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Troubleshooting A Counterbalance Valve 

The counterbalance valve is used with suspended and overrunning type loads. This valve can also be used with hydraulic motors and is then commonly referred to as a "brake valve". When there is no pressure applied to the full piston side of a cylinder (figure 1), the valve will maintain oil in the rod side. The two pilot lines shown act on different areas inside the valve. The ratio of these areas is usually 3:1 or 4:1. For explanation we will use the 3:1 ratio. The line connected between the valve and cylinder's rod side acts on a small piston area (1 square inch) inside the valve. To overcome a spring tension of 1,800 lbs, the pressure would have to build to 1800 PSI.

Since the load in the example is exerting a force of only 1500 PSI, the valve will remain closed. When necessary to lower the load, the full piston side of the cylinder is pressurized. The "remote" pilot line will then be pressurized to open the valve. The remote pilot line acts on three times the area (3 square inches) than the internal pilot line acts upon. 

Actually, 1,500 lbs of force is already being exerted by the load on the spring. Therefore, the remote pilot pressure only has to develope 300 lbs. of additional force. pressure only has to build to 100 PSI on the 3 square inche surface area to equal 300 lbs. of force. (figure 2). 

The pressure and the weight of the load will cause the valve to open, allowing the load to lower. If the load were to start dropping to fast , this would cause a pressure drop in the remote pilot line. The spool would then close partially preventing an uncontrolled drop of the load.

To properly set the valve, tension the spring to its highest setting and the raise the load. On some counterbalance valves, the the adjustment is turned counterclockwise to increase the spring tension. Now, turn the adjust the opposite direction very slowly. Take care not to position yourself underneath the load. Once the load starts to drift down very slowly, turn the adjustment until the drifting stops. Turn the adjustment a quarter of a turn in the same direction and then tighten the lock nut.

Troubleshooting the valve

When counterbalance valves fail they usually stick in the open condition. This results in the load slowly drifting downward. One common mistake with counterbalance valves is, when this problem occurs the cylinder is always changed first without inspecting the counterbalance valve. Contamination can cause the internal check valve or spool to stick open. Before removing the valve, lower the load to the ground. Insure the pressure inside the hydraulic lines has been bled down to 0 PSI. Remove the valve and inspect for broken springs, trash etc. Don't forget to inspect the internal checkvalve.

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Nothing is more expensive than unscheduled down time.  GPM’s customers know they can call whenever they have a troubleshooting issue they simply can’t resolve.  With over 50 years experience dealing with hydraulic failures, our consultants have the resources to help troubleshoot whatever hydraulic problem you encounter.  Whether you’re experiencing a total system outage, repeated component failure or just need a professionally designed preventive maintenance schedule, the consultants at GPM can help.  Call GPM for 

            In-plant  Troubleshooting                                                

            Leakage Problems                                                         

            Pressure Settings

            Shock Problems

            Preventive Maintenance Scheduling

            Hydraulic Troubleshooting Manual Development

            Startup Consulting and Recommendations

            Heat Problems

            Repeated Component Failures  

            Speed Problems

Do you want to learn more about how GPM can help you? Go to http://gpmhydraulic.com/troubleshooting.htm

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GPM Hydraulic Consulting, Inc.
Box 1376
Monroe, GA 30655
(770) 267-3787

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