The Principle Operation of a Dual Check Valve with Intermediate Atmospheric Vent – Backflow Prevention Device – Backflow Backsiphonage
As water is flowing through the DCVwIV, the check valves are open and the intermediate atmospheric vent is closed. If a backsiphonage condition were to occur in the inlet piping system, the second check valve spring would force the check valve to seal against the check valve seat closing the second check valve. During the backsiphonage condition, the first check valve spring will force the first check valve to seals tightly against diaphragm closing the check valve and opening the intermediate atmospheric vent. Since the second check valve is closed tight, a minimal amount of water will discharge from the intermediate atmospheric vent when opened. With the intermediate atmospheric vent open, air in entering the area between the check valves breaking the vacuum and eliminating the siphoning of non-potable water into the potable water system. If the check valves are operating properly and the intermediate atmospheric vent opens, the DCVwIV is providing protection.
