The Double Check Valve Device Assembly (DCVA) – Flow or Dynamic State with Backpressure Second Check Valve Holding Tight and First Check Valve Fouled Open
When the DCVA is in a normal flow condition and there is a demand downstream, the checks valves are open. If a backpressure condition were to occur due to the activation of a pump for example, that created a pressure downstream greater than the supply or inlet pressure; the second check valve would close tight if it were not fouled or operating properly. If the downstream shut-off valve was open and there was no demand or no-flow downstream, and backpressure condition was created by thermal expansion of the water in the downstream piping system for example, the second check valve would close tight, if it were not fouled or not operating properly. When backpressure occurs, the second check valve will close before the first check valve due to the increase in pressure downstream of the second check valve. The first check valve will close after the second check valve, since the second check valve closing due to the backpressure condition creates a no-flow or static condition. If the first check valve is fouled and does not close, the DCVA is still providing protection. The status or condition of the check valves can only be determined at the time that the DCVA is tested.