The Principle Operation of a Dual Check Valve Backflow Prevention Device – Backflow Backsiphonage 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. When there is a demand downstream, the spring loaded check valves will open except when there is a backsiphonage backflow occurrence in the inlet water supply piping system. When this occurs, pressure upstream of the first check valve is sup-atmospheric. Because of the backsiphonage situation in the inlet water piping system, the DuCV is in static state and the first check valve will close tight if not fouled or not working properly. The second check valve will close tight holding back pressurized non-potable water. There is positive pressure downstream of both check valves. If the check valves are closed tight, a siphoning situation of the non-potable water is prevented. If a backpressure backflow condition were to occur, both check valves would close tight if not fouled. The closed check valves prevent non-potable from siphoning back into the potable water system. The DuCV is providing protection.