Whether you’re a professional landscaper or want to irrigate your own yard, this free Landscape Sprinkler System Design Tutorial is designed to take you step-by-step through the process of creating a professional-quality sprinkler irrigation plan, layout, or drawing.
There are lots of Sprinkler Design Guides, Why This one?
This tutorial works with ALL sprinkler products and does not base your design on the use of a single manufacturer or store’s products. Most tutorials will force you into using specific products on your plan. Sometimes they are good products, sometimes not. Bonus: This tutorial will teach you how to spot the really bad irrigation products.
This tutorial assumes you know nothing about irrigation and breaks it all down for you (but the beginner stuff is easily skimmed over for those more experienced.)
This tutorial is multi-level. Many of the topics start with a outline of the topic, then expand on that outline in detail for those who need more explanation. Finally some subjects then move on to cover special situations or layout that are not “typical” for those who need that additional insight. So while some tutorial pages are long, you may not need to actually read a lot of it. Unless you are a future irrigation professional and interested in learning all about irrigation, which leads us to the next point…
This guide is complete. It is used by colleges to teach irrigation design courses, and we encourage that use. However, it is written using 6th grade level English, so don’t panic. If you were ever a broke college student you can probably appreciate the idea of a free online textbook! Speaking of free…
If you have a well and/or pump this is one of the only sprinkler system design guides available anywhere (including those $$$ books for sale at stores) that will show you how to correctly design your system so that it will not destroy your pump by making it cycle or run dry.
Thousands of people have used this tutorial to create their irrigation systems drawings. This tutorial has been online a while, the first version was written back in 1995. You may find an error or two in it (especially in the grammar, it was written by an irrigation expert, not an English major) but most of the technical errors have been found and corrected long ago. Tons of feedback have resulted in rewrites of the parts that were not clear. The advantage of being online is that the tutorial does get constantly updated to incorporate new products, ideas, and methods.
This tutorial was written by a professional irrigation designer and licensed landscape architect who has over 35 years experience designing irrigation for everything from small tract yards to golf courses. More on the author at the bottom of this page.
Warning: There are lots of online tutorials and this one may not be your choice and that’s fine. However there are a number of design guides around, both online and in stores, that use outdated design methods. Please watch out for these major design errors that may lead to very expensive repairs:
Beware of measuring flow with a bucket or gauge. The “GPM” value for your new sprinkler system should be based on the size of the existing water supply pipe running to your house. Some do-it-yourself sprinkler system guides have you measure water flow by turning on an existing faucet and timing how long it takes to fill a bucket. Some also suggest using a special gauge that measures the flow. Regardless of how you measure the flow, we now know that just measuring the flow from a faucet results in major errors that can result in your using a irrigation system flow that is way too high for your house’s plumbing to handle. When you turn on a faucet the water from it will often flow out at a rate that is way higher than what is safe for the pipe’s in your house. While running water for a few minutes at this flow to fill a bucket is relatively harmless, running a sprinkler system at that flow on a regular basis is not. This unsafe high flow results in “water hammer” and “scrubbing” damage to the pipes, two very expensive problems that can destroy the pipes in your house. We are talking thousands of dollars to re-pipe your house! The key here is that when determining the water supply volume the pipe size must be a factor considered.
Sprinklers should have almost 100% overlap. If a sprinkler layout guide shows you coverage arcs that are not going almost all the way from one sprinkler to the next it is based on the old way of doing things back before we had low-flow sprinklers to conserve water. Almost all experts now agree that there should be near 100% overlap of sprinklers. Back in the old days we just told people with dry spots to run the sprinklers longer. That over-watered 90% of the lawn but it greened up the dry spots. We now know it wastes water and even worse, over-watering causes lots of landscape diseases!
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.
Most of the pages of the tutorial are written as stand-alone articles, so that they will be useful to those who do a search for specific information. For this reason there is a small amount of repetitive material throughout the tutorial.
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!
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.)
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.
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.
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. 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.
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