How Irrigation Valves Work

The most complicated component of an irrigation system is the valve, so it's important for the homeowner to understand how irrigation valves work. Most valves are reliably built and will last for many years, but should you need to fix one, it's handy to know just what all those different parts do.

Valves are the gateway to every irrigation system – they control the flow of water. They can be manual – meaning that you open and close them by turning a handle – or electric, operating on a low-voltage current and controlled by a timer.

The diaphragm of the valve is more than twice the size of the opening to the pipe, and held in place by water pressure in the valve's upper chamber. When the valve gets a message to open – whether because the manual bleed's been opened or the automatic timer has sparked the solenoid – a small plunger inside the valve sends water into the lower chamber, lessening the pressure on the diaphragm and allowing the valve to open.

To close a valve, the automatic timer stops sending its electrical message to the solenoid, or the manual bleed screw is turned in the opposite direction, dropping the plunger and stops the flow of water from the upper chamber. The pressure on the diaphragm then closes the valve.

If a valve doesn't work, first check to make sure the water's turned on – it may seem painfully obvious, but sometimes the most obvious solution is the correct one! If it is, next test the electrical current in the automatic controller with a volt-ohm meter. The valve should be running at 24 volts AC. If it's not, there may be a blown fuse or, more problematic, a malfunction in the timer's transformer.

Dirt and debris should also be cleaned from the timer on a regular basis – if dirt gets trapped inside the valve, the diaphragm won't close all the way, causing leakage.

Making this simple repair is easy for most homeowners, once they've educated themselves on the basics of how irrigation valves work.