Lawn sprinkler valves are generally constructed out of plastic, although some of the larger commercial model sprinkler valves are made from varying forms of metal.  Consisting primarily of a valve body, a water inlet and outlet port, a diaphragm and a seat in which allows the diaphragm to close the valve.  Receiving a signal from an irrigation controller either via wiring or wireless receiver, the vavle seats off restricting the flow of water to a sprinkler head.  Most models are constructed with a manual valve to enable the valve to be manually operated, and some models include seating adjustments, flow control and drain mechanisms.  Replacement parts are widely available to allow for quick and easy maintenance on items such as the diaphragm which can be worn down over time from the flow of water across the diaphragm as well as dirt and other impurities which can cause minute scratches.