Dual Check Valve with Intermediate Atmospheric Vent Backflow Prevention Device – Backflow Condition – Second Check Valve Not Drip Tight

As water is flowing through the DCVwIV, the check valves are open and the intermediate atmospheric vent is closed. If a backflow condition were to occur, the first and second check valve springs would force the check valves to seal against the check valve seat closing both check valves. In a backpressure condition, the intermediate atmospheric vent would be closed since water pressure continues to push against the diaphragm that closes intermediate atmospheric vent. In a backsiphonage condition, the intermediate atmospheric vent is open since there is no water pressure pushing against the diaphragm that closes the intermediate atmospheric vent.

If the second check valve were not operating properly or fouled open during the backsiphonage condition, the closing of the first check valve and the opening of the intermediate atmospheric vent would provide protection. The intermediate atmospheric vent will open because there is no water pressure pushing against the diaphragm that closes the intermediate atmospheric vent. During a backsiphonage condition with the second check valve fouled open, the DCVwIV is still providing protection because the first check valve is holding tight and the intermediate atmospheric vent is open allowing air to enterer the area between the check valves, breaking the vacuum and eliminating the siphoning of non-potable water into the potable water system.If the second check valve were not operating properly or fouled open during the backpressure condition, the closing of the first check valve would provide protection. The intermediate atmospheric vent may open under certain differential pressure conditions between the inlet and outlet pressures, during a backpressure condition with a fouled second check valve. However, the intermediate atmospheric vent may remain closed since there is still water pressure pushing against the diaphragm that closes the intermediate atmospheric vent. For this reason, the DCVwIV can only be used to control low-hazard cross-connection. During a backpressure condition with the second check valve fouled open, the DCVwIV is still providing protection because the first check valve is holding tight not allowing non-potable water to enter the potable water system and the intermediate atmospheric vent may open depending of the differential pressure status.