Counterbalance valves are hydraulic devices that function using this basic principle: fluid can freely flow through a check valve into the actuator, and reverse flow will be blocked using a relief valve until a pre-set pressure is reached that is set based on the system pressure and load capability. This pressure is higher than the system pressure when the load is applied and allows the fluid to flow in the opposite direction and the actuator to function. When pressure is removed, the valve goes below this set value, closes, and the load holds its place.
The preset pressure to the pilot port will determine the direction the load can move. To lift a load, the valve allows free flow through the check valve, so the cylinder can extend. When fluid flows to the rod end of the cylinder, this pressure will pilot open the valve, so you can lower the load. This pressure will decrease if the load starts to run away, and the counterbalance valve will adjust to match the cylinder speed to the pump flow.
