The Principle Operation of a Dual Check Valve with Intermediate Atmospheric Vent – Backflow Prevention Device

The Dual Check Valve with Intermediate Atmospheric Vent (DCVwIV) is a backflow prevention device designed to prevent the non-potable from enter the potable water system during a backflow event in the plumbing system. The DCVwIV is equipped with two independent operating spring-loaded check valves and an atmospheric vent located in an intermediate chamber between the two check valves. Each check valve is designed to hold at least 1 psi in the direction of flow. The check valves are force loaded to a normally closed position, and the venting of intermediate atmospheric vent is force loaded to a normally open position. The intermediate atmospheric vent is designed to break the vacuum during a backsiphonage event. The DCVwIV is equipped with a pressure-activated diaphragm, which is located on the inlet side of the intermediate atmospheric vent that closes when subjected to line pressure. Line pressure pushing on a diaphragm keeps the atmospheric vent close. If the line pressure is zero psi or if backsiphonage is present, the intermediate atmospheric vent will open to the atmosphere. With the vent open, the area between the check valves is atmospheric. The DCVwIV is capable of being used under constant pressure and can be used where backpressure or backsiphonage is present. The DCVwIV is suitable for hot or cold water service installations with an inlet temperature range of 40 to 210 degrees F and a backflow maximum temperature of 250 degrees F. Hot water use may be limited by the manufacture specification. The maximum working pressure is 150 psi. The minimum required inlet pressure is 25 psi. The DCVwIV sizes range from ¼ inch and ¾ inch sizes. The DCVwIV is equipped with an internal strainer screen. The DCVwIV is not equipped with test cocks or upstream and downstream shut-off valve therefor; the DCVwIV is not listed as an “assembly.” The DCVwIv is classified as a backflow prevention device that can be installed vertically or horizontally. The DCVwIV shall only be used for low hazardous situations where there are no chemical hazardous being used downstream. The DCwIV shall comply with ASSE Standard 1012.