The Principle Operation of a Double Check Valve Backflow Prevention Device Assembly The Double Check Valve Device Assembly (DCVA) – No-Flow or Static State
When the DCVA 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 the 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 DCVA has two check valves with similar check valve tensile strength, therefore, the minimum pressure loss created by the check valves would be 2 PSI.
