Check Valve
A check valve is a simple valve that allows fluid to pass in one direction only and closes in the reverse direction with a spring loaded ball or cone. The lowest differential pressure required to open it is called the cracking pressure and is typically selected in the 0.3-5 bar range. It prevents reverse flow and load drop in the circuit.
This seemingly unimportant element takes on several critical jobs in the circuit:
- Reverse flow prevention: it prevents pressurized oil from draining to tank through the pump when the pump stops.
- Line separation: if two pumps feed the same line it prevents one from pushing into the other.
- Anti-cavitation: it allows oil to be drawn from tank when the actuator speeds up due to the load and the pump cannot keep up.
Selecting the cracking pressure is a balancing act. If selected low the valve opens quickly but its sealing weakens; if selected high it adds a permanent pressure drop to the line and generates heat. The spring force also determines how fast the valve closes.
If the load drifts slowly in neutral, the seating surfaces of the check valves in the circuit should be checked for scratches or dirt. This kind of drift is independent of the control electronics; it continues even when the remote control is at zero and does not improve by changing settings.
Where this term is used: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods