The Double Check Valve Device Assembly – Pressure Loss

Installing double check valve 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).

Installing DCVA on service line could also create a cross-connection incident within the building. If there were unprotected indirect cross-connection downstream of the DCVA and a backsiphonage condition were to occur upstream of the DCVA, the check valves would hold back the water in the domestic water system piping in the building. If a tap was opened within the building upstream of an unprotected indirect cross-connection, the siphoning action created by the opening tap would pull non-potable into the potable domestic water piping system creating a cross-connection incident. Controlling cross-connections where they exist is critical in protecting the health of consumers of water.

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 DCVA on the service line decreased the pressure by 10 PSI. The pressure at the cooling tower is now 10 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.