What should an operator inspect first if a reduced pressure zone backflow preventer leaks at the vent?

• A. Inspect the vent screen
• B. Inspect the last check valve
• C. Inspect the first check valve
• D. Inspect the pressure relief valve

Answer: (C)

Leaking at the vent usually points to a failure of the upstream, or first, check valve. The vent is the outlet from the space between the two check valves and the relief valve; if the upstream check valve doesn’t seal properly, upstream pressure can enter that space and push through to the vent. Inspecting the first check valve first targets the most common source of vent leakage: a worn seat, damaged gasket, or debris preventing a tight seal. If that valve appears to seal correctly, then proceed to check the relief valve and the second check valve for other possible causes.