How do I Test a Backflow Valve?

Backflow valves, also known as check valves, allow water to flow only in one direction. When installed properly, backflow valves prevent water from entering a homeowner's water system and becoming contaminated then re-entering the public water supply. Check valves may also be installed in different segments of a home's water system to segregate laundry or sprinkler systems from drinking water. Most municipalities require that backflow valves be installed and maintained and sometimes require a qualified technician's certification that they operate properly.

Backflow valves keep water from re-entering the public water supply after entering privately owned pipes.
  1. Shut off the main water supply so the overall water pressure in the building being tested is neutral.

  2. Locate the backflow valve and, using the diagrams on the valve, determine the direction water flows through the valve.

  3. Bleed test cocks to free them of dirt and accumulated water pressure by turning them open using a screwdriver.

  4. Insert the differential gauge's low pressure hose into the test cock closest to the water supply (the upstream cock).

  5. Insert the differential gauge's high pressure hose into the downstream test cock.

  6. Bleed the high-pressure hose and the low-pressure hose to clear any air or water from the gauge. Record the pressure differential between the two segments. A differential pressure of at least 1 psid indicates a working and tightly sealed pressure gauge.

  7. Turn the building's main water supply back on.