Irrigation Tutorials

Questions about Sprinkler and Drip Irrigation? Free tutorials, articles, FAQs, and reviews. You've found the web's mother lode of irrigation information!

Posts Tagged ‘drip irrigation’

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

Tuesday, June 3rd, 2014
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, click here.

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- click here.

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. Click here 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 click here.

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.

Drip Irrigation Design Guidelines – Basics of Measurements, Parts, and more

Tuesday, June 3rd, 2014

Index to the Guidelines:

If you wish to print out the entire Drip Guidelines Package for reading off-line, print this page and each of the ones listed in the links above.

Background:

Drip irrigation is the most efficient method of irrigating. While sprinkler systems are around 75-85% efficient, drip systems typically are 90% or higher. What that means is much less wasted water! For this reason drip is the preferred method of irrigation in the desert regions of the United States. But drip irrigation has other benefits which make it useful almost anywhere. It is easy to install, easy to design, can be very inexpensive, and can reduce disease problems associated with high levels of moisture on some plants. If you want to grow a rain forest however, drip irrigation will work but might not be the best choice!

Drip irrigation (sometimes called trickle irrigation) works by applying water slowly, directly to the soil, bloop, bleep, bloop, bleep. The high efficiency of drip irrigation results from two primary factors. The first is that the water soaks into the soil before it can evaporate or run off. The second is that the water is only applied where it is needed, (at the plant’s roots) rather than sprayed everywhere. While drip systems are simple and pretty forgiving of errors in design and installation, there are some guidelines that if followed, will make for a much better drip system. The purpose of this tutorial is to guide you toward materials and methods that will increase the benefits of your new drip system, while steering you away from some common misconceptions and practices that can cause you trouble.

“What’s with the Metric measurements? !!” Come on, quit whining, the rest of the world uses metric without problems!!! OK, don’t flame me, I give up, I’ll compromise… While a lot of drip irrigation research has occurred in the USA, most of the credit for making drip irrigation what it is today really should go to Israel and South Africa. So I’m going to honor that contribution by using the metric system as the primary measurement units for these guidelines. After all, metric is really the “native” measurements of drip irrigation. When I started using drip irrigation (back in the dark ages of irrigation) all drip data and products were in metric! But because I’m such a nice guy (inflated ego alert!! Dump some ice water on this guy!), I will provide English measurements also. So don’t panic.

This tutorial is setup in a multilevel format. Each of the guidelines below describes a basic rule for drip irrigation design, the guidelines follow in the logical order for creating a design. You can think of the guidelines as design steps if it helps. This page is the top level, here you will find a brief description of each design guideline. For many of the guideline topics there is a link to another page with expanded information on the guideline topic. There may be additional links from there to allow you to dig even deeper into the drip irrigation knowledge base. So you choose how much you want (or need) to learn. My recommendation is that if you want to print out something, print this page. Then refer to the other levels (and print them if necessary) as needed. That will save you a lot of unnecessary wear and tear on your printer. It might also save a tree from going to the paper mill!

Parts of a Drip system:

If you don’t know a lateral from a pressure regulator start by learning about the basic parts of a typical drip irrigation system. I strongly suggest that even if you are familiar with drip irrigation you start be reading through The Basic Parts of a Drip System page now. It contains a lot of tips and recommendations.

A simple drip system.

Illustration of a very simple drip system.

Complex home drip system

A more complex home drip system.

Suggestion: Click on the image above for a pdf version of the drawing that prints better.

Prescriptive Drip Design Guidelines:

These guidelines will provide you with all the information necessary to design a residential drip system for a typical yard. These guidelines are what is termed a “prescriptive standard” in the building industry. A prescriptive standard is a set of rules and/or methods that, when followed, allow you to skip the engineering calculations for a design. Obviously this saves a lot of time and effort in preparing a design. The downside to a prescriptive standard design is that it tends to “over-design” in order to make the design “one size fits all”. Unlike sprinkler irrigation, drip irrigation systems are much more forgiving of design error, the cost of over sizing the materials is minimal, and so a prescriptive design method works very well for almost everyone. To prepare a fully engineered drip irrigation design requires a massive number of difficult mathematical calculations. If there was ever a great place to use prescriptive standards for the design, it is drip irrigation!

Emitter Type and Flow:

Use pressure compensating emitters if you have an elevation difference of over 1,5 meters (5 feet) in the area you are irrigating. For more level areas turbulent flow emitters will work great and are often less expensive. For gravity flow systems use short-path emitters, they typically work better than the others at very low water pressures.

For most soil types 2,0 l/hr (0.6 gph) emitters work well and are more economical. For sandy soil use 4,0 l/hr (1 gph) emitters.

For more information see Drip Irrigation Emitters.

How Many Emitters are Needed?

1 or 2 emitters per plant, depending on the size of the plant. Trees and large shrubs may need more. Obviously, using two allows for a backup if one clogs up (which happens now and then, even on the best designed and maintained drip systems.) But just as important, more emitters also wet more soil area. This results in more roots, and a healthier, happier plant. Exception: if the plants are very close together you may need to use less than 2 per plant in order to maintain the minimum spacing between emitters. Minimum spacing for emitters: In most situations install emitters at least 450mm (18″) apart. A good default spacing for quick and dirty design is to space the emitters 600mm (24″) apart. For supplemental watering of low-water-use plants, use one emitter per plant. Supplemental watering is used for establishment of drought tolerant plants that are not likely to need irrigation once they have developed a good root system, or might be used to apply a little extra water now and then to make them a bit more lush. Use of low-water plants with supplemental drip irrigation is considered very “green” and is the current trend in landscape design.

Rule of thumb- install emitters 600mm (24″) apart under 80% of the leaf canopy of the plant. That’s where the roots are, and the roots need water. If the soil is very permeable install emitters 300mm to 450mm (12-18 inches) apart. For more information and a better method of determining spacing see Drip Emitter Spacing.

Backflow Preventer:

Drip emitters rest directly on the soil so it is especially important to have a backflow preventer to prevent water contamination by soil-borne disease. There are several types that will work depending on your situation and local codes. For more information see Irrigation Backflow Preventers.

What valve type and size to use:

Use a 20mm (3/4″) valve for most systems. Any type of valve may be used. For more information see Drip Irrigation Valves.

How many emitters per valve?

Use the charts below to determine how many emitters to install on each valve circuit. If you don’t know what size your water supply pipe is, see How to Find the Size of a Pipe.

Emitter volume used Any water supply that comes out of a building, such as a hose bib. Any system with a pump*. 20mm (3/4″) water supply. Use a 20mm (3/4″) valve. 25mm (1″) water supply. OK to use a 20mm (3/4″) valve.
2,0 l/hr (0.6 gph) 300 300 700
4,0 l/hr (1 gph) 180 180 420

*Pumps can be tricky. This is a conservative figure in order to make it work with the majority of pump fed systems. You may be able to use a larger number of emitters by calculating the actual output of your pump. See the Irrigation Pumping Systems tutorial for more information about using pumps.

Water supplies coming out of a building are also a problem. The piping in buildings is almost never designed to carry large amounts of water such as is used by irrigation systems. To be safe I assume you have significant restrictions. 95% of buildings have these restrictions so don’t increase the flow unless you really know what you’re doing. Increasing the flow could cause extreme damage to the plumbing in the building!

 

 

Mainlines & Laterals.

Use 25mm (1 inch) PVC, PEX or polyethylene irrigation pipe for mainlines (“mains”) and laterals. The total length of the mainline and the lateral together should not be more than 120 meters (400 feet). So you could have 100 meters of mainline and 20 meters of lateral, for a total of 120 meters of both. But you should not have 80 meters of mainline and 60 meters of lateral because the total of both would be more than 120 meters. Remember mainline is the pipe before the control valve, lateral is pipe after the control valve. Many drip systems won’t need mainlines or laterals. Or they may need just a mainline, or just a lateral. For more information see the sections on mainlines and laterals in the The Basic Parts of a Drip System.

Maximum drip tube length.

The length of drip tube (or drip hose) may not exceed 60 meters (200′) from the point the water enters the tube to the end of the tube. Thus you could have 120 meters (400′) of tube if the water entered the tube in the middle (that would be 60 meters from the point the water enters the tube to the end of the tube in each direction, which would be OK). You can extend one tube off of another as long as the total length of the tubes that are connected is not more than 60 meters (200′). For more information see the drip tube section of The Basic Parts of a Drip System.

Buried Emitters

Never bury emitters underground unless they are made to be buried. If you bury the emitter roots will grow into it and clog it. If you do want to bury the emitters do a search for “subsurface drip irrigation” to find specialty drip products designed to be buried. Follow the manufacturer’s recommendations for those products as they must be designed and installed to very exacting standards to avoid problems.

Buried Tube.

Don’t bury the drip tube. If you do bury drip tube don’t complain to me if gophers, moles or other rodents chew it up. I’ve seen them gnaw to pieces a buried drip system over night. One day it works, the next, it’s garbage. It only takes one gopher (or mole, squirrel, etc.), and one evening! You’ve been warned! Other wildlife (and most dogs), will also chew the tubes. It helps if you provide a water source for them to drink from if possible. A water bowl with an emitter over it to keep it full sometimes will distract wildlife from the tubes. You may need to train your dog not to chew the tubes, dogs seem to chew on the tubes for no real reason other than to annoy you. If you want to hide the tube, dig a shallow trench for it, so that it is just below the level of the surrounding soil. Don’t put dirt over the tube. Throw some mulch or bark over the top to hide the tube, or plant a low spreading plant that will grow over it and hide it.

Feeder, Spaghetti, and Distribution Tubing

Avoid using feeder, spaghetti, or distribution tubing if possible. For more on this topic see the section on spaghetti tubing on The Basic Parts of a Drip System page.

Hard-Piped Drip Systems

A type of drip system used in commercial and high quality landscapes called “hard-piped” uses buried PVC pipe rather than poly drip tubing. The PVC pipe is installed underground and a pipe goes to each plant location, so it takes a lot of pipe. At each plant the emitters are installed above ground on short poly tubes called “risers”. Hard pipe systems can be pretty expensive due. For a detail drawing of this click here. The design of a hard-piped drip system is essentially the same as shown here, except you would use PVC or larger size poly irrigation pipe in place of the inexpensive drip tubing.

Fittings- Use the correct size!

This is really important! There are many different sizes of drip tubing sold, and the fittings have to be made for the exact size tube you are using! If they aren’t, they will either be very hard to install, or the tube will blow off the fitting. Sometimes it takes a week or so for the tube to come loose, but if the fitting is even 1mm too large, the tubing will come off eventually. Never heat the drip tube or use oil on it to make it easier to insert into or onto the fittings. See the section on drip tube in The Basic Parts of a Drip System for more information on fittings and tips and tricks for installing fittings.

Stake down the Drip Tubes!

Stake the drip tubes to the ground once every meter (about 3 feet). This keeps the tubes from wandering. No kidding, they tend to move around by themselves! Staking them also helps protect them from damage. I prefer to use metal stakes as the plastic ones I’ve tried pull loose too easily. Wire that rusts holds even better, as the rust binds the wire to the soil. After a few days they can be almost impossible to remove. They will rust away in a few years, but by then the tubing has adapted to its position and stays in place pretty well. Standard 12 gauge wire works well, as does pieces of wire coat-hangers. Buy some coat-hangers at a yard sale or thrift store and help recycle! Bend a 300mm (12 inch) length of wire into a”U” shape to make a tubing “staple”. Or you can buy metal staples that are made for holding down erosion control blankets, they work great.

Check Valves, Slopes, Hillsides:

Install check valves if the drip system is on a hillside of slope to prevent the water in the tubes from draining out through the lowest emitter each time the system stops running. For more information see the drip tube section of The Basic Parts of a Drip System.

Air Vents:

Install an air vent at the highest point on each drip valve circuit. If there are multiple high points you an air vent installed at each one. Air vents should always be used for drip systems on sloped areas. Air vents are often not installed on small homeowner drip systems without any slopes. If air vents are not used be sure the emitters at the highest points are not installed where dirt could be sucked into them. For more information see Drip Systems for Slopes and Hillsides.

Flush Valves and End Caps

Install a flush valve or end cap at the end of each drip tube. Automatic flush valves are available, however my personal preference is for manual flush valves. See the section on flush valves in The Basic Parts of a Drip System for more information.

Patios with Potted Plants and Trellises:

You will probably want 6mm (1/4″) feeder/spaghetti/distribution tube running to the plants if they are in pots just to make it less obtrusive visually. Try to use as little 6mm (1/4″) distribution tube as possible, keep the tube lengths short as much as possible, and only put 2 emitters on a single 6mm (1/4″) tube. If a 6mm (1/4″) tube is longer than 5 feet, use only one emitter on it. I like to staple the tubes to something to keep them in place if possible (like stapling the tube to a trellis for hanging plants.) Use a wire stake to hold the emitter in place in a pot. Don’t pull any of your tubes tight, snake them a little, leaving some slack in them to allow movement. The tubes will expand and contract with temperature changes, you don’t want them to tear or pop the fittings off.

So for example, I run standard 15-16-17mm (1/2″) tube along the patio perimeters, trying to put it in places it will be out of the way or I can hide it. I also run it up onto the trellis if there are lots of hanging plants, putting it on the back side out of view and clamping it to the trellis using standard conduit or pipe clamps. (I’ve found conduit clamps are cheapest, look in the electrical dept at any hardware store.) From the 15-16-17mm (1/2″) tube I run short lengths of 6mm (1/4″) tube to the potted plants. Remember: more 6mm (1/4″) tube = more problems.

Backflow preventers are always an issue if you have hanging plants and trellises. Vacuum breaker or anti-siphon type of backflow preventers must be installed above the trellis or they won’t work. Both those types of backflow devices must be installed at least 150mm (6″) higher in elevation than any of your emitters. This is generally not very practical to do. I have seen people run copper pipe up a trellis and put an anti-siphon valve 150mm (6″) above the trellis. But in most cases you need to use a double check, or preferably a reduced pressure type of backflow preventer. Those can be installed at any elevation (a reduced pressure type should be above ground.) I recommend a reduced pressure type. See the backflow preventer page for more detailed information.

Beyond these issues, the other basic drip guidelines in this tutorial all apply to patio and trellis drip systems.

Gravity Flow Systems:

If you are using a gravity flow water source like a rain barrel see the suggestions on the Gravity Flow Drip Systems page.

Drip System Sample Detail Drawings:

I have put together a few sample drawings of drip system parts and assemblies that you might find useful. See Drip System Sample Detail Drawings.

Now it’s time to get to work! Don’t forget to read the Irrigation Installation Tutorial. It covers a lot of tips and tools for installing your drip system!

 


Technical Data:

This is just for those who want to know all the little details. Everyone else can ignore this information. Here are the assumed pressure losses for the prescriptive drip system design used in these guidelines:

  • Valve 0,4 bars
  • Backflow Preventer 0,8 bars
  • Pressure Regulator 0,0 bars
  • Filter 0,2 bars
  • Mainline & lateral 0,4 bars
  • Drip Tube 0,2 bars
  • Emitters 1,0 bars

Total Pressure required 3,0 bars (44 PSI)

Based on 0,2 l/s flow for 20 mm valve with smaller supply, 0,4 l/s flow for 20 mm valve, and 0,9 l/s for 25 mm valve.

Watering a very narrow 30″ wide lawn strip

Saturday, March 9th, 2013

Q. I need to water a 2.5′ wide by 21′ long grass strip in the middle of my driveway. What is a good method for this narrow an area? My home is located in Southern California.

A. Irrigating lawn in areas less than 4′ wide is very hard and results in a lot of wasted water. It is illegal to install a grass area less than 4 to 6 feet wide in many cities, especially in California and other western States, including ALL of Arizona and most of Nevada (the minimum width varies from town to town.) Enforcement is typically limited to new development, but if you get a permit from the city for the work you may get nailed on this issue.

Using Sprinklers

If you do use sprinklers there is going to be a lot of water waste from over-spray onto the concrete. It will likely run down your driveway and when (not if) the next big drought cycle hits and they start with the “water police” thing you will likely have to stop watering your strip or risk a “fix it” ticket.

If you do use sprinklers you will reduce the radius of each sprinkler to your 30″ width and then you reduce the distance between sprinklers by a similar %. I recommend using side-strip sprays rather than the center-strip type as you will have a lot less over-spray on to the concrete with them. The side strip side are installed down both sides of the strip. Center spray types are installed down the center of the strip. Using center strips type will require half as many sprinklers, but the cost of this initial savings is lousy performance, poor efficiency, and lots of wasted water (it is common when using center strips that 50% or more of the water applied will be wasted.) So let’s say you decide to use 4′ x 12′ pattern side-strip spray nozzles in 4″ pop-up bodies. Since your area is only 30″ wide you would need to reduce the spray width from 48″ to 30″. That would be 62% of 48″ ( 30″ / 48″ = 0.625). So you would also need to reduce the 12′ distance down to 62% also, which is 7.5′ (12′ x 0.62 = 7.44′). So in your 30″ x 21′ area you would space the heads 7′ apart on both sides. After installing the system you would reduce the radius of each head as best you can using the radius reduction screw. It is unlikely you will be able to avoid some over-spray onto the walk as noted earlier. If you decide to use center strip nozzles the procedure and spacing would be the same, there would only be one row of heads, however, installed right down the center of the strip. With center strips you will have to allow more water to overspray onto the cement driveway, if you don’t you will get dry yellow edges. If you want a better explanation of why see this page on sprinkler spacing.

Using Subsurface Drip

Your other option is to use subsurface drip. This is what I would do. In this case I would use three drip tubes running the length of the grass strip. Place one down the middle and the other two should be 4″ in from the edge of the driveway concrete on each side. Use dripperline with 1 gph emitters spaced 12″ apart. Netafim, Rainbird, and Toro all make subsurface dripperline. Make sure the dripperline is a model that the manufacturer claims in their literature is for subsurface installation. Subsurface dripperline uses a different type of emitter designed to keep out dirt and roots. Read my drip guidelines for info on filters and pressure regulators you will need. The salesperson at the irrigation store may tell you that you only need two tubes, which normally would be correct, they typically are spaced 18″ apart, not 12″. There are a couple of reasons I am suggesting 3 tubes rather than 2. First is to get the total flow up because the area is so small and most automatic solenoid valves don’t work very good at really low flows. Another reason is that the concrete on both sides absorbs and radiates a lot of heat, and this is going to make your little lawn strip dry out fast. That’s also why I suggest the dripperlines at the edges of the area be 4″ from the concrete, otherwise the lawn edges right up against the concrete tend to dry up and turn yellow. You are going to need to be careful in selecting your valve, the dripperlines in your 21′ long area are so short that the total flow using 1gph emitters is only going to be 1 GPM; (3 tubes, 20′ long with 1gph emitters every foot. So 20′ x 3 tubes = 60′ of tube. 60′ of tube x 1gph/ft = 60 gph. 1 gpm = 60 gph.) A lot of automatic valves will not work at flows that low. Make sure the rated flow range in the literature for the valve goes that low.

To install your drip system remove the top 5″ of soil from your planter. Now till the soil another 4″ deep. Tamp down the soil to lightly compact it and get rid of air voids. A 8″x8″ hand tamper tool is good for this, you can buy one at any decent garden shop or home improvement store. Now place your dripperline tubes down on top of the soil and use steel erosion control staples to hold the tubes in place. Put a stake every 36″. You can buy the stakes at the irrigation store, they all carry them. The metal stakes work much better than the plastic ones made for drip tube. The stakes are very important, they will rust into the soil and hold the tubes in place. Without them the empty tubes will float to the surface during the winter when the soil becomes saturated during rain storms.

Now put down the final 3″ of soil over the top of the tubes, tamp it down and install your sod (which should be about 1″ thick and should bring the sod surface up even with the top of the concrete.) You will need to lightly hand water the sod for a week or two to keep it cool and moist. It needs time to grow roots down to where the subsurface water from the dripperline is. Slowly back off the hand watering after a couple of weeks. Watch the sod’s color to see how well it is rooting in. If the sod is still in need of top-watering by hand it will turn a dull “flat green” color. When you first install it, the sod will be that dull flat green color because it is stressed from the cutting,shipping and installation. It’s easier to see the color if you stand back and look at it from a distance. Right after you install the sod take a minute to look carefully at it and notice the stressed dull color. Then also note the brighter green color it changes to after you water it the first time it. Now you know what stressed sod looks like and what to look for over the next few weeks. If it is hot or the warm winds are blowing when you install the sod you may need to hand water it more often. Usually watering a couple of times a day is sufficient until the sod is established.

Pump Cycles On Briefly When Irrigation is Off

Thursday, November 1st, 2012

Q.  My irrigation pump runs fine when the system is operating, but after it turns off it cycles on for 5 seconds every 10 minutes or so.

A.  If you are using a pressure switch and pressure tank to turn the pump on and off my first guess would be that you have a water leak in your irrigation system.  The water leaks out, which cause the water pressure to drop, then the pump kicks on and recharges the pressure.  Then the pump shuts off again.  That would cause exactly this symptom.

Knowing the problem is the easy part.  Finding the leak, that could be harder to do.  It could be a zone valve that isn’t turning off all the way or it could be a leaky pipe.  You can narrow the search area a little,  the leak will be someplace in the pressurized part of the system, that is, between the pump and the zone control valves.  Start by looking for obvious dripping, then look for someplace that seems wetter than it should.  If it is a leaky zone valve then the water will be leaking through the valve into the sprinkler zone pipes and will dribble out at the lowest sprinkler head.  So look at the sprinkler heads.  There will be a small “swampy” area around the lowest sprinkler head that is controlled by that valve.

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

Thursday, February 3rd, 2011

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 http://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.



IrrigationTutorials.com

IrrigationTutorials.com

Custom Search



Ads (not endorsements):

 

wp