depends on how fancy you make it. My parents had a cabin on a river in Oregon. They simply had a small portable pump that sat on a concrete block and was chained to a tree. One end of a 15′ garden hose was attached to the pump intake, the other end of the hose had a piece of window screen tied around it to create a home-made filter and keep out small fish and junk. The end of the hose with the screen filter was tied to a concrete block and dropped into the river. The pump outlet was attached to a second garden hose, this one was 150 feet long. A long extension cord went from the pump to the power outlet at the cabin. They put a sprinkler on the end of the hose, placed the sprinkler where they wanted water, then plugged in the pump. Simple, cheap. You could easily semi-automate that by simply plugging the pump’s power cord into a timer to turn it on and off.
A fancier system is certainly possible. The pump still needs to be portable in most cases. The pump has to be mounted less than 8 feet above the water level (the closer the better.) You need a pad of some sort to put the pump on, but it is best if the pump can be easily moved, especially if the water level fluctuates in the creek or floods. There is also the possibility of using a submersible pump. A submersible should not sit on the bottom of the stream if there is a lot of mud and silt in the water that would get sucked into the pump. If you have a floating dock or a pier an alternative is to place the pump on it (or hang it below the dock in the case of a submersible pump.) Submersible pumps are often strapped to the side of pier pilings. Be sure to read installation instructions for the pump, many pumps have very specific positioning requirements, some submersibles must be installed inside a special sleeve.
You can get about as fancy as you want- using automatic controls to start and stop the pump and also to open and close multiple irrigation valves. Many irrigation controllers have built in circuitry that will start and stop the pump for you using a electrical relay. If you do it yourself, and you need only something similar to my parent’s small pump you could probably install a pump for around $200.00. The price can go up fast as you get bigger and fancier, $1000.00 is not an out of line figure for a pump system capable of watering an acre or so of yard. The wiring for the pump automated controls is a bit tricky, so most people would want to have that part done by a electrician. How much that costs depends on the length of wire needed to reach the pump. One option to look at when you get to larger irrigation systems is a pre-constructed pump unit. This consists of the pump and all of the needed controls for it pre-installed and pre-tested on a metal frame. You just hook up the pipes and wires to it and turn it on.
You may also need a storage tank for the water, especially if you have a small water supply (like a creek.) That way you could pump a small flow continuously from the creek to fill the tank. Once in the tank the irrigation water would either be pumped out of the tank to the irrigation system by a second pump, or if the tank can be located 30′ or so higher than the level of the irrigated area, you could use gravity flow from the tank. (If you want to use sprinklers the tank would need to be at least 60 feet higher to create enough pressure for a small sprinkler.) The tank will probably need to be a lot larger than you think. Typically they are 5,000 gallons or larger. To find out what size tank you will need you need to determine how much water it will take to irrigate your area. See How to Estimate Irrigation Water Quantity Needed for instructions on estimating your water requirements.
One last word of warning before you start: PLAN FIRST, BUY LATER! Don’t run out and buy an “irrigation pump” first! Most pumps sold with the description “irrigation pump” are designed to operate a single sprinkler on the end of a hose. You need to design the irrigation first, then you will now how much water volume AND water pressure the pump will need to produce. The Sprinkler System Design Tutorial takes you through the process of irrigation system design and finding the right pump size. It’s at http://www.irrigationtutorials.com/sprinkler00.htm
Q. I don’t understand why I can’t apply the same guidelines from your tutorial and choose 2 or 3 heads with 70 foot spacing? That would mean a lot less sprinkler heads on my large acreage lawn. Other than not being able to aim them as selectively, I’m missing the reasons I shouldn’t go this route. But you caution against it, so I’m sure I’m missing something.
A. Someplace around 55 foot spacing things start to get all screwy. They do make sprinklers that will shoot that large radius. They are pricey, the cost works out about the same per square foot irrigated regardless of the spacing (funny how that happens!) The problem is there’s just too much wind drift, evaporation, etc. at those wide spacings. Plus to get water to fly those long distances you need big, heavy water drops with lots of momentum. Those big drops just beat the crud out of the lawn, and cause compaction of the soil. Think of what it would be like if a really hard rain storm occurred each time you watered. Where the huge droplets don’t compact the soil they may erode it. Golf courses and parks have fought this problem for years. Most city parks have now settled for 55′ spacing rather than deal with the grief of citizen complaints about dead grass.
The bigger radius heads work better with pasture grasses, where long unmowed grass blades soften the droplet impact and a few dry spots and general “ugliness” aren’t as important.
It also takes lots of water pressure and volume to get that water out there. 70 feet radius means you need 70 PSI and 30 GPM at each sprinkler head. That means probably 85 PSI or more coming out of the pump. Most systems with big sprinklers like that run at over 100 PSI of pressure, which means lots more wear and tear on the system, and a shorter life-span. With those high pressures, design becomes critical, mis-design a single thing and it is unforgiving; water hammer can rip the whole system apart in a big hurry.
Then there is the safety issue. You ever been hit by a 30 GPM stream of water flying from a nozzle at 70 PSI? I have, it knocks you on your butt and hurts like hell! Keep in mind that the really big impact guns used on farms reverse with enough force to kill you if you are struck in the head by the sprinkler arm. Liability is the biggest reason that parks and golf courses are ditching the big water guns for smaller sprinklers.
Bottom line is that using big radius sprinklers just gets really tricky and the results are ho-hum at best. It’s not a good solution in the vast majority of situations. If you do want to mess with it, get professional help with the design. Most of the sprinklers over 70′ radius are only sold by agricultural irrigation dealers.
Q. We typically have hot summers (month long +100 degree weather,) but recently we are also experiencing very cold winters (recently had 0 degree with -17 degree wind chills that froze a lot of pipes in the city.) Do you have any suggestions that would be useful about winterization for Southwest USA irrigation, or any particular materials that are specific to this area I should ask for?
A. This is a situation which occurs all through the southern US, as far inland as Nevada (Reno sees this type of temperature extremes every year), and up the west coast all the way into the Pacific Northwest. In these areas you see overnight freezing, which is typically followed by above freezing daytime temps. To make it worse, it is often necessary in these areas to irrigate during the winter months due to drying wind and high daytime temperatures! In these places we generally don’t winterize irrigation systems by draining the pipes in the winter, as the soil insulates them enough to prevent freezing. Sometimes we bury pipes much deeper in these places, say 18″, to keep them below the frost level. Any above ground equipment will need insulation installed on it to prevent freezing during the nights. So generally I wrap the above ground pipes with foam or fiberglass insulation, extending down underground to below the typical freezing depth. Where exposed to sunlight I wrap the insulation with a high grade pipe wrap tape that is UV resistant, or with metallic tape. Without protection foam insulation degrades pretty fast from sunlight exposure. Do not use standard duct tape, it is not UV resistant and will be a mess within a year or two. For above ground valves and backflow preventers you can purchase insulating covers that can be placed over them like a big bag, (one brand name that comes to mind is Polar Parka) or you can wrap them in fiberglass pipe insulation wrap. Just make sure water can drain out of the bottom someplace, in case there is a leak. Fiberglass insulation must be wrapped with plastic tape or something else waterproof to keep it dry, it will not insulate if it becomes wet. You can also put thermostat controlled electric pipe heaters on the pipes as another option.
The killer problem is when you have hard freezes that last for several days. Insulation doesn’t work very well during long duration freezes, as the cold has time to penetrate the insulation. In areas where freezing weather lasts longer than over-night, but you still need to keep the irrigation system operational, it is a good idea to install electric pipe heaters on backflow preventers and above-ground valves. If you don’t need to irrigate during the winter in hard freeze areas, then you should do a full winterization process that includes draining water from the pipes. For more details on winterization see the Irrigation System Winterization Tutorial.
Q. I’m designing a pump system from a lake and have read and understand your calculation of FT HD needed for pump selection but it seems that the upstream (uphill) pipe diameter would be a factor in the calculation. I was going to use larger pipe to reduce pipe resistance and valve pressure drop but it seems to me the weight of the additional water (back pressure) would be higher for a larger diameter pipe than a smaller one. It must be easier to push water up a 3/4″ column than a 1 1/2 inch column. You mention nothing about this. Excluding pipe resistance, does the pipe diameter play a roll in taxing the FT HD required? Rephrased – Does a larger diameter column of water have any effect on the static pressure or force required to move it?
A. The short answer is that the larger pipe would be better because there would be less pressure loss in the pipe. This is due to less “friction loss” as the water flows through the larger size pipe. The larger amount of water in the bigger pipe has no impact on the water pressure. A smaller pipe may create more friction loss however, so it can be worse than a larger pipe. To find out, you need to calculate the friction loss in the different sizes of outlet pipe based on the flow and pipe size. See the Friction Loss Calculators to calculate the friction loss in pipes.
More detailed answer:
One of the really hard to grasp principles of hydraulics is the relation of volume of flow, pressure, and the weight of water. Odd as it seems a larger pipe will actually be easier for the pump. It’s not the volume of water, but the height it is lifted that matters. In a way this is a variation on the old saying “which weighs more, a pound of feathers, or a pound of lead?” Obviously both weigh a pound! This version could be phrased “which is easier for the pump, 5 GPM in a 1/2″ pipe or 5 GPM in a 2” pipe? Neither because 5 GPM is still 5 GPM regardless of the pipe size! Yes, you would need more power if you were actually lifting more water, also we would need more power to lift the water higher, but neither is not what is happening. The amount of water nor the height we are lifting hasn’t changed.
The other issue here is flow through a pipe. This is the issue that actually makes the smaller pipe potentially worse than the larger. Because the smaller pipe is smaller it is harder to force the water through it. The resistance of the walls of the smaller pipe causes pressure loss as water flows through. this is commonly called “friction loss”. How much friction loss occurs depends on the flow rate and pipe size. Both higher flows and smaller pipes sizes result in greater friction loss. This is the only reason a smaller pipe would be worse than the bigger pipe. How much worse is dependent upon the actual flow rate and pipe size.
As a general rule (ie: not always true, but is most of the time) the pipe size of the pump outlet is almost always smaller than the size of pipe that will provide optimal flow from the pump. In other words, if a pump has a 1″ threaded outlet, it is very likely that a 1 1/2″ pipe would be attached to the 1″ outlet for use as the outlet pipe. Pump manufacturer’s tend to use smaller size inlets and outlets to save money.
More technical answer:
Think about feet of head. As discussed in the Pump Tutorial, the number of feet of water depth determines the water pressure. So 80 feet of water depth equals a pressure of 80 ft. hd. This pressure will be the same regardless of the pipe size. The water pressure at the bottom of an 80′ high 1/2″ pipe is exactly the same as the water pressure at the bottom of an 80′ high 6″ pipe, even though the 6″ pipe holds a lot more water. A pump actually works by creating water pressure. So for the pump there is no difference between pumping into either size pipe, the water pressure required to move the water into the bottom of both pipes is the same. Now the pressure lost as water moves through the two pipes will be different. Assuming a high rate of flow, a lot more pressure will be lost due to friction in the smaller pipe. So for that reason using a larger pipe will be better. Depending on the flow, however, it may be only very marginally better. To find out you need to calculate the friction loss in the outlet pipe based on the flow and pipe size. See the Friction Loss Calculators to calculate the friction loss in pipes or tubes of various types.
The amount of water needed for irrigation depends on many different factors. A reasonably accurate estimate of the amount of irrigation water needed can be made using Eto data for your actual zip code. “Eto” is the amount of water needed for irrigation, based on scientific research. You can find the historic Eto for any zip code in the USA at the website http://www.rainmaster.com/historicET.aspx courtesy of the Rainmaster irrigation controller company, who makes very good “Smart” irrigation controllers. I use one of their Eagle model controllers on my own home. (Rainmaster get a plug from me as well as a big “thank you” for providing the ETo look up service online.) Unfortunately the Eto value only tells you how many inches per day are needed, which for most folks is a meaningless value. It makes more sense if you think about rainfall which is often also measured in inches. If you find you need 0.20 inches of irrigation, then 0.20 inches of rainfall would provide the required water. But most people in the USA want a value in gallons, which requires you to provide a little more information about your yard. Then you plug the values into a simple formula, and do a little multiplication and division on any calculator.
Formula to calculate the gallons of irrigation water needed per day: (Eto x PF x SF x 0.62 ) / IE = Gallons of Water per day
Values for the formula: Eto: Get this from http://www.rainmaster.com/historicET.aspx . Enter your zip code, or a nearby zipcode, and the website will give you the average daily ET value for each month of the year. Use the highest value or the “suggested reference value”. Usually they are the same thing.
PF: This is the plant factor. Different plants need different amounts of water. Use a value of 1.0 for lawn. For water loving shrubs use .80, for average water use shrubs use 0.5, for low water use shrubs use 0.3.
SF: This is the area to be irrigated in square feet. So for a 30 foot x 50 foot lawn you would use 1500.
0.62: A constant value used for conversion.
IE: Irrigation efficiency. Some irrigation water never gets used by the plant, this value compensates for that. I suggest using 0.75 as the value for this. Very well designed sprinkler systems with little run-off that using efficent sprinklers can have efficiencies of 80% (use 0.80). Drip irrigation systems typically have efficiencies of 90% (use 0.90).
A 1500 square foot grass lawn in zip code 85232 (Central Arizona)
Start by looking up the Eto for zip code 85232 at the Rainmaster website, which displays a suggested reference value of 0.3 inches per day using June, the driest month of the year in that area.
Now rewrite the formula inserting your values into it:
0.3 (Eto value) x 1.0 (grass value) x 1500 (sq ft) x 0.62 ÷ 0.75 (efficency factor) = gallons of water per day
Now do the math, just punch the values into a calculator and get your answer:
0.3 x 1.0 x 1500 x 0.62 ÷ 0.75 = 372 gallons per day
We could figure out the average daily water use for other months of the year also. Just use the same formula but insert the Eto value from the Rainmaster website for the month you want to get a valve for.
Remember this calculation just gives you an estimated value. There are many other factors that could make this value higher or lower. When planning for how much water a system that has not yet been designed or installed will use, it would be very wise to allow for error by adding 10% or more to the daily water use needed. It is generally better to have too much water, than to have too little! Play it safe!
A common related question is “how much water pressure will my irrigation system need?” The answer depends on a lot of factors, but as a rule of thumb, I would suggest 50 PSI of water pressure as a good starting point for sprinklers, 45 PSI for drip systems. If you have a large yard and want to put the sprinklers farther than 30 feet apart you will need more pressure. For example, if you want your sprinklers 45 feet apart you will probably need 65 PSI of water pressure. To get a real value you will need to create an actual sprinkler system design. See the Landscape Sprinkler Irrigation System Design Tutorial .
Never buy a pump, sprinklers, or any other materials before your sprinkler design is completed!