Backsiphonage Backflow – Relief Valve Opened – Both Check Valves Fouled Open
Atmospheric pressure is pulled into the device through the relief valve port and back through the fouled first check valve creating an air gap separation in the piping system. The zone pressure is sub-atmospheric as is the pressure upstream of the first check, since it is fouled open. The second check valve is fouled open and the pressure downstream of the second check valve is positive causing the non-potable water to enter the zone. The water downstream of the RPZ will continue to drain out of the relief valve until there is no water available in the downstream piping system or non-potable water will discharge continuously from the relief valve port as long as there is a positive pressure downstream of the second check valve.