Check Valves

Check Valves

Check Valves are mechanical valves commonly used in conjunction with other valves. Check valves are designed to restrict the flow of gases and liquids to one direction. Product flow in the correct direction opens the valve. If the flow reverses direction, the check valve closes.

Common Types: Single swing valves, double disc swing valves, lift-check, silent, ball-check, and cone-check.

Single disc swing valves are designed with the closure element attached to the top of the cap. The closure element can be pushed aside by the flow, but swings back into the close position upon flow reversal. These valves are not good choices in services with frequent flow reversal, as the disc is often pounded into the seat and wears quickly. These valves may be installed vertically or horizontally, although when mounted vertically a lever and counter-balance should be applied to reduce the valves tendency to stay open in situations where flow velocity changes slowly. The swing check is the most commonly used design of check valves as they do not restrict flow.

Double disc or wafer check valves consist of two half-circle disks hinged together that fold together upon positive flow and retract to a full-circle to close against reverse flow. The valve is inserted between two flanges. These are most commonly used liquid services. Wafer valves are popular because they are generally compact and have a relatively low cost.

Lift-check valves have a disc that is guided. Spring-loaded types can operate in either vertical or horizontal mounting. The style that lacks the spring must be mounted in such a way as to allow gravity to close disc. Composition disc valves are available for gritty liquid services.

Ball check valves contain a ball that sits freely above the seat which has only one through hole. The ball has a slightly larger diameter than the through hole. When the pressure behind the seat exceeds the pressure above the ball product is allowed to flow through the valve. But once the pressure above the ball exceeds the pressure below the seat, the ball returns to rest in the seat, forming a seal that prevents backflow.

Silent or center guide valves are similar to lift check valves, with a center guide extending from inlet to outlet ports. The valve stopper is spring and bushing actuated to keep the movement "quiet.”

Cone check valves use a free-floating or spring loaded cone resting in the seat ring as the closure element. Upon reverse flow, the cone is forced back into its seat preventing backflow.