The Principle Operation of a Dual Check Valve Backflow Prevention Device – Pressure Loss Across Check Valves – Dynamic State
As water is flowing through the DuCV, 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 springs are force loaded to a minimum of 1 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. 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. The pressure loss indicated on the graph at zero gpm is due to the tinsel strength or force of the springs. The DuCV can be used on residential fire sprinkler protection systems and it is important to keep the pressure losses to a minimum. As the rate of flow increases, the pressure loss becomes greater. A 1 inch DuCV with a flow rate of 10 gpm will have a pressure loss across the DuCV of about 5 psi. Maximum allowable pressure loss across the DuCV is 10 psi.