There are three basic types of valves used in irrigation systems – gate valves, ball valves, and electric valves. Gate and ball valves are both manual valves that can be used if you do not plan to automate your irrigation system.
The gate valve has a simple “gate” inside the valve body that is raised or lowered into the water flow by turning the handle many times. When it is lowered fully the gate stops the water flow.
The ball valve has a “ball” with a hole drilled through it. Turning the handle one-quarter turn lines this hole up with the piping and allows water to flow. Turn the handle back one-quarter turn to turn off the valve. This quick on-off action can cause water hammer problems in some systems, so to be on the safe side always turn a ball valve on and off slowly. Both the gate and ball valve work well for manual systems.
The electric valve used with automatic timers is a diaphragm valve with a 24 volt AC solenoid. Apply 24 volts to the solenoid and the valve will open, remove the voltage and the valve will close. These valves also have a feature that will allow you to turn the valve on without electricity if necessary, but once manually turned on the valve must be manually turned off.
Some homeowners are concerned about the electric wires in the yard used to connect the electric valves to the timer. The 24 volt system used to operate the valves is similar to that used for model trains – enough voltage to open the valves, but not enough to pose a shock or electrocution threat should you accidentally cut a wire with a shovel.
Any valve installed in the landscape should be placed in a valve box for easy access. The valve box is simply a small bucket with an easily-removed top, no bottom, and openings in the sides to allow pipe to run through. Valve boxes are installed with the top at ground level and are designed to allow lawn mowers to run over them with no damage. The tops are usually green to make them less conspicuous in the landscape. Any valve will require maintenance at some point, so always install them in valve boxes so that they can be easily found and repaired.
All municipal water systems require some type of anti-siphon or backflow prevention device. This device prevents water in the irrigation system from re-entering and possibly contaminating the drinking water system. Each water system determines the type of device required for their system.
The most common device is the double check valve. This is simply an assembly containing two check valves in series. The theory is that should one check valve fail, the second one will still operate and prevent backflow and possible contamination.
Some municipalities in coastal South Carolina require an anti-siphon device to be installed above ground instead of a backflow preventer. These devices work well when no ground elevation is present in the system.
All backflow prevention or anti-siphon devices have a number of small test ports to allow testing of the device. South Carolina law requires that these devices be tested annually to make sure they are operating properly.
Irrigation systems may be operated manually with manual valves, or automatically with electric diaphragm valves and timers. All South Carolina landscape irrigation systems require some type of backflow prevention device if they are connected to a municipal water system.