In order to design a sprinkler or drip irrigation system for the lawn, we must first know how much flow is available in gallons per minute from the water source. This will depend on the pump or size of the water meter used. In this example let’s assume we have a 5/8" water meter and that the available flow is 12 gallons per minute. If the design requires the use of 12 sprinklers with a discharge rate of 32 gallons per minute each, then you can see that only 3 sprinklers may be operated at one time. Since we have 12 sprinklers and only 3 may be operated at once then the system must be divided into 4 separate zones. Four control valves would be necessary so that each of the zones may be controlled separately. Drip irrigation systems may be zoned in a similar manner.

The control valves which operate each zone may be controlled either manually or automatically depending on the operator’s preference. If the irrigation system is fairly extensive, consisting of four or more separate zones, it is usually desirable to use automatic controls.

A simple gate valve or ball valve is all that is necessary to operate a manually controlled irrigation system. These valves may be constructed of bronze or plastic.

Automatic systems typically utilize electrically actuated solenoid valves although in some case hydraulically actuated valves may be used. The electric valves are activated by 24 volt electric current. The control wires are generally buried in the same trench with the pipeline.

Electric solenoid valves and manual control valves are usually buried underground in plastic boxes with covers. This gets the valves out of the way and makes them easily accessible. If the valves are installed above the ground, provisions should be provided for draining the pipes during the winter months.

Automatic time clock controllers are usually used to control automatic irrigation systems. Most of these units will control several stations and will allow you to program a 14-day watering schedule. Some of these systems use electro-mechanical controls while others use solid state controls. The electro-mechanical controllers are somewhat more expensive, but they are generally less susceptible to lightning damage than the solid state controller. Most irrigation controllers can be equipped with a rainfall sensor which will keep the irrigation system from operating in the event of rainfall.

For simple systems attached to an outside faucet you can also purchase devices which will turn the system off after a preset time. These devices are very simple and will generally pay for themselves in savings on your water bill.

There are also devices which will actually measure the moisture content in the soil. These can be either read manually or equipped with a switching device which can automatically turn an irrigation system on and off. These require regular maintenance however, and are not used extensively in homeowner applications. Some controllers also offer the option of including a rainfall switch which will override the controller if a significant rainfall occurs. These are relatively inexpensive and can be invaluable for anyone who cannot regularly monitor their system.