Sprinkler Valve Repair: How Zone Valves Work and Why They Fail

Every zone in your sprinkler system is controlled by a valve. When the controller tells a zone to start, the valve opens and water flows to that zone’s heads. When time is up, the valve closes. Valves do this every watering day for years. When one fails, the result is a zone that will not run, a zone that will not stop, or a slow leak that keeps water trickling out of the lowest head. This article explains how valves work and what goes wrong.

Where Your Valves Are

Most residential valves sit in green or black plastic boxes buried flush with the ground. They are often grouped together in one or two boxes near the house, a side yard or a corner of the lawn. Some systems spread valves out around the yard. Our guide to finding buried valve boxes can help if yours are hidden under grass or mulch.

How a Zone Valve Works

A typical in-ground valve has these parts:

• Body: the plastic housing with an inlet from the mainline and an outlet to the zone’s lateral pipe.
• Diaphragm: a flexible rubber disk inside that seals against a seat to stop water.
• Bonnet: the top cover that holds the diaphragm in place.
• Solenoid: an electric coil on top that opens a small passage when the controller sends power.
• Flow control: a handle or knob on some valves that limits how far the diaphragm can open.
• Bleed screw or lever: lets you open the valve by hand for testing.

When the valve is closed, water pressure sits on top of the diaphragm and holds it down against the seat. When the solenoid gets power, it opens a tiny port that lets water above the diaphragm escape. Pressure underneath then pushes the diaphragm up, and water flows through. When the power stops, the port closes, pressure builds above the diaphragm again, and the valve shuts.

Because the valve depends on small passages, a tiny bit of sand or debris can keep it from working correctly.

Common Valve Problems

A zone will not turn on

The valve is not opening. Causes include a bad solenoid, a broken wire, a controller problem, a closed flow control or debris blocking the small ports. Our step-by-step guide on a zone that will not turn on walks through diagnosis.

A zone will not turn off

The valve is not closing. Causes include debris on the diaphragm seat, a torn diaphragm, a solenoid stuck open, a bleed screw left open, or a controller that is still sending power. See our article on a zone that will not turn off.

Water weeps from the lowest head after the zone stops

If water keeps trickling from the lowest head for a long time, the valve may be leaking slowly through its seat. A short trickle after shutoff, though, is usually just water draining out of the pipe. Our article on low-head drainage explains the difference.

Water leaks from the top of the valve

A leak from the bonnet or solenoid often means a loose bonnet, a cracked body, or a solenoid that is not seated. Tightening the bonnet screws evenly or reseating the solenoid sometimes fixes it.

The valve chatters or hammers

A valve that chatters or makes a banging noise when it closes can have debris in it, a worn diaphragm or pressure that is higher than it should be.

Clean, Rebuild or Replace?

Many valve problems can be solved without replacing the valve:

1. Clean it. Shut off the water, remove the bonnet, rinse the diaphragm and the seat, clear the small ports, and reassemble.
2. Replace the diaphragm. Worn or torn diaphragms are common after years of service. Many brands sell rebuild kits.
3. Replace the solenoid. Solenoids can be tested with a multimeter and replaced by unscrewing the old one.
4. Replace the valve. If the body is cracked, parts are not available, or the valve has failed repeatedly, replacement is the better choice.

Replacing a valve means cutting pipe and gluing in a new one, often in a muddy box. It is doable for handy homeowners but is easier with experience.

Why Valves Fail in Fort Worth

A few local conditions play a part. Clay soil gets into valve boxes and around fittings. Mud washing into boxes can bury valves. Fine sediment and grit from pipe repairs can get into valves and keep them from sealing. Freezes can crack valve bodies that sit high in the box. Wires in wet boxes corrode if splices are not waterproof. Our article on valve wiring problems covers wiring issues in detail.

Keeping Valves Healthy

• Open valve boxes once a year and clear out mud, roots and insects.
• Make sure wire splices use waterproof connectors.
• Flush lines after any pipe repair so grit does not reach the valves.
• Fix mainline leaks promptly so boxes do not stay flooded.

Matching Replacement Parts

Valves from different brands, and even different models from the same brand, use different diaphragms and solenoids. Before you buy parts, look at the top of the valve for a brand name and model number, or take a clear photo to the store. Some older valves are no longer made, and rebuild kits for them can be hard to find. In that case, replacing the whole valve is often simpler. If several valves in one box are the same old model and one has failed, the others may not be far behind, and replacing the set at once can save a second trip into the box later.

When to Call a Technician

If a valve will not close and cleaning did not help, if you cannot find the valve, or if several valves are acting up, a technician can diagnose it quickly. Our sprinkler repair service repairs and replaces all common residential valve brands.