How an Irrigation Solenoid Valve Works

Irrigation solenoid valves are the standard mechanism found in electrically operated home sprinkler systems as well as larger industrial-made crop sprinklers. For all the complexity of these watering systems, the irrigation solenoid valve is surprisingly simple and works on basic principles of fluid pressure imbalance.

The irrigation solenoid valve is a single chamber divided by a plastic or rubberized diaphragm. A thin spring pushes against the back of the diaphragm, blocking off the water inlet from the water outlet. Behind the diaphragm, near the water outlet, is a tiny cylindrical chamber that connects to the water flow. In this chamber sits a piston which is held in place by another metal spring. This spring is actually the solenoid. The cylinder has another port which is open to the air, and when the solenoid spring has no electricity running through it, the piston is in its forward position, allowing air to pass from the cylinder into the valve's primary chamber. It is this air and the simple atmospheric pressure it creates which prevents water from squeezing past the diaphragm.

The irrigation solenoid valve is activated by means of a small electric current which is sent into the solenoid spring. The solenoid spring becomes, for all intents and purposes, a tiny magnet. It coils tighter as a result of its own magnetic properties and pulls the piston backward. This seals off the hole allowing air into the chamber. Because the source of air pressure has been removed, nothing is pushing against the outlet side of the diaphragm anymore.

Without this back pressure, the diaphragm is pushed out of the way by the force of incoming water, allowing water to pass freely through the irrigation solenoid valve. When the current causing the solenoid spring to coil ceases, air pressure is allowed back into the valve and seals the diaphragm shut.