Backsiphonage Backflow – Relief Valve Opened – First Check Valve Closed and Second Check Valves Fouled Open
During a backsiphonage situation with both the upstream and downstream shut-off valves open, the relief valve will be open. If the first check valve closes tight, the zone pressure will be atmospheric, since the relief valve is open. If the second check valve is fouled open, water will discharge continuously out of the relief valve, since the pressure downstream of the second check valve is positive causing the non-potable water to flow into the zone and out of the relief valve. The RPZ is providing protection by preventing non-potable water from enter the potable water system, since the first check valve is closed tight and the relief valve is open. Water will discharge out of the relief valve until the downstream piping system is void of non-potable water.