The Double Check Valve Device Assembly – Rate of Flow and Pressure Loss
As water is flowing through the DCVA, a force is needed to open the check valves since they are spring loaded. That force exerted on the check valves is expressed in pounds per square inch (PSI). The greater the flow in gallons per minute (GPM), the more the check valves will open. As the gallons per minute increases, the pressure loss through the assembly is greater. According to the Flow Rate Chart, a 3-inch DCVA in a static state with a 0 GPM flow rate will have a pressure loss of approximately 4.0 PSI. The same DCVA at a flow rate of 150 GPM will have a pressure loss of approximately 5.0 PSI. As the rate of flow increases, the pressure loss becomes greater. This concept of pressure loss relationship to flow rate is important to understand because at zero GPM, the check valve should be closed drip tight and the pressure loss indicated on the graph is due to the tinsel strength or force of the springs. When testing a backflow prevention device assembly, the test shall be completed during a static state (0 GPM) since that is when the check valves should be closed.
