CHECK VALVE

Check valves are designed to prevent the reversal of flow in a piping system. These valves are activated by the flowing material in the pipeline. The pressure of the fluid passing through the system opens the valve, while any reversal of flow will close the valve. Closure is accomplished by the weight of the check mechanism, by back pressure, by a spring, or by a combination of these means. The general types of check valves are swing check, lift check, piston check, and butterfly check. A swing check valve allows full, unobstructed flow and automatically closes as pressure decreases. A lift check valve is commonly used in piping systems in which globe valves are being used as a flow control valve. A piston check valve is essentially a lift check valve. It has a dashpot consisting of a piston and cylinder that provides a cushioning effect during operation. Butterfly check valves have a seating arrangement and flow characteristics similar to butterfly valves. Consequently, butterfly check valves are frequently used in systems using butterfly valves.