Reduced Pressure Principle Backflow Prevention Device Assembly Pressure Losses
The RPZ is equipped with spring loaded check valves. Therefore, there is a pressure loss through the device. The pressure loss through the device may be expected to average between 10 and 20 psi within the normal range of operation, depending upon the size and flow rate of the device. The American Water Works Association maximum allowable pressure loss through the device is 14 to 24 PSI depending on size and flow rates.
Installing backflow prevention device assemblies on service line reduces the pressure downstream. In some cases, the reduction in pressure could be problematic if there is insufficient pressure to raise water to highest point of use. For example, 40 PSI will raise the water to a height of 92 feet head. (40 PSI X 2.31 ft /PSI = 92 feet) 55 PSI will provide water to the top of a building that is 80 feet tall leaving 20 PSI at the highest water tap, the cooling tower. Installing a RPZ on the service line decreased the pressure by 14 PSI. The pressure at the Colling tower was now 7 PSI. This may present a problem especially if the pressure at the service line decreased or the pressure within the building decreased causing the pressure at the cooling tower and possible within the building to become sub-atmospheric.
