In fact a counterbalance valve is an improved pilot operated check valve. An important and major difference between these two valves is: - the opening pressure of a pilot operated check valve depends on the pressure (applied by the load) behind the valve; - the opening pressure of a counterbalance valve depends on the spring pressure behind the valve. The dynamic performance of a counterbalance valve is many times better than the dynamic performance of a pilot operated check valve
The counterbalance valve is normally located in the line between a directional control valve and the outlet of a vertically mounted actuating cylinder which supports weight or must be held in position for a period of time.
This valve serves as a hydraulic resistance to the actuating cylinder. For example, counterbalance valves are used in some hydraulically operated forklifts. The valve offers a resistance to the flow from the actuating cylinder when the fork is lowered. It also helps to support the fork in the UP position.
Counterbalance valves are also used in air- launched weapons loaders. In this case the valve is located in the top of the lift cylinder. The valve requires a specific pressure to lower the load. If adequate pressure is not available, the load cannot be lowered. This prevents collapse of the load due to any malfunction of the hydraulic system.
In a counterbalance valve, a valve body is provided with a valve bore having first and second pump-side ports, first and second motor-side ports and an auxiliary port. A spool is slid ably fitted in the valve bore in a longitudinal direction thereof to establish and block communication between the respective ports. Left and right springs maintain the spool at a neutral position in which the respective ports are closed. A left pressure receiving chamber shifts the spool by a pressure oil supplied therein to a first traveling position at which the first pump-side port and the auxiliary port are communicated with each other and the second pump-side port and the second motor-side port are also communicated with each other. A right pressure receiving chamber shifts the spool by a pressure oil supplied therein to a second traveling position at which the second pump-side port and the auxiliary port are communicated with each other and the first pump-side port and the first motor-side port are communicated with each other. The spool is formed with a first axial bore communicated with the left pressure receiving chamber, a second axial bore communicated with the right pressure receiving chamber, first and second small diameter bores communicating the first and second axial bores with the first and second pump-side ports, respectively, and first and second large diameter bores communicating the first and second axial bores with an outer peripheral surface of the spool.
There are something must be taken attention when Setting Counterbalance Valves. It is critical first to check that the maximum pressure that can be generated by the load is not higher then the maximum setting of the counterbalance valve fitted.
1. Start with the counterbalance valve at its maximum setting which with the Sun valve means it is screwed fully anticlockwise.
2. Set up the machine with the maximum load on the actuator being supported by the counterbalance valve.
3. Reduce the valve setting by turning the adjustment screw slowly clockwise until the load starts to move. An extended allen-key wrench may be needed because the strong springs in the valve make them difficult to adjust under pressure.
4. Operate the machine to a condition where the counterbalance valve is no longer supporting any load.
5. Turn the adjust screw in fully (clockwise) to the minimum setting, counting the number of turns.
6. Add 30% to the number of turns and then re-set the valve (turn adjustment anti- clockwise) to this setting. Re-torque the locking nut and fit protective cap if required.