Tag Archives: drip emitters

Test to Determine Horizontal Water Movement

Return to the previous page on Drip Emitter Spacing.

 

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.

Emitter Spacing Test Step 1
Make a pin hole in a 2 liter plastic bottle.
Step 2
Fill the bottle with water and place in the middle of the test area. Refill after empty and repeat.
Step 3
Allow the water to soak into the ground for 24 hours, then measure the radius of the area that is moist at a depth of 25mm.

 

 Return to the previous page on Drip Emitter Spacing.

Main page of the Drip Irrigation Design Guidelines

Gravity Flow & Rain Barrel Drip Systems

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.

Flag Emitters
Typical Flag/Take-Apart Emitters, the one on the right is disassembled.
This is a short path emitter, but this brand was sold in a package incorrectly labeled as a “turbulent flow”.
The pen is to show the size of the emitters.

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!

Also please consider these related articles:

Automating a Rain Barrel Irrigation System

How Elevation Impacts Pressure in Irrigation Systems

Drip Systems for Slopes and Hillsides

Slopes create some unique problems for drip irrigation systems. These problems are not hard to solve, but if not considered and/or addressed they can create a mess.

Sample Design:

Drip System Sample Design

Drip System Sample Design Sample Design of a Drip System on a Slope

An easier to read, higher resolution (656 kb) pdf version of the drip system design shown above can be downloaded by clicking on the image above, or click here. The pdf version includes a copy of the planting plan that goes with the drip system. The plans print out on 5 standard letter-size sheets of paper. I suggest you click on the image above to download it and then print it for a visual reference before continuing. (Yes, this is a real design for a site on a hillside overlooking the Pacific Ocean in Ventura, California. No, it’s not my house. Our house has a fine view– of two cats in the yard!)

Type of Emitters to Use:

When installing drip irrigation on a slope or hill side, it is best to use pressure compensating emitters. Pressure compensating emitters apply a more uniform rate of water on slopes when compared to a standard emitter. This is because as the water is pushed in a tube or pipe up a slope the water pressure in the pipe or tube decreases. When water flows in a tube or pipe down a slope the water pressure in the tube increases. As the water pressure changes, it results in a change in the rate of water flow from the emitter. Using pressure compensating emitters solves this problem. I suggest using a diaphragm type pressure compensating emitter. For more information please see the Drip Irrigation Emitters page.

Drip Tube Orientation:

One trick for installing drip systems on slopes is to try as much as possible to keep the drip tubes running horizontal to the slope direction. In other words, try to keep the drip tubes as level as possible. A typical design would have either a pipe or drip tube running from the control valve vertically up or down the hillside. Check valves would be installed at periodic intervals on this pipe or tube (I’ll explain more about the check valves later.) From this vertical pipe or tube, the drip tubes would branch off and run horizontally across the slope to the plants. Does that make sense? No? OK, a picture helps, so take a look at the Sample Design of a Drip System on a Slope at the top of this page. This plan is a map view, so you are looking down at the drip system just like when reading a map. Notice the light gray color contour lines that indicate the slope. The contours are labeled at the ends with the elevation, such as 117.00′, so the line labeled 118.00′ is one foot higher than the line labeled 117.00′. Next, look for the tube that runs up the slope on the left side of the area with the check valves shown on it. Now look for the tubes that branch off it, you will notice most of the emitters are on these tubes, which run more or less horizontal to the slope.

Low Emitter Drainage:

When a drip system is installed on a slope a problem called “low emitter drainage” occurs. Each time that the drip system is turned off the water in the tubes drains out through the lowest emitters. This causes a small puddle to form around the low emitters, and the area around these low emitters becomes saturated and over watered. Sometimes this low emitter drainage is not a problem, it just depends on where the drainage is occurring. If the drainage is occurring in an area where it doesn’t create a problem it is likely not worth dealing with it. However, most of the time the water is going to create a problem, such as a mud pit, mosquito farm, or worse. In the case of our sample design low emitter drainage would cause water to drain out of the emitters just behind the retaining wall. This would be a very bad situation, as the water could build up in the soil behind the wall and the weight of the water could push over the wall. As a general rule, if the difference between the highest and lowest elevation is 0,5 meter (1.5 feet) or less, low emitter drainage is typically not a big enough problem to worry about. If the elevation change is greater than that there are two ways to deal with it.

The first way to reduce low emitter drainage is to use special emitters with built-in check valves. The check valves inside the emitters keep the water from draining out of them when the system is turned off. These special emitters are limited in how much water they can hold back, each brand is different so you need to consult the manufacturer’s literature. A typical emitter with a built-in check valve holds back the water from an elevation change of about 1,3 meters (4.5 feet). What that means is that if the slope or hill is more than 1,3m high the check valve will not be able to hold back the water and some water will still leak out. If this were the case you would have to also use a secondary check valve on the tube, as described below. Many designers don’t bother to use emitters with check valves. They just use standard emitters and put up with a small amount of low emitter drainage. If the change of elevation is more than about 1 meter (3 feet), they will use check valves on the tubes as described in the next paragraph.

The second way to reduce low emitter drainage is to install check valves on the tube at periodic intervals. This is the method used on the sample design. The check valves prevent the water from flowing down to the lower part of the tube(s). This does not completely eliminate the low emitter drainage, but it reduces greatly the amount of water that drains out. It basically spreads the problem out so that the water drains through many emitters rather than just a few. But this is still much better than having all the water in all the tubes drain out through just a few emitters. The check valve is typically a small spring-operated type check valve. A check valve is installed on the tubes at intervals based on the height of the slope. Typically check valves are installed at about 1m (3 feet) of elevation change intervals. The number of check valves needed depends on how many tubes you have running vertically up and down the slope. Thus the reason I recommended having most of your tubes run horizontal. In the sample design I was able to limit the number of check valves to 3 by using a single tube to run up the slope and keeping all the other tubes horizontal. When you install the check valve you need to note that it will have a direction of flow arrow on it, be sure to install it with the arrow facing the correct direction. If the check valve has an adjustable spring tension set to the least possible tension if the water is flowing through it uphill. If the water is flowing through the check valve downhill set it to 0,15 bar (2 PSI). Most spring-type check valves come factory preset at 0,5 bars (5 PSI) so you will need to adjust them down. The manufacturer should have literature telling you how to adjust them.

This page is not intended as a full guide to drip irrigation on slopes. This page is a supplement to the Guidelines and by itself is not a complete guide to drip irrigation systems. Please also read the Drip Irrigation Design Guidelines at the link below.

Drip Emitter Spacing

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.

Test to Determine Horizontal Water Movement

To figure out how far horizontally the water will move in your soil you can perform a simple test which I have described on a separate page. Simple test for determining the horizontal water movement in soil.

Calculating Emitter Spacing

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.

Vegetable Gardens:

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.

Potted Plants:

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.

Drip Emitter Spacing sample drawing
TYPICAL LAYOUT OF DRIP EMITTERS FOR VARIOUS LANDSCAPE SITUATIONS.
Click on the image above for a better quality pdf version of this Drip Emitter Spacing Detail.

Drip Irrigation Emitters

More than you ever wanted to know about drip emitters!

Topics on this page:

  1. Types of Drip Irrigation Emitters
  2. Pressure Compensating vs. Non-pressure Compensating Emitters
  3. Flow rates
  4. Brands & Models
  5. Spitting Emitters
  6. Multi-Outlet Emitters

Types of Drip Irrigation Emitters

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.

Long-Path Emitters

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

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.

Flag Emitters
Typical Flag/Take-Apart Emitters, the one on the right is disassembled.
This is a short path emitter, but this brand was sold in a package incorrectly labeled as a “turbulent flow”.  The pen is to show the size of the emitters.

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.

turbulent flow emitters
Typical turbulent-flow or tortuous-path emitters.
The one on the right is cut open so you can see the jagged turbulent flow path.

Vortex Emitters

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!

Vortex Emitter
Vortex Emitter.

Diaphragm Emitters

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.

Diaphragm Emitters
Diaphragm Emitters.  The emitter on the right has been cut in half to show the round rubber diaphragm disk found inside.
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.

Adjustable Flow Emitter
Adjustable Flow Emitters.  Turning the knobbed body changes the flow, similar to the handle on a valve.
Mechanical Emitter

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

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.

Dripperline
Dripline with factory installed emitter.  Notice the water exit hole and outline of emitter inside the tube.

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.

Flow rates.

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.

 

Installing Emitters:

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.

Spitting Emitters:

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.

Multi-Outlet Emitters.

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.

Drip System Basic Parts – Valves, Backflow Preventers, Filters, Tubing, Emitters, and more

A simple drip system.
Illustration of a very simple drip system.

Valves:

Valves turn on or off the water flow through a pipe.

Isolation valves are manually operated valves used for infrequent shut-off of the water. Typically an isolation valve is located at the water source so the water can be shut off for repairs or shut off during the non-irrigation season. Isolation valves may also be installed anywhere on the irrigation system to allow the shut down of sections for repair, this is common on large systems where shutting down the whole system for a repair would be inconvenient.

Control valves are the valves that turn on and off the water to individual “circuits” or areas of the yard that are irrigated separate from one another. The control valves can be automatic (usually electric-powered using a solenoid) or manually operated (hand-powered, ie; turn, turn, turn!) There may be just one control valve or there may be several control valves on a drip irrigation system. For example one control valve may turn on and off the water to emitters/drippers in a vegetable garden. Another control valve might turn on and off the water to emitters for some hanging pots on a patio. Another control valve might turn on and off the water for the emitters at shrubs around the house. Another could even turn on and off water for sprinklers in the lawn, or water for filling the swimming pool or pond. For more information on valves for drip systems, Drip Irrigation Valves.

Backflow Preventer:

The backflow preventer is a device that prevents dirt, salmonella, dog pee, etc. from being sucked back into your drinking water from the drip system. You need to use a backflow preventer on ALL drip systems. No exceptions! For more information on backflow preventers, why you need one, and a simple guide to which type to use, see the page on backflow preventers.

Pressure Regulators and Pressure Reducing Valves:

A pressure regulator reduces the water pressure and keeps it at a constant level. A pressure reducing valve is another name sometimes used for a pressure regulator, both are the same thing.

Most drip systems operate best at lower water pressures than are common in a typical water supply system. A pressure regulator is used to lower the pressure and then keep it at that pressure, even if the incoming water pressure varies up and down. You probably will need to install a pressure regulator on your drip system if your water pressure is higher than 2,8 bars (40 PSI). Keep in mind that a pressure regulator only reduces the water pressure. It will never increase the water pressure, so if you don’t have enough water pressure a pressure regulator will cause you to have even less!

While the name sounds similar, a “back-pressure valve” is not a pressure regulator and has a different purpose.

There are two general types of pressure regulators used, non-adjustable ones (with a factory pre-set outlet pressure) and ones with user adjustable pressure settings. Either type may be used for a drip system. As a general rule the non-adjustable type are used for small homeowner drip systems that utilize less than 3 control valves. Those people who want the best of everything, regardless of cost, would want to use the adjustable-type pressure regulators, as they allow more flexibility and are usually more accurate.

Inexpensive, non-adjustable-type pressure regulators (see photo below) are most often used for simple home drip systems. They are typically made of plastic and have a pre-set outlet pressure. They often have very specific flow ranges and will not work if used at flows higher or lower than the listed range. Since they are not adjustable, be sure to buy the correct one for the flow and pressure your drip system needs. The non-adjustable-type regulators must be installed AFTER the control valve, so if you have more than one control valve you will also need one regulator for each of the control valves. If a valve is installed after a non-adjustable-type pressure regulator it can result in a pressure surge that can damage your drip system. It has been my experience that when used on systems where very high water pressures are present some of the non-adjustable-type regulators may allow a quick pressure surge to pass through just after the valve is opened. If you experience problems with drip tubing blowing out of the fittings right after the control valve is opened you may be experiencing this problem. Try switching to an adjustable-type pressure regulator.

Non-adjustable-type pressure regulator
Non-adjustable-type pressure regulator.
(Install after control valve.)
Notice this regulator has pipe threads. See the section below on pipe vs. hose threads.

The classic adjustable-type pressure regulator can go before or after the control valve. This type of regulator is most often made of brass or bronze, (some plastic versions are made) and has a large screw on it that is used to adjust the outlet pressure. The adjustable-type pressure regulator you use needs to be the correct size as rated by the manufacturer for the flow range. Unfortunately the sizing formulas they provide are somewhat difficult to understand. As a general rule a 50mm (3/4″) adjustable-type pressure regulator will work acceptably for drip systems designed using the Drip Irrigation Guidelines on this website, provided the regulator is set to reduce the pressure by at least 1,4 bars (15 PSI). It is common for the pressure regulator to be a smaller size than the pipe it is installed on. Adjustable-type pressure regulators are often found in the plumbing department of hardware stores rather than with the irrigation supplies.

The adjustable-type pressure regulators may be installed either before or after the control valves, whichever you prefer. On larger drip systems, with multiple control valves, the valves are often grouped together in one or more locations and a single adjustable-type pressure regulator is installed on the mainline before all of the valves in a group. This cost-saving measure allows a single pressure regulator to be used for several valves.

To operate accurately the adjustable-type pressure regulators require a pressure drop between the inlet and outlet of the regulator. The amount of pressure drop varies depending on flow, at low flows less drop is required. As a general rule most regulators will work well if you set the pressure at least 1,4 bars (15 PSI) lower than the inlet pressure. If the pressure drop is less than required, the regulator tends to not work as accurately, and may allow the pressure to vary up and down considerably.

Adjustable-type pressure regulator
Brass adjustable-type pressure regulator.
The large silver bolt on top is turned to change the outlet pressure.
Using a Valve as a Pressure Regulator:

Can I reduce the pressure by partially opening the control valve and not use a pressure regulator? This is a common question, and the answer is yes, you can. If the water pressure from your water source does not fluctuate, and the temperature of the valve does not change, a partially closed valve will work just fine. A pressure regulator is nothing more than a valve with a pressure sensor attached to it. The sensor opens and closes an internal valve in the pressure regulator to keep the pressure at the outlet constant. So yes, you can use a partially closed valve to reduce the pressure, however you need to be aware of the problems this can cause. Sometimes the vibration of the water passing through the valve will cause the valve to open or close a little over time. The biggest problem occurs when the water is warmer or colder than the valve. The valve will change temperature as the water goes through it and expand or contract, this results in a change in how much water goes through the valve, and that changes the water pressure. If the valve closes due to vibration or temperature change the pressure may be reduced to the point the drip system stops working correctly and the plants don’t get watered. If the valve opens too far the water pressure will be too high. This results in emitters popping out of the tubes and tubing sections blowing apart at the fittings where they connect together. Often when the tubes blow apart they whip around, spraying water all over the place. The worst situation is when there is an open window nearby and the water sprays into the house through the window! So if you are willing to live with those risks, you can use a standard valve in place of a pressure regulator. All you do is open the valve slowly until the pressure desired is obtained downstream of the valve, then leave it at that setting. I suggest periodically checking the valve and water pressure to make sure it has not changed.

Filter:

The filter cleans the water. You should use a filter. Some companies tell you their products don’t need a filter when used with city water, or that it is optional. Optional at the expense of your future time and money! Save yourself dead plants and lots of grief and just install a filter. Drip emitters have very small openings that are easily clogged. Water piped to your house is not free from stuff that will clog your emitters! It contains small grains of sand, bits of rust and scale from pipes, even very small snails (the size of a grain of sand) are very common in city water systems.

I suggest that you use a filter with a 150 mesh screen or one with a higher mesh number like 200 mesh. A good quality filter may be installed before the valve or pressure regulator, but the inexpensive filters often sold for drip systems should be installed after the pressure regulator. A good filter will have a maximum pressure rating of 10,3 bars (150 PSI) or higher. If the package does not list the pressure rating it is probably an inexpensive low-pressure model.

I like to use a top quality filter and install it right at the water source so it protects the control valves and the pressure regulator too. Most valve failures result from sand or rust particles clogging the tiny passages inside the control valves! As long as you need to use a filter, why not get a good one and have it protect the valves too? It will probably pay for itself within 5 years by preventing a valve failure! Use a filter that is the same size as, or larger than, the valve. For more information there is a separate, free, tutorial on filters. Click here for the Filtration Tutorial.

Emitters:

The emitters are what controls how fast the water drips out onto the soil. Most emitters are small plastic devices that either screw or snap onto a drip tube or pipe. Some models are preassembled as part of a tube. The most common emitters sold emit 4 liters/hour (4,0 l/hr) of water. That’s about 1 gallon per hour (1 gph). There are many different types and brands available, they each have advantages and disadvantages listed in the detailed page on Drip Emitters. See Drip Irrigation Emitters for detailed information on what type of emitter is best for your drip system.

Drip Emitter on Tube
Drip Emitter on a tube
(If you guessed the plants are strawberries, you guessed correct!)

Mainline:

The mainline is the pipe that goes from the water source to the control valves. In the illustration of a very simple drip system above the gray colored vertical pipe under the valve is a very short mainline. The mainline pipe may be made of galvanized steel, copper, SCH 40 PVC, SCH 80 PVC, Cl 315 PVC, Heavy Wall Polyethylene (SDR 7 or SDR 9) or PEX. PVC is damaged by sunlight and should be buried or protected. Apply several heavy coats of paint or wrapping PVC with aluminum tape if it is above ground. Polyethylene has a low burst pressure and should only be used for mainlines where local conditions are appropriate and water pressures are lower than 3,5 bars (50 PSI). PEX pipe is a special type of polyethylene made for use with higher pressure, often sold as a replacement for copper tube. It may be used for a mainline, however, be aware that due to a much smaller inside diameter it has poor flow qualities when compared to copper. I recommend that when using PEX you use one tubing size larger than you would use for copper tube. On large drip systems a single mainline might lead to several control valves located at different areas of a yard. On large properties a mainline will be install in a loop around the perimeter of the property. Because the water in the mainline is always pressurized, hose bibs are often installed on the mainline. On a large property with a looped mainline hose bibs are often installed on the mainline at 30m intervals (100 feet) around the property to allow for use of hoses. I like to foliar fertilize my plants using liquid fertilizer from a hose-end applicator, and the hose bibs make this easy. There are also devices called “quick coupler valves” that are essentially a water outlet that is mostly underground. You plug a special coupler with a hose attached to it into the quick coupler valve. They are typically only available from on-line retailers or local irrigation specialty stores. I use them in most of my commercial irrigation systems, the maintenance folks love them.

Lateral and/or Sub-Main:

The lateral is the pipe located between a control valve and the drip tube. Some people use the name “sub-main” for this same pipe. I used the term sub-main in the first version of these guidelines, but have decided to use lateral now to avoid confusion with the names used for sprinkler systems. The lateral pipe may be PVC, PEX, or polyethylene. The lateral is located after (downstream) of the pressure regulator so it is not necessary to use a pipe with a high pressure rating. Class 200 PVC or standard “polyethylene irrigation pipe” work good for laterals. Class 125 PVC may also be used but be careful as it breaks easily. PVC is damaged by sunlight and should be buried or protected. Apply several heavy coats of paint or wrapping PVC with aluminum tape if it is above ground. Many small drip systems do not have laterals, in those systems the drip tube connects directly to the control valve. The illustration of a very simple drip system at the top of this page shows a system without a lateral. Laterals are often used when multiple drip tubes are needed, such as when the irrigated area is too large for a single drip tube. For example a single lateral or multiple laterals might extend from a single control valve to several drip tubes located in different areas of a yard.

Hose Threads vs. Pipe Threads:

Two different thread types are typically found on 3/4″ drip equipment. Hose threads are the type of threads found on garden faucets and garden hoses. The female side will have a soft hose washer in it to seal the connection. Typically they also have a swivel device on the female side, but not always. Pipe threads are the type of threads found on standard pipes. It’s really confusing, unfortunately, and it is not easy for someone without experience to just look at the threads and tell them apart!

How to identify hose threads: If there is a washer inside a 3/4″ female fitting that is a pretty good sign it is a hose thread. (Although there are some specialty fittings that use washers and have pipe threads. For example; sink water supply hoses.) When looking at male threads, hose threads have threads that are slightly larger and are farther apart from each other. There also tend to be a smaller number of threads when hose threads are used and the threaded section of the fitting tends to be shorter. (See photo below.) If you look at male pipe threads you will notice there is a slight taper to the threaded area, the end has a slightly smaller diameter than the back (look real close at the male threads on the left side in the photo below, you can see the diameter increases slightly as you move toward the right.) This works a bit like a tapered cork for a bottle. The taper forces the male pipe threads to bite into the female pipe threads, helping seal the joint as you tighten the connection.

Connecting hose threads to pipe threads: It is best to use a special adapter made to connect them. When you try to connect hose threads directly to pipe threads, it will start out fine and will seem like they fit. But once you get past a couple of full turns you will feel considerable resistance because the threads don’t match. Sometimes with plastic fittings they can be forced together, but most often if you do this the connection will leak (if you force them together there is a good chance of causing unrepairable damage!) A trick that sometimes works for a quick fix when connecting a hose thread to a pipe thread is to put two washers in the joint rather than one. A much better way is to use a special adapter made for the conversion (see photos of adapters below.)

Hose to pipe adapters: They make adapters that have hose threads on one side and pipe threads on the other. They are available in many combinations: male hose to male pipe, female hose to female pipe, as well as male to female versions. There are also versions that convert to 1/2″ pipe threads rather than 3/4″. Any good hardware store should have at least a couple of these combinations available. A good suggestion is to “mock up” your connections by screwing them together slightly in the hardware store before you buy the parts. That way you know they will fit. To help you read labels, common abbreviations used in hardware stores are:

  • MHT = Male Hose Thread
  • FHT = Female Host Thread
  • MPT = Male Pipe Thread
  • FPT = Female Pipe Thread.
  • Pipe = Pipe Thread
  • Hose = Hose Thread

Remember to use Teflon tape sealer on male pipe threads to prevent leaks. Avoid liquid pipe thread sealants on irrigation systems, excess sealant breaks loose inside the pipe and clogs the emitters and sprinklers. You don’t need Teflon tape on hose thread connections, they should have a hose washer that seals them.

Thread adapters
Pipe Thread to Hose Thread Adapters
Pipe threads are on left, hose threads on right
Top is a MPT x MHT adapter, bottom is a FPT x FHT adapter.

Drip Tubing (Drip Hose):

Drip tubing is a special tube used in most drip systems. The tube is laid on the ground surface between the plants. The emitters are installed on this drip tube. Drip tubing is a thin-wall polyethylene tube (thinner than standard polyethylene hose), has a low pressure rating, and is generally produced in metric sizes. Sometimes it is called drip hose or drip pipe. Common sizes are 12 mm (0.455″ or 3/8″), 16mm (0.620″ or 1/2″), 18mm (0.720″ or 1/2″), and 24mm (0.940″ or 3/4″). Do you see the problem? Two sizes are commonly referred to as “1/2 inch” in the USA! The fittings for these two are not interchangeable. So make sure you know what you’re getting when you buy it! Do not bury drip tubing underground- gophers and moles love to chew on buried drip tubing! Some drip systems do not use drip tubing. These systems are commonly called “hard-piped drip systems” and are used mostly for very high quality drip systems in commercial landscapes. On a hard piped drip system the emitters are installed directly onto the laterals. This requires special emitters with threaded connections rather than barbs. For a drawing showing how a hard piped emitter works see Rigid Pipe Emitter Installation Detail.

Drip Tube Fittings:

Fittings (including tees, couplings, ells, and adapters) are the plastic connectors used to attach the drip tube to other tubes, to control valves, or to pipes. Important- make sure the fittings are the exact right size! Using fittings made for a different tubing size will result in the tube blowing out of the fitting. 9 times out of 10, when a tube blows out of a fitting it is because the fitting is the wrong size. If you use a 15mm fitting on 16mm pipe you are going to have problems. Remember, both 15mm and 16mm tube are often labeled as 1/2 inch size in the USA!

Barb type fittings insert into the drip tube. Generally they should not require the use of a hose clamp to hold them on, if a clamp is needed the water pressure is too high or the fitting is the wrong size. The advantage of barb fitting is that they are generally easier to install than the compression type. The disadvantage of the barb type is that as the tube goes over the barb it is stretched, which weakens the tube. The weakened tube will sometimes split open at the barb after a few years, especially if exposed to sunlight. OK you ask, if barbs are a problem then why do they use barbed fittings with standard polyethylene pipe? Standard poly pipe has a much thicker wall than drip tube and doesn’t stress as much when stretched. You also clamp standard poly pipe to the fittings, which helps keep the pipe from splitting (that’s why you need to clamp poly pipe even if it seems to stay in place without the clamps). Drip tubing is not clamped to the fittings (clamping doesn’t help prevent splitting because of the thin drip tubing wall).

Compression type fittings are basically the reverse of a barb fitting. The tube slides inside the fitting, where an internal barb compresses the tube and holds it in place. The advantage of compression fittings is that they do not stretch the tubing, so they are not a cause of premature failure of the tube. Once the tubing is inside a compression type fitting it is very difficult to remove.

As a general rule, barb fittings are best used for buried or covered tubing (the tube is not exposed to sunlight) and compression fittings are used for tubing that is not buried.

Drip Tube Fittings
Drip Tube Fittings
Left: Barbed Type Right: Compression Type

Lubrication: Some people just don’t have the strength to shove the tubing into a compression fitting. First make sure the fitting is the right size, as that is very often the problem. If it is, then you can use a water soluble lubricant on the tube. Do not use oil, silicon sprays (WD-40) or soap! Absolutely do not heat the tube with a flame, hair dryer, or hot water as that will stretch the tubing and create weak spots! What’s a water soluble lubricant? Try a product called K-Y Jelly. Attention guys! Avoid terminal embarrassment! Do not head for the hardware store for K-Y Jelly. Try the drug store, err, lady’s personal hygiene department. Might want to take along the wife. Need I say more?

Spaghetti, Feeder, and/or Distribution Tubing

Feeder Tubes, Spaghetti Tube, and Distribution Tubing are all names used for small diameter poly or vinyl tubes, anything less than 10mm (3/8 inch) in diameter. I love spaghetti to eat, but I hate it for use in drip systems! The problem with these small tubes is with maintenance. These little tubes tend to be easily cut, broken, pulled loose, etc. and are generally a nuisance. This small tube is often connected to the outlets of multiple-outlet emitters. This tubing is the reason I do not recommend the use of multiple-outlet emitters. If you are a meticulous type person who can be very careful, do your own yard maintenance, and you don’t have pets or kids in the yard, you may not have any problems. But for most of us, regret soon sets in as repairing these small tubes becomes a weekly maintenance chore. There are a couple of exceptions where the tubes work well. One is when they are stapled above ground to a trellis or arbor for watering hanging plants. They need to be firmly attached, in a location where they will not be damaged. The other is for risers used on hard-piped drip systems.

Air Vent:

The purpose of an air vent is to prevent air from being sucked into the emitters when the system is turned off. When the drip system is turned off the water in the pipes drains down to the lowest point, where it drains out of the emitters. As the water drains out it is replaced with air that is sucked into the tube through the higher emitters. As the air is sucked in, dirt may also be sucked in with it. The dirt may then get stuck and clog the emitter outlet. The purpose of the air vent is to allow air to be sucked in through the vent rather than the emitter. When used, the air vent is installed at the highest point on the drip tube. It is important to make sure that the air vent will not become covered with dirt or dirty water as that would allow dirt to be sucked into it. Always use air vents if the drip system is installed on a slope, as the elevation change creates a more powerful suction that will suck in more dirt. Air vents often are not used on smaller drip systems. If you don’t use them just make sure the highest emitters aren’t sitting where dirt can easily be sucked into them.

Air Vent
A small air vent designed for a drip system.

Flush Valve or End Cap:

The end cap is important. Without it the water all runs out the end of the drip tube. (Well, duhhh…) The water in a drip system flows very slowly in the tubes. This allows any sediment in the water to settle out, over time a layer of this sediment develops inside the tube and needs to be flushed out. In some climates algae may also grow in the tubes and need to be flushed out periodically. Normally drip tubes are flushed once a year. If you have algae problems you may need to flush the tubes more often. Automatic flush valves are available that flush the tubing each time the water is turned on. I do not feel that most of these are particularly effective. They simply do not flush for long enough or flush enough water out to remove much, if any, sediment or algae. My preference is to use a manual flush valve, or just use a simple hose-thread cap that you can remove to flush the tube. Here’s a money saving tip; you can make a end cap/manual flush valve by just bending over the end of the drip tubing on itself to crimp off the flow. Then use some wire or a cable/zip tie to hold the tube in the crimped position. Un-crimp and straighten the tube when you want to flush it.

End Crimp
Tubing end crimped with a cable tie.
For very high end drip systems with lots of algae or sediment you may want to build your own auto flush unit. This is an expensive project requiring a high level of skill and knowledge! Manifold the ends of the drip lines together, so that a single flush outlet can flush the entire drip circuit. Install a anti-contamination type solenoid valve as the flush valve on the end of the flush manifold. (An anti-contamination valve is a special irrigation valve made for use with dirtier than normal water.) Wire the flush valve to an irrigation controller and program it to open the flush valve on a periodic basis, typical might be for 2 minutes once a week. The drip circuit control valve must also be on during the flushing. So both the control valve AND the flush valve must be activated at the same time. Do not wire them together on the same controller circuit as that will cause the flush valve to remain open all the time. You will either need to use two controllers and then coordinate the times on them, or you will need a controller that can run two valves on two different programs at the SAME TIME. Warning; most irrigation controllers can’t do this. I suggest you take these instructions and go to a professional irrigation dealer and have them assist you in your controller selection. Make sure you have someplace for the flush water to go, as it will release a lot of waste water when the flush valve opens. Keep in mind that both anti-contamination valves and the special controller you need to use are expensive and this is not a very cost effective solution in most cases.

To return to the main page of the Drip Irrigation Design Guidelines click here.

Can I Just Punch Holes in a Tube to Make Drippers?

Q.  I’m installing a drip irrigation system and to save some money, I decided to buy inch wide black tubing.  I used a hot needle to make some small holes every 27 inches apart from each other, but when doing water pressure testing , some holes emit more water than others.  What do you recommend in this case? Is it a bad idea to punch my own holes?  Or is there a way to do this with an even result in each hole?

A.  Just punching holes doesn’t work well, as you discovered.  It’s almost impossible to get the holes uniform in size, and even if you did, variations in the water flow patterns inside the tube would make each hole emit water at a different rate.  The solution is simple.  You need to install barbed drip emitters in the holes.  The drip  emitters are small, plastic, highly-engineered devices that regulate how much water comes out, so that each hole gives a very uniform rate of flow.  A typical emitter (sometimes called a dripper) is about the size of 5 dimes stacked on top of each other.  The emitter has a barbed inlet on one side that pushes into the holes in the tube.  You just snap the barb into a hole punched in the tube.  Then the water drips evenly out of an outlet hole on the other side of the emitter.  You need one emitter for each hole.  Emitters are typically sold in packages of 10, 25, 50, or 100 emitters per package.

Since you already bought tube, cut off a small piece of your tubing that has a hole in it and take it with you to the store.  1″ black tube is probably not made for use with drip systems.  It probably has a thicker wall than standard drip system tubing, so the barbs on some brands of emitters may not be long enough to push all the way into the tube and lock in place.  Most brands should work, but in your case it would be best to test it at the store so you don’t have to make another trip back to the store if the emitters don’t fit.  The emitter’s barb should push all the way in and lock the emitter onto the tube.  It should not easily pull out.

It might be a good idea for you to read the Drip Guidelines at https://www.irrigationtutorials.com/drip-irrigation-design-guidelines-basics-of-measurements-parts-and-more/ .   There are a lot more mistakes you can make, and I’d hate to see you waste any more of your time and money.

Drip emitter installation tools.

Q:  Have you come across tools to insert drippers in tubes or pipes?  Pushing the dripper’s into the tube is leaving my fingers bruised.

A:   You’re right, some of the hole punches are better than others.  I have one that has a nice big grip handle on it that is easy to hold.  But another inexpensive hole punch I have simply has a rounded top that you press with your palm to force the punch into the tube.  It makes your palm sore after just a few uses.  Pressing the emitters into the holes can be a pain too.  Inserting a couple dozen emitters into the holes can leave your finger tips hurting!  Some emitters have irregular, rough, or sharp edges that make it even worse.

Fortunately there are many tools made to help you out.

There are any number of simple hole punches.  Some are small and hard to hold, some have larger handles which makes them a bit easier.  All of these are very simple tools, you hold them in your hand and press a sharp tip through the wall of the tubing, a bit like an ice pick would work.  Actually an ice pick would work to make a hole, however I have found that any type of pointed punch tends to be too aggressive; it punches a hole through one side of the tube and out the other, making two holes!  Then you have to put a goof plug in one of them to plug it up.

Another thing to consider is the shape of the hole punched.  Most punches actually create a round hole about an 1/8″ in diameter.  Some create holes as large as 1/4″ for specific brands of emitters with larger barbs.  It is much easier to get the emitter into a round hole than one made with a pointed tip, such as a nail. When holes are made with a pointed tip the plastic tube tends to stretch as the tip goes through it.  Then the hole closes back up when you pull the tool out, the resulting small hole is hard to get the emitter barb into.  Also a pointed tip is more likely to tear the tubing wall as the tubing stretches around the tool, creating something more similar to a slit than to a round hole.  There is some debate as to if these tears in the tubing will enlarge over time (similar to how a tear in a plastic bag sill get larger if you pull on it.)  I tend to think you are better off with a round tipped punch that punches an actual round hole in the tube, as opposed to a pointed tip.

Note that any punch that you hold with your finger tips, or press a small “knob” with your palm to operate, is going to be hard on your fingers or palm if you install more than a dozen emitters at a time.  These super cheap punches work fine for a few emitters, but beyond that… ouch!

There are more sophisticated hole punch tools, like the Miracle Punch.  It holds the tube firmly in place which aligns the hole properly.  It operates similar to a pair of pliers, which is much easier on your hands.  There is at least one other “pliers type” tool I have seen on the market, however it does not hold the tubing as firmly.

There are a number of devices made to install the emitters.  Most of these are product specific, that is they only work with a particular brand and model of emitter. They generally have a handle on one end and a molded cradle that you place the emitter in on the other.  You place the emitter in the cradle and then press it into a hole you have already punched in the tube using a hole punch.  Some of these device have both the hole punch and emitter insertion cradle as part of the same tool.

Some companies, like Rainbird, make emitters that are “self punching”.  The barb on the emitter is sharp enough to create it’s own hole when pressed hard against the tube.  Rainbird makes a tool that you place the emitter in, then using the tool you press the emitter into the tube.  My experience is that you need this tool to use the self-punching feature of the emitter.  Without it I have not had much success getting the emitters lined up correctly and pressing them in with your fingers is near impossible.  You don’t have to use the tool to insert the Rainbird emitters, it works fine to punch a hole first using a punch and then stick them into the hole.

TIP: Try wearing heavy leather gloves when installing the emitters to reduce hand pain.  Also try putting a couple of pieces of cardboard in your palm between the hole punch and your hand, to help distribute the pressure over a larger area of your palm.