Counterbalance valves are a regulating mechanism on valve-powered cylinders, such as those on electrical repair trucks. The counterbalance valves serve to limit the amount of fluid change within the flange, thus preventing sudden changes in pressure and resultant instability.
The valves work by reacting to the weight of the load as that weight is translated into pressure on the pump cylinder. For example, in a repair truck, the weight of the platform (and any repairmen within) supply the downward pressure to the cylinder. When the counterbalance valves are directly triggered by the force of the weight, which occurs when the load is being lowered or if the cylinder malfunctions, the valve restricts the amount of air or fluid that it releases.
As a result of the counterbalance valve's releasing fluid gradually, the load is stabilized and prevented from falling in a completely uncontrolled manner. Counterbalance valves are used as a safety mechanism, and to keep pressure cylinders stable as they contract to lower a load or release pressure.