The Principle Operation of a Dual Check Valve Backflow Prevention Device – Backflow Backpressure – Condition Both Check Valve Holding Tight
During the normal operations of a DUCV the springs loaded check valves are closed when there is no demand downstream. The spring loaded check valves will open when there is a demand downstream except when there is a backpressure backflow occurrence created by a pump, elevated storage tank or due to elevation head or thermal expansion in the piping system. When this occurs, the second check valve will close and since the DuCV is in static state due to the backpressure and the closed second check valve, the first check valve will close as well. The DuCV is providing protection.