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Drip Irrigation Valves

by Jess Stryker

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

There are many different kinds of valves available. Most drip irrigation systems will need at least two different types; an emergency shut-off valve and a control valve.

Emergency Shut-Off Valve

An emergency shut-off valve should be installed at the closest point possible to your water source, that is, the location where you tap in for the irrigation system. Without this valve you will need to shut-off the water to the entire house if you have an irrigation breakdown and need to work on the mainline or irrigation valves. The most commonly used valves for this purpose are "gate valves" because they are inexpensive. Unfortunately the cheap gate valves you're likely to use also tend to wear out quickly and start leaking. While a gate valve will get you by, I recommend that you use a "ball valve", "disk valve", or "butterfly valve". These may cost a bit more (prices are becoming more reasonable as ball valves slowly are replacing gate valves for plumbing.) Ball valves are the least expensive of these and are much more reliable and will last several times longer than a gate valve. So if you pay twice as much for a ball valve it's probably still the best deal! If you do use a gate valve make sure that it is a good quality one. There's nothing worse than trying to work on a irrigation system when you can't shut off the water completely. For some very small drip systems an emergency shut-off valve is simply not cost effective. For example; a manually operated drip system where an existing faucet or hose bib is used to turn the system on and off.

 

Zone Control Valves

Zone Control valves are the valves that turn on and off the water to the drip tubes. Often these are automated valves that are turned on and off by a irrigation controller/timer. For a small drip system there may be only one zone control valve. Bigger systems may have several zone control valves, for example they may have one the turns on the water to the front yard, another for the side yard, one for the vegetable garden and a final one for the back yard. There are two basic styles of zone control valves to choose from. Take a look at the image below, descriptions follow.

Globe Valve, Anti-Siphon Valve
Glove Valve on left, Anti-Siphon Valve on Right

Standard Globe Valve:

Glove valves are available in just about any size. They are often installed underground in a box or vault. Since a globe valve doesn't incorporate a backflow preventer you must provide one separately. See the section on backflow preventers. The globe style valve is the most commonly used valve on large commercial drip systems.

Anti-Siphon Valve:

Available only in 20mm (3/4 inch) and 25mm (1 inch) sizes. This is my recommendation for most homeowners. The anti-siphon valve incorporates a backflow preventer into the valve. This saves a considerable amount of money, as backflow preventers are very expensive. The anti-siphon valve MUST be installed above ground and MUST be at least 150mm (6") higher than the highest drip emitter. This may prove a problem for some locations, since you would likely have to put the valves at the highest point in the yard. I have seen a anti-siphon valve installed on top of trellis in order to get it above the emitters for hanging baskets. On a slope the simplest solution is to run a mainline up the slope to the anti-siphon valve installed at the top of the slope. From there pipes run down to the emitters.

Indexing Valves (standard and anti-siphon):

Indexing valves are a single valve unit that controls several valve zones. The index valve has a water inlet and several water outlets. When the valve receives a signal from the control unit it opens the first water outlet, at the next signal it switches from the first to the second outlet. At each signal it switches to the next outlet until it gets back to the first outlet, at which point it shuts off. Indexing valves require a special controller to operate them. Indexing valves are usually available in models with or without a built in anti-siphon device. So an indexing valve may be also an anti-siphon valve. The anti-siphon indexing valve MUST be installed above ground and MUST be at least 150mm (6") higher than the highest drip emitter. Indexing valves have never been widely popular and are generally only available in localized regions where a nearby manufacturer has heavily promoted them. Perhaps the best know indexing valve is made by the K-Rain company, they are popular in Florida where K-Rain is located.

Operation Method:

The control valves may be manually operated or they can be remotely controlled. Manual control is simple, the valve has a handle you use to turn it on. Remote control valves are either electric or hydraulic, but almost everyone uses electric solenoid type valves. The valves are turned on and off by a timer called an "irrigation controller" or often just called a "controller". Anti-siphon, globe, and angle valves are all available as automatic valves. Most controllers and valves sold today are standardized, you don't need to use the same brand of controller and valve. The standard is a normally closed valve that uses 24 volt alternating current to actuate the valve. When 24 volts of current is applied to the valve solenoid wires the valve opens, when the voltage is turned off the valve slowly closes. This way the valve will close during a power failure or if a wire breaks. There are some exceptions to this standard operation method. To save power, controllers that run on batteries or solar power often use a special type of solenoid on the valves called a "latching solenoid". Latching solenoids work like a toggle switch, when a short burst of power is detected the valve switches open (if it was closed) or closed (if it was already open). Generally if latching solenoids are required there will be a warning and instructions on the controller. If the controller doesn't plug into a power source, chances are it uses latching solenoids. There are a few specialty controllers and valves that use their own proprietory system and are not compatible with either the standard or latching solenoids, but these are rare and seldom used by homeowners. The most common are Indexing Valves (see above). Another common one is a small solar-powered controller and custom valve solenoid combination sold under the brand name LEIT®. While a little beyond the budget of most homeowners, LEIT controllers can operate on very low levels of light, they claim moonlight is sufficient. (If you see something that looks like a parking meter installed in the middle of a landscaped road median island, you've spotted a LEIT controller. They are very popular with highway departments.)

 

Valve Body Materials:

Valves are available with either brass or plastic bodies. Most used today are plastic, but brass is still widely available and preferred by some pros, especially when high water pressure is present. There is no doubt that a brass valve will last longer if installed in the sunlight. From an operational point of view, both are reliable, especially for automatic systems. For manual valves my experience is that brass will last much longer. For automatic control valves I almost always use plastic, my experience is that when buried or protected from sunlight it holds up as well as brass and is less expensive. If you use plastic valves above ground you may wish to consider building a cover for them to protect them from sunlight, which can destroy the plastic over time. My experience is that even when made using UV resistant plastic, the plastic valves will start to break down after a few years in the sunlight.

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


 

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