Emitters are classified into groups based on how their design type and the method they use to regulate pressure. You can create a very simple emitter by drilling a very small hole in a pipe. However, a hole alone does not work well. Unless the hole is extremely small, the water tends to forcefully shoot out of it like a tiny fire nozzle and way too much water will come out. More importantly, there is little uniformity of flow when using a simple hole. If you have a long pipe with holes drilled in it the holes on the end nearest the water source will have a large water flow from them, while those at the far end will have a very small flow.
Since using a simple hole in a pipe does not work very well, the early pioneers of drip irrigation started playing around with mechanical devices that would better regulate the flow. These devices have been given the name “emitters” (or sometimes “drippers” is used.) The emitters are installed on the pipe and act as small throttles, assuring that a uniform rate of flow is emitted. Some are built into the pipe or tubing, others attach to it using a barb or threads. The emitter reduces and regulates the amount of water discharged.
There are many different methods used by emitters to create and maintain this uniform, low, flow rate. Some emitters route the water through a very long, narrow passage or tube. The small diameter and great length of this path reduces the water pressure and creates a more uniform flow. These are called long-path emitters. A typical long-path emitter has a long water path that circles around and around a barrel shaped core. Long path emitters tend to be fairly large in size due to the need to fit that long tube in!
Soaker hose, porous pipe, drip tape, laser tubing
Soaker hose, porous pipe, drip tape, and laser tubing are various adaptations of the “extremely small hole in a pipe” type of drip system. They just have very small holes drilled (usually using a laser) into a tube, or are made from materials that create porous tubing walls that the water can slowly leak out of. The advantage of these is obviously very low cost. The disadvantage is that the tiny holes are very easily clogged, especially with hard water containing lots of minerals, and for some products watering uniformity can be uneven. These types of systems are most often used in landscapes for portable irrigation (moving the tubes around the yard between irrigations tends to break the mineral deposits loose so they don’t build up. These products are also widely used in agriculture, where the tubes are removed and thrown away or recycled at the end of each growing season. My experience with permanent installations of these products has been that they have a fairly limited lifespan when compared to other drip irrigation types. They work best with water that has very low mineral levels.
Short-path emitters are similar to the long path emitters. They just have a shorter and smaller water path. Advantages: they are very cheap and will work on very low-pressure systems where other types will not work at all. They are the best emitters for very low pressure systems, such as gravity flow drip systems fed by water from rain barrels. Disadvantages: They clog up easily, especially if the water is hard with lots of minerals in it. They have poor water distribution uniformity compared to other types of emitter. They work good on small systems, where cost is a critical issue and uniformity of water distribution is not critical. By far the most common of these short-path emitters is a very inexpensive generic emitter called a “flag emitter” or a “take-apart emitter”. This emitter is made under numerous brands and names. It is easily recognized by the little flag shaped handle on it, you can disassemble it by twisting and pulling on the flag. The photo below shows two flag emitters, the one on the right is disassembled. You can see spirals that form the short, narrow water path on the male part of the disassembled emitter.
Tortuous-Path or Turbulent-Flow Emitters
The next type of emitters are called tortuous-path and/or turbulent-flow emitters. These emitters work by running the water through a path similar to the long path type, but the path has all kinds of sharp turns and obstacles in it. These turns and obstacles result in turbulence in the water, which reduces the flow and pressure. By using the tortuous path the emitter water passages can have a shorter length and larger diameter. These larger passages make the emitter less likely to clog up. I like tortuous-path and turbulent-flow emitters because they are simple, cheap, and work good.
Vortex emitters run the water through a vortex (whirlpool) to reduce the flow and pressure. If you reflect back on the high school lessons you slogged through, you will remember that the faster your car goes, the more likely you are to have a girlfriend. Wait, that’s the wrong high school lesson! The lesson we want is the lesson about the whirlpool around the bathtub drain. (A great visual image of the social life of that high school male with the slow car!) In the bathtub drain lesson we learned that the pressure drops at the center of a vortex. The vortex emitter uses that same principle by swirling the water around the outlet hole to cause a drop in pressure and a lower flow through the hole. Most vortex emitters also have very small inlet and outlet holes. I honestly think the small holes have more to do with reducing the flow than the vortex, but that’s just my opinion. Advantages– vortex emitters are small in size (about the size of a large pea) and very inexpensive! Disadvantage- because of those small holes they clog up easily, especially if you have hard water (ie; lots of minerals in the water.)
Yes, since some of you are wondering, I had a slow car in high school. My mother named it Leaping Lena because it backfired a lot. Wow, I really wish I still had my old 1950 Plymouth DeLuxe!
Diaphragm emitters all use some type of flexible diaphragm to reduce the flow and pressure. They use many different ways to do this, some have diaphragms with holes that stretch, others move the diaphragms back and forth to reduce the size of the adjacent water passages. The bottom line is they all use some type of flexible part that moves or stretches to restrict or increase the water flow. As with anything that moves, they will wear out eventually (which may be a very long time!) which is the downside. The advantage is that they tend to be much more accurate in controlling the flow and pressure than the previous types.
Adjustable Flow Emitters
Adjustable flow emitters have an adjustable flow rate. Typically the emitter has a dial that you turn to change the flow rate. The design of most of these is very similar to the short path type of emitter. Adjustable flow emitters tend to vary greatly in flow and have little pressure compensation. I recommend adjustable flow emitters only for use in pots and hanging baskets. Because the water needs of each pot or basket tend to vary greatly, the ability to adjust the emitter flow is very useful in these situations. Adjustable flow emitters often allow much higher flows which can be useful if you only need a few emitters on a valve circuit.
There is one last type of emitter that I am aware of, which is the mechanical emitter. The mechanical emitter uses a chamber which fills with water then dumps it out at preset intervals of time. Much like filling a cup with water and then pouring it out. I haven’t seen a mechanical emitter in years. The last one I saw was a prototype at Cal Poly, Pomona University back when I was a student there in the mid 1970’s. While extremely accurate in flow, they were too complicated and costly to produce.
Dripline, dripperline and other variations on that name are used to describe a drip tube with factory preinstalled emitters on it. Often the emitters are actually molded inside the tubing and all that is visible on the outside is a hole for the water to come out. The emitters are typically the tortuous-path or diaphragm type, but may be other types as well. The emitters are uniformly spaced along the tube, often several different spacing options are available. The primary advantage of dripline is ease of installation due to the preinstalled emitters. It is often used in agriculture, it also works well in situations where you want to create a solid band of watered soil, such as watering groundcover beds, vegetable gardens, and lawn.
Pressure Compensating vs. Non-pressure Compensating Emitters
There are two basic categories of drip emitters, pressure compensating and non-pressure compensating. These names are a little misleading, as all emitters are pressure compensating to some degree, that is essentially the purpose of an emitter! What this means is you can’t determine what is pressure compensating by the manufacturer’s literature, almost all of them can make that claim. Water pressure is measured in bars (yes kids, that’s metric) and most are designed to work best at 1,5 to 2,0 bars of pressure. For those of you in the good ol’ United States of America, that’s around 20 PSI (pounds per square inch, the water pressure measurement unit used in the USA.)
I’m going to define pressure compensating emitters as those that are designed to discharge water at a very uniform rate under a very wide range of water pressures. For the purposes of these guidelines I am going to say true pressure compensating emitters give essentially the same flow at 3,0 bars (45 PSI) as they do at 1,0 bars (15 PSI). As far as I know, all of the emitters currently being sold that fit this requirement are diaphragm-type emitters. But there may be exceptions, there are literally hundreds of different emitter designs on the market!
How do you know which emitters are pressure compensating and which aren’t?
Well, you can’t rely on label names or product names. As previously mentioned, all emitters can qualify to some degree as pressure compensating and it is common for emitters that don’t meet my requirements to be labeled on the package as “pressure compensating”. The best way to tell is to find the performance data for the emitter you are looking at. Is the flow rate pretty much the same at 1,0 bars (15 PSI) as it is at 3,0 bars (45 PSI)? If so, then it meets my requirements. Another way to tell is by the type of emitter. If it does NOT have a rubber diaphragm in it, then it probably does not meet my requirements to be considered pressure compensating. In many cases the only way to find this out is to buy one and carefully cut it open. I suggest putting the emitter in a vise and using a hacksaw to cut it in half. They are small, hard to hold, and made of hard plastic that is difficult to cut with a knife.
Should you use a pressure compensating emitter?
Surprise! You probably do NOT need pressure compensating emitters! Pressure compensating emitters that meet my requirements are typically more expensive than non-compensating emitters. So why spend the money on them if it is not necessary? For most residential applications the non-pressure compensating turbulent-flow type emitters are a good choice. You should use pressure compensating emitters if you have an elevation difference of over 1,5 meters (5 feet) in the area you are irrigating. So if you have a small hill in your backyard and you are going to install a drip system on it you should use pressure compensating emitters. Also you should use pressure compensating emitters if you plan on stretching the limits of your design, such as using a longer drip tube than is recommended in the drip guidelines on this website. While I don’t recommend stretching the design limits, a pressure compensating emitter will be more forgiving of such things. Unsure? Most of the time it will not hurt anything (other than your pocketbook) to use pressure compensating emitters. The exception is that most pressure compensating emitters should NOT be used with very low water pressure systems, such as gravity flow systems, as they often do not work at all with very low water pressure. See the Gravity Flow Drip Systems page for more suggestions for low water pressure systems.
Emitters come in a variety of different flow rates. The most common flow rates are:
2,0 liters/hour – 1/2 gallon per hour
4,0 liters/hour – 1 gallon per hour
8,0 liters/hour – 2 gallons per hour
I prefer a lower flow rate for most situations and I primarily use 2,0 l/hr (1/2 gph) emitters on my drip systems. Using this lower flow means I can install almost twice as many emitters on the same pipe and valve circuit! Plus, I save even more water because the lower flow emitters are more efficient! Most soils can’t absorb the higher flow rates, so the extra water tends to puddle around the emitter where it evaporates, or it may even run off into the gutter. With drip irrigation you want the water to be immediately absorbed into the soil as it comes out of the emitter. If you can find them I recommend 2,0 l/hr (0.5 gph) emitters. These are often called “1/2 gallon per hour emitters” in the USA. If you can’t find them, then use the 4,0 l/hr (1 gph) emitters.
If the soil is sandy I suggest you use emitters with a flow rate of 4,0 liters/hour (1 gph) or higher. In sandy soils the water tends to just go straight down in the soil, using a higher flow rate will force it to move sideways farther.
There are situations where a higher flow emitter is a better source. Are you planning to use automatic electric solenoid valves? If you have a very small drip system that will require only a few emitters you may want to use higher flow emitters. This is because the standard electric sprinkler valves often do not work at very low flows. Some valves will work at lower flows than others, so compare brands. Here are some general guidelines for keeping the flow within a range that most automatic (electric solenoid type) irrigation valves can handle:
0-50 emitters – find a low flow valve
50-100 emitters = 8,0 l/hr (2 gph)
100-200 emitters = 4,0 l/hr (1 gph)
200+ emitters = 2,0 l/hr (1/2 gph)
Remember, one trick for increasing the number of emitters on your system is to use more than 1 emitter per plant. Manual operated valves will work at any flow so you can use as little as 1 emitter with them. Mechanical motor-driven valves will also work for extremely low flows. However they are expensive and hard to find.
Mixing emitter flow rates
Mixing different emitter flow rates together on the same system is not a good idea. Pick a single flow rate and stick to it. Plants that need more water should have more emitters per plant, do not use emitters with higher flow rates on them. An exception is with potted plants, where different size pots and types of soil in the pots make using adjustable flow emitters the best choice.
To install the emitters you create a hole in the drip tubing using a punch. Then you press the barbed emitter inlet into the hole and the barb locks it in place. Because the poly drip tube is elastic, it stretches around the barb and then seals itself around the stem of the barb. The key is that you don’t want the hole you punch in the tubing to be bigger than the diameter of the barb stem. When the hole is larger than the barb stem, the hole won’t seal and you will have a leak. If the emitter manufacturer makes a special punch I suggest you use it as it will create the proper size hole in the tube. If a special hole punch is not available, in most cases an ice pick or even a nail will make a sufficient hole. Just make sure the diameter of the punch is not bigger than the stem on the emitter barb. Be careful to punch the hole through one side of the tube only, it is easy to go all the way through one side of the tube and out the other.
I suggest you buy some goof plugs before you start. Goof plugs are small plastic barbed plugs used to fill the holes that get punched in the wrong place. If you install an emitter in a place you don’t want it, simply pull it back out and install a goof plug in the hole. If you try to put the emitter back in the same hole it will probably leak. Once you have a goof plug installed in the tube don’t pull it out! If you want to reinstall the emitter make a new hole in the tube. The goof plug has a larger barb and stem than most emitters, which is how it fills the old stretched-out holes without leaking. When you pull out a goof plug the barb is so large that often it rips the tubing and ruins it. The only cure then is to cut out a section of tubing and splice in a new piece of tube using two tubing couplings.
Some emitters are made to be self-piercing of the tube and do not require the use of a punch. Generally this feature requires a special tool to be practical and is very difficult to do with just your hands. These installation tools are often pretty fancy and work similar to staple guns to install multiple emitters loaded into a cartridge. The tools are usually only sold at specialty irrigation stores. You can punch a hole for the self-piercing barbs with a standard hand-punch if you don’t have the special tool and are having trouble pushing the self-piercing barbs into the tubing.
Brand & Model Selection:
There are a lot of different brands and models of emitters! If you are unsure of a model, the best thing to do is to buy a sample or two, a short length of hose, and a hose bib adapter and test them by hooking them up to a faucet. To be real honest, for residential use most emitters I have tested seem to work pretty good. You can make some pretty good decisions about which is best for you by simply looking at them closely and considering your specific needs. Consider the following points.
Do you have hard water? Mineral deposits from hard water can plug emitters with small openings, such as vortex type and short path type (that’s why both those types are often made so they can be disassembled for cleaning.) Look for bigger passages if you have hard water. Remember that the opening you can see when you look at an emitter is almost always large, manufacturer’s tend to hide the smaller diameter ones inside the body where you can’t see it!
Take a close look at the emitter’s water inlet hole located on the barb. What shape is it? A round hole is easily clogged by a grain of sand in the water. An oblong (-) or cross (+) shaped hole is much more resistant to clogging. Some emitters even have multiple inlet holes of different and odd shapes. Multiple holes and odd shaped holes make it much less likely the inlet will become clogged by a grain of sand or other trash in the water! These are signs of a good quality emitter. The shape of the water exit hole is not nearly as critical to quality.
Consider ease of installation. If you are going to use the type of emitters you install on the tubing yourself take a look at the shape of the emitter. Put your thumb on it and press hard, as if you are pressing the barb into a hole in the tubing. Does it hurt your thumb? Your fingers can get really sore after inserting a few dozen emitters into the tubes. Some emitters have flat surfaces to press on, others don’t. It can make a big difference in how uncomfortable it is to install the emitters. At the end of the day when your thumb is bright red and feels like it has been pounded on with a hammer, you may wish you had spend a little more money to buy an easier to install emitter! Regardless of the emitter you choose I suggest wearing a heavy glove on the hand you use to press the emitters into the tube.
Some models and brands of emitters spit a small stream of water out of them each time the water is turned on. Vortex type and diaphragm type emitters most often tend to spit. Spitting doesn’t particularly hurt the emitter performance, but it can be a problem if there are people around. some emitters can spit the water over a distance of two meters! (Translation to English units: “far enough to cause an embarrassing moment when you have that special guest sipping afternoon tea with you on the patio!”) If spitting might cause a problem in your yard, I suggest getting a few test emitters and trying them out to see if they spit. The staff at an irrigation specialty store can probably tell you which brands spit. Don’t expect the folks at the local hardware/home store to be able to tell you which models spit. I am aware of that some people have installed these intentionally in locations where they will spit of people! However, more often they just install a small tube without an emitter. The installation of spitting tubes as jokes in gardens are nothing new, they are found in ancient gardens in Europe.
OK, let’s get this out up front; I do not like multi-outlet emitters. There are a lot of people in the irrigation industry that disagree with me on this topic (as well as a lot who agree with me), so be aware that the following is just an opinion based on my experience. You can take it, or leave it, no hurt feelings on my part. The problem with multi-outlet emitters is that they require the use of small tubes to route the water from the emitter to the plants. These small tubes are typically called distribution tubes or spaghetti tubes. The tubes are about 6mm diameter (1/4 inch) and made of polyethylene or sometimes soft vinyl. This tubing is extremely high maintenance. It breaks, it gets cut by garden tools, it gets kicked around. It pulls loose from the emitter. Bugs crawl into it and get stuck. Pets and wildlife chew on it. It’s trouble, plain and simple. Trouble, trouble, trouble! I suggest that you will be much happier if you avoid this small tube. I suggest you snake the larger 15mm (1/2″) tubing between your plants and use single outlet emitters on it. The larger diameter tube holds up much better. One exception; the small tubing works good on trellises and for hanging pots where the tube can be firmly attached to a wood or wire supports for protection.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Here are some spreadsheets I have created to help you calculate the capacity and water pressure loss through pipes and tubes of various types and sizes. These should be useful for both figuring pressure loss in mainlines and laterals. Each spreadsheet allows for multiple sections of pipe of various sizes and flows. All you do is select the proper spreadsheet for the type of pipe you are going to use, select the pipe size from a drop down list, enter the flow through the pipe in GPM, then enter the length of the pipe in feet. The spreadsheet calculator will then do the math to give you the water velocity in the pipe along with the pressure loss in PSI for that section of pipe. If there are multiple sections of pipe the spreadsheet will also total all of them for the total pressure loss.
Full instructions for using the spreadsheets are included on the spreadsheets.
Please read this paragraph before you try to use the spreadsheets.
These spreadsheets use Apache Open Office. That means you need to have the Open Office program installed on your computer for them to work. I use Open Office because it is a free, safe program that is available for just about every desktop and laptop computer make and model. That means just about everyone can use it, and nobody has to make a major software investment just to use the spreadsheets. If you don’t already have Open Office you will need to install it on your computer before you can use the spreadsheets. You can uninstall it when you are done using it if you want. Download it free from http://www.openoffice.org . It does take a while to download Open Office. It is a full office productivity suite. (Check it out, there are some cool apps in it!)
Your browser may try to “open” the spreadsheets if you left click on the links, even if you don’t have Open Office installed. This is because most computers have some type of minimal spreadsheet reader installed on them, so the reader will try to open these spreadsheets. If they were just simple spreadsheets they would probably work with the readers. But they aren’t. In most cases you will get a corrupted version of the spreadsheet that does not work. This is because these friction loss calculators use very complex formulas that the “stripped down” spreadsheet readers can’t handle. You need to install Open Office. I may have already mentioned this. 🙂
Remember, you can un-install Open Office when you are done if you don’t like it.
If you try to open the spreadsheets directly using your Internet browser they will probably open as Read Only and the spreadsheet won’t work. This is because the browser will not open an executable file directly. (It is trying to protect you from possible viruses.)
Solution: Right click on the link and “Save” the file to your hard drive. The actual wording varies, so depending on your browser you may select “Save link as..”, “Save Target as…”, etc. This should save the spreadsheet file to your hard drive. Then open it directly from your computer without using the browser plug-in. Tablet and phone users: you may need to get to a real computer to use the spreadsheets.
If the spreadsheets don’t work for you..
Do you have Open Office installed? If not, install it.
Are you using Open Office to read the spreadsheet? Sometimes another spreadsheet program will try to open it instead of Open Office.
Have you tried saving the spreadsheet file to your desktop, starting up Open Office, then opening the spreadsheet with Open Office?
If the spreadsheet says it is “Read Only” you probably are using a non-compatible plug in. Install & use Open Office.
Just dragging the spreadsheet link to your desktop may not actually save the file. You need to right click on the link and select Save as…
If you have an older version of Open Office you may need to upgrade it.
Try rebooting. I’ve experienced a problem where if I try to open one of these spreadsheets in a browser the computer gets messed up and won’t start Open Office. Rebooting fixed the issue.
SPREADSHEET CALCULATORS FOR PVC PIPE
Do not try to open these spreadsheets by left clicking on the links. Save the spreadsheets to your hard-drive first. See the explanation above.
Q. 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.
Q: The pressure is blowing off the pipes/tubes from the barbed fittings on my drip irrigation system. This is only happening on hot days (30°C=86°F in the shade). Pipe temperature could be as high as 45°C=113°F. Our water pressure varies between 2.5 and 3.1 bar (35 and 45 PSI.)
A: Drip tube should not blow off the barbs, even on a hot day when the temperature softens the plastic tubing (however the heat does make it easier for them to blow off!) There are three common reasons the tubes blow off.
1. The most common problem is that the water pressure is too high. This is probably your problem. The water pressure should be around 1.3 to 2.0 bars (20 – 30 PSI). You should install a pressure reducer after your valve to lower the pressure.
2. The pipe and fittings may not be the same size. This is one of the pitfalls I warn about in my Drip Guidelines. 16mm and 18mm tube are both commonly referred to as 1/2 inch in the USA! The fittings for these two are not interchangeable.
3. Pressure spikes can pass through the less expensive pressure reducers often sold for drip systems. If you have high water pressure this may be the problem. The solution is to install a high quality brass pressure reducer valves. These generally are sold in the plumbing department rather than the irrigation department of stores and cost $50.00 or more.
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.
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