design of a check valve
Single wing-Check Valves have been used for a hundred years as a means to prevent backflow. Unfortunately, a simple check valve is not leak proof, and conditions were found where the single check valve was allowing water to back up into the public system. Then double swing-check valves were used, doubling the reliability of backflow prevention.
An improvement in the swing-Check Valve was the addition of weight inside the valve body and hung on the downstream face of theCheck Valve. The additional weight prevented the swing check from floating open and allowing seepage backwards through the valve and into the public side of the piping. A down side to the design of many older check valves is the inability to actually test the valves to verify that the valves are seating positively.
Today, the design of the check valves for fire systems has improved significantly. Many newer backflow prevention check valve assemblies do not rely on a swing check system. They use a more sophisticated spring loaded system in which the seat moves perpendicular to the valve seat. Other valves which are of the swing design have a spring loaded cam arm to maintain positive seating force against the top of the clapper. Most valves have means of testing the valves to verify that the seats are definitely holding. Most of the valves available today are on an angled seat that create a greater differential over the face of the clapper to help hold the valve closed. Many are weighted or spring loaded.
