Pilot Operated Check Valve
A pilot operated check valve is a lock valve that normally allows flow in one direction only but can also be opened in the reverse direction by pilot pressure from the opposite line. Because sealing when closed is achieved by a cone seat, it holds the load fixed for long periods. The pilot ratio is typically between 3:1 and 4:1.
The micron-level internal leakage of spool valves causes a suspended load to drift within hours. A pilot operated check valve placed at the cylinder port closes this path: fluid passes freely as it enters the cylinder, while its exit is locked by the cone. When you want to lower, pressure applied to the opposite port lifts the cone via the pilot piston.
- Pilot ratio: a 4:1 ratio means that pilot pressure equal to one quarter of the load pressure is enough to open the valve.
- Typical problem: if there is back pressure in the tank line, the valve does not close fully or opens and closes with chatter.
- Difference: unlike a load holding valve, it does not control lowering speed; it only locks or opens.
With a load slowly drifting in neutral, the decisive question is this: does the drift come from the lever itself or from the lock valve? If you disable the electronic remote control completely, move the lever manually to neutral, and the drift continues, the problem is on the hydraulic side.
Where this term is used: Connect Plus and Minus, Run: Installation That Does Not Depend on Technical Staff