The backflow prevention device in your home's sprinkler system prevents hazardous contaminants from making their way into your city's municipal water system. Pesticide residue or pet waste on the sprinkler heads can contaminate the water in the sprinkler system pipes. Without a backflow prevention device, this contaminated water could flow backwards into the city water system if the water pressure in their pipes drops below the water pressure in your sprinkler system.
If the backflow prevention device detects that the pressure in the city water pipes is too low, a relief valve in the device will open, and the water in your sprinkler system will leak out onto the ground. Unfortunately, these devices are prone to leaking — valves can become stuck open, causing water to continually leak out. If your sprinkler system's backflow prevention device is leaking, read on to find out how you can fix it.
Inspect the Whole Assembly for Cracks
Cracks can cause the backflow prevention device in your sprinkler system to leak, and these are commonly caused when water freezes in the valve over the winter. Remove the bell cover from the valve by gently turning the nut on top using a wrench, and then examine the inside of the valve. If you notice any cracks, you'll have to replace the whole assembly. The leak can prevent the valve from maintaining the correct amount of pressure to stop water from flowing backwards into the city water supply.
Look for Sediment Clogging the Relief Valve
The most common cause of a leaking backflow prevention device is sediment in the seat of the relief valve. The relief valve's gasket needs to make full contact with the seat. If there's sediment in the seat or if the gasket is cracked, water will constantly leak out of the relief valve. Remove any sediment in the seat using tweezers or a toothbrush, and make sure that the gasket in the relief valve is in good condition. If the gasket is cracked, you'll need to replace it — you can purchase a repair kit for the model of device that you have, and it will contain a replacement gasket for the repair valve. You can remove the cracked gasket by hand and slide the new one on.
Examine the Second Check Valve
While less common than a stuck relief valve, the second check valve (the one closest to the pipes leading to your lawn's sprinkler system) can become stuck open as well. This creates constant backflow, raising pressure between the two check valves and causing the relief valve to open. You can fix this problem in the same way that you fix problems with the relief valve — remove sediment from the check valve seat and replace the check valve gasket if it's cracked.
Overall, sediment blocking the relief valve gasket is the most common cause of a leaking backflow prevention device. If you fix the problem and it occurs again, you may want to consider installing a filter upstream from your sprinkler system in order to remove excess sediment from the municipal water supply. If you can't find out why your device is leaking or if the fixes above don't fix the leak, call a backflow service company and have them inspect your sprinkler system — it's important to repair a leaking backflow prevention device, since they often don't function correctly if they're leaking.