Backsiphonage Backflow – Relief Valve Opened – First and Second Check Valves Closed
During a backsiphonage situation, the inlet pressure is sub-atmospheric. Since there is no inlet pressure to keep the relief valve closed, the relief valve opens with the assistance of the spring discharging the small amount of water that was in the zone. The first and second check valves would close tight on condition that they are not fouled. With the relief valve opened, atmospheric pressure is pulled into the device through the relief valve port creating an air gap separation between the potable and non-potable sources. The pressure in the zone is now atmospheric. The pressure upstream of the first check valve is negative or sub-atmospheric since the first check valve is closed tight. The pressure downstream of the second check valve is positive since it is closed tight. The RPZ is providing protection since it is preventing non-potable water from enter the potable water system.