Somewhere on your irrigation line, usually near the house or in a box near the meter, there is a backflow preventer. Most people never think about it until it starts leaking or a letter arrives asking for a test.
What backflow is
Your sprinkler system and your kitchen faucet share the same water supply. Inside the sprinkler pipes, water sits still between waterings. It can pick up soil, fertilizer, pesticide residue and bacteria, especially around heads that sit in the lawn.
Normally water only flows one way: from the city main, through your meter, out to the house and the sprinklers. But if pressure in the main drops, for example during a water main break or when a fire hydrant is opened nearby, water can be pulled backward. Without protection, water from the sprinkler pipes could be siphoned back into the house supply or even the public main. That is backflow.
A backflow preventer stops it with check valves and, depending on the type, an air inlet that breaks a vacuum.
Common types on homes
Pressure vacuum breaker (PVB). Very common on Dallas-area homes. It sits above ground, at least a foot above the highest head, with a ball-valve on each side and a bonnet on top. It has a spring-loaded check valve and an air inlet.
Double check valve assembly. Two check valves in series, often installed in a box below ground. Common in some areas and where above-ground devices are not wanted.
Reduced pressure zone assembly (RPZ). Used where the hazard is higher, such as commercial properties or systems with fertilizer injection. It has a relief valve that dumps water if the checks fail.
Which type is required depends on local rules and the system.
Why they leak
Water spraying from the top when the system starts. On a PVB, a brief spit when the system pressurizes can be normal. Continuous spray usually means the air inlet poppet is not seating, often because of debris or a worn seal.
Dripping from test cocks. The small test cocks can leak if left partly open or if their seals fail.
Cracks after a freeze. The device is full of water. When it freezes, it can crack. See getting through a hard freeze.
Worn internal parts. Springs and rubber seals wear out. Repair kits are available for many models.
Testing
Backflow assemblies are tested with a special gauge kit by a licensed backflow prevention assembly tester. The tester checks that each check valve holds and that the air inlet or relief valve opens when it should. Results are typically reported to the water provider on a form.
Whether and how often your device needs testing depends on your water provider and the type of device. Some providers require testing at installation, at certain intervals, or when a device is repaired or replaced. If you get a notice, it will usually include a deadline. Call us with the details and we will help.
Installation rules
Backflow devices need to be installed correctly to work. A PVB, for example, has to be above the highest downstream head. New irrigation systems require a backflow device and, in many cities, a permit and inspection. Texas requires irrigation work to be done by or under a licensed irrigator.
When the system will not get water
If the zones run but no water comes out, check whether the ball valves on the backflow device are open. They are often closed for winter or after a repair and forgotten. The handles should be in line with the pipe when open.
Do not just remove it
Sometimes people remove a leaking backflow device and connect the pipe straight through. That is a health risk and against code. If the device is leaking, close the irrigation shut-off and have it repaired or replaced.
Call us
If your backflow device is leaking, cracked, or due for a test, call 469-208-4222. Tell us what you see and, if you have a notice, the deadline.
Have a question this did not answer? Call 469-208-4222 and ask. More articles on the blog.
