Occasionally, a homeowner will discover a valve in their sprinkler system is leaking. The immediate fear that many have is that the entire valve needs to be replaced which would involve digging, cutting and gluing pipe, and a lot of work, but the good news is that valves can often be repaired without much effort. The beauty of sprinkler valves is how simple they are with only two moving parts. The first is a diaphragm, or a rubber seal that blocks the flow of water when the valve is closed and lets water flow when the valve is open. The second moving part is a solenoid (yes a word that most of us have not used since our high school physics class). Simply put, a solenoid consists of a metal rod, a spring, and an electromagnet. When there is no current the spring pushes the metal rod out and it blocks a little port in the valve. When the port is blocked the water pressure builds up on the back side of the diaphragm and it seals the valve. This is the off position. When an electrical current is applied to the solenoid, it activates the electromagnet and pulls the rod away from the port in the valve. This releases the pressure on the back side of the diaphragm which allows the valve to open for as long as that current is present.

When something goes wrong in a valve it usually comes down to one of three things:

A faulty solenoid - the solenoid no longer opens or closes properly when a current is applied.
A damaged or obstructed diaphragm - if the diaphragm rips or has dirt obstructing it then the valve will not seal properly and the valve will leak.
A damaged valve body - a physical crack or damage to the valve itself that usually causes the water to leak at the valve itself.

The solenoid and the diaphragm are both easy for the average homeowner to replace. The chart below shows which solenoids and diaphragms work with which valves.

Compatible Diaphragms and Solenoids

Diaphragm Support Ring for Jar Top Valves