This is accomplished by allowing pilot pressure to act on a pilot piston, thus opening the check valve and retracting the cylinder. Unlike a simple check valve, reverse flow is required through the valve to extend or retract the cylinder. Pilot operated check valves may be pilot to open or pilot to close. This type of check valve is referred to as a pilot operated check valve. This style of check valve is used when flow needs to bypass a pressure valve during return flow, as a bypass around a filter when a filter becomes clogged, or to keep flow from entering a portion of a circuit at an undesirable time.īecause of slight spool leakage on standard directional control valves, we must add a check valve to the circuit if we need to hydraulically lock a cylinder. The simplest check valve allows free flow in one direction and blocks flow from the opposite direction. Because of their sealing capability many designs are considered to have zero leakage. In-line check valves are classified as directional control valves because they dictate the direction flow can travel in a portion of the circuit. This section has been designed to help you understand how the different valves function and the strategy of where they are used in the system. And since check valves are zero leakage devices, we can use them to lock hydraulic fluid from the cylinders. Simply stated, these valves are used to maintain the direction that fluid flows through a system. Check valves are a simple but important part of a hydraulic system.

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