Dual Check Valve Backflow Prevention Device – Backflow Backsiphonage Condition – First or Second Check Valve Not Drip Tight

When the DuCV is in a normal flow condition and there is a demand downstream, the checks valves are open. During the normal operations of a DCVA the springs are closed when there is no demand downstream. If a backsiphonage condition were to occur in inlet piping system, the first and second check valves would close tight with the assistance of the spring, if they were not fouled and operating properly. When backsiphonage occurs, the first check valve will close before the second check valve due to the negative pressure created upstream of the first check valve in the inlet piping system. If the first check valve is fouled and does not close, the DuCV is still providing protection if the second check valves closed drip tight. If the second check valve was fouled with debris and could not close tight, the first check would hold tight and the device would still provide protection. If both check valves were fouled as well under a backsiphonage condition, the device would not offer protection. The status or condition of the check valves cannot be determined since the DuCV is not inline testable. Since the condition of the DuCV cannot be evaluated inline, it should not be used to control hazardous cross-connections but should only be used for hydraulic purposes such as service line protection. Service line protection prevents the flow of a potable water system into another potable water system. The amount of non-potable water entering the potable water system during a backflow condition is dependent on the degree of the fouled check valves. If the check valves were fouled by a small amount of debris a small amount of non-potable water would enter the potable water system. If the check valve disks were badly damaged a large amount of non-potable may enter the potable water system.