The prime function of a check valve is to protect mechanical equipment in a piping system by preventing reversal of flow by the fluid. This is particularly important in the case of pumps and compressors, where back flow could damage the internals of the equipment and cause an unnecessary shutdown of the system and in severe cases the complete plant.
Generally speaking check valves have no requirement for operators, and so the valve is operated automatically by flow reversal; however, in very special circumstances this uni-directional facility has to be overridden. Check valves either can be fitted with a device that allows the closure plate(s) to be locked open or alternatively can have the closure plate(s) removed. The latter alternative requires dismantling the valve, removing the plates, and re-installing the valve.
Check valves are automatic valves that open with forward flow and close against reverse flow.
This mode of flow regulation is required to prevent return flow, to maintain prime after the pump has stopped, to enable reciprocating pumps and compressors to function, and to prevent rotary pumps and compressors from driving standby units in reverse. Check valves may also be required in lines feeding a secondary system in which the pressure can rise above that of the primary system.
Check valves may be grouped according to the way the closure member moves onto the seat. Four groups of check valves are then distinguished:
Lift check valves. The closure member travels in...
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