The Principle Operation of a Dual Check Valve Backflow Prevention Device – Flow Capacity
When the DuCV is fully pressurized and there is a demand downstream, (dynamic state) the spring loaded check valve are open and the intermediate atmospheric vent closed. The greater the flow through the DuCV, the more the check valves will open. The greater the flow velocity, the greater the pressure loss across the DuCV. As the diagrams show, as the gallons per minute through the DuCV increases, the pressure loss in pounds per square inch increases. Consult manufacture literature or capacity rate for the specific DuCV. According to the flow rate chart, a 1 inch DuCV in a static state with a 0 GPM flow rate will have a pressure loss of approximately 4.0 PSI. The same DuCV at a flow rate of approximately 25 GPM will have a pressure loss across the DuCV of approximately 5.0 PSI.