Load Holding and Counterbalance Valve
A counterbalance valve is the valve that prevents the load from accelerating the cylinder and running away under its own weight, and that holds the load in place if a line breaks. Its setting pressure is typically chosen at 1.3-1.5 times the highest pressure generated by the load. Mounting it directly to the cylinder port is a safety requirement.
During lowering the valve creates a back pressure in the cylinder's outlet line. This pressure prevents the load from free falling and makes the motion dependent on the flow coming from the pump; that is, the load cannot accelerate and outrun the pump. It opens via pilot pressure from the opposite line.
- Mounting requirement: no hose may come between the valve and the cylinder. Otherwise, when that hose bursts the valve cannot hold the load. Widely accepted practices such as ISO 4413 require the valve to be as close to the actuator as possible.
- Setting error: too low a setting lets the load run away, while too high a setting causes unnecessary pressure drop and heating.
- Oscillation: on valves with a high pilot ratio, rhythmic bouncing can appear during lowering.
Electronic lever control does not replace this valve. The remote control bringing the motor to a safe center position within 250 ms on signal loss stops the oil flow; but what keeps a suspended load in place is the load holding valve on the hydraulic side.
Where this term is used: How Are Manual Hydraulic Levers Controlled Remotely? A Comparison of 6 Methods