The Principle Operation of a Dual Check Valve Backflow Prevention Device – Check Valves and Check Valve Springs
The DuCV has two independently acting spring loaded check valves force loaded to a normally closed position in the direction of flow. Each check valve spring is loaded to a minimum of 1 psi. The check valves in the DuCV provide primary backflow protection. Since the DuCV is equipped with spring loaded check valves there is a pressure loss in a static state and a greater pressure loss in a dynamic state (as water flows through the DuCV). The pressure loss through the DuCV is dependent on the size and flow rate of the device. The maximum allowable pressure loss through the device at the rated flow is 10 PSI. In this exploded view of the DuCV, you can see the locations of the springs designed to open at 1 psi differential in the direction of flow and check valves that will remain closed until there is a demand downstream. The spring loading of the check valves provided the ability to “bite” through small debris that may be lodged on the check valve seat or disk and still seal drip tight. Unloaded check valves do not have this feature. The check valve loading is a critical part of the design of the DuCV.