Pneumatic Pilot operated check valve – function and application
Stop valves (also known as pilot-operated check valves or stop fittings) are frequently used in pneumatics when it is necessary to stop a cylinder or motor quickly and accurately as well as to increase plant safety.
You ask yourself why not stop a cylinder at the desired position with a 5/3 directional control valve with center closed. Well - the directional control valve is a piston spool valve with the disadvantage that it has a certain leakage rate due to its design. If the actuator is to be held for a longer period of time, this leakage may become noticeable. In addition, directional control valves often cannot be installed close to the actuator, thus increasing the risk of hose burst. In addition, the time delay rises with increasing hose length due to the compressibility of the compressed air.
Stop valves are exactly the right solution here. As so-called poppet valves, they have no leakage, can be mounted directly to the actuator and thus ensure maximum safety.
The following shows a few circuit examples of how the pilot operated check valve can be used:
Function: Supplying pressure to the pilot port allows air flow in the opposite direction. In the case of a pressure drop, the stop valve closes immediately and ensures that a cylinder cannot sag uncontrolled.
Important for circuit design: The stop valve can only close safely if its pilot port is vented!