The Principle Operation of a Dual Check Valve Backflow Prevention Device – No Flow or Static State
When the DuCV is in a no-flow or static state, both check valves are closed tight if they are operating properly or not fouled. A no-flow or static state is created when there is no downstream demand or a downstream shut-off valve is closed drip tight. In the static or no flow state, the tensile strength of the check valve springs creates a pressure loss across the check valves. Since the minimum tensile strength of the check valve spring is 1 PSI, the pressure loss across the check valve is 1 PSI during a no-flow or static state. The DuCV has two check valves with similar check valve tensile strength, therefore, the minimum pressure loss created by the check valves would be 2 PSI.