Here’s the final part of our 3 part series on hydraulic trouble shooting 101.
STEP 5 – Relief Valve…
If the test in STEP 3 has indicated the trouble to be in the relief valve, point D, the quickest remedy is to replace the valve with one known to be good. The faulty valve may later be disassembled for inspection and cleaning.
Pilot-operated relief valves have small orifices which may be blocked with accumulations of dirt. Blow out all passages with an air hose and run a small wire through orifices.
Check also for free movement of the spool. In a relief valve with pipe thread connections in the body, the spool may bind if pipe fittings are over-tightened. If possible, test the spool for bind before unscrewing threaded connections from the body, or screw in fittings tightly during inspection of the valve.
STEP 6 – Cylinder…
If the pump will deliver full pressure when operating across the relief valve in STEP 2, both pump and relief valve can be considered good, and the trouble is further downstream. The cylinder should be tested first for worn-out or defective packing by the method described in our guide “Cylinder and Valve Testing”. Other Components…
Check other components such as bypass flow controls, hydraulic motors, etc. Solenoid 4-way valves of the pilot-operated type with tandem or open center spools may not have sufficient pilot pressure to shift the spool.
If you still have problems…
If you still have questions or problems after trying to troubleshoot your hydraulic system, feel free to give us a call and have one of our hydraulic specialists come and give you a hand.
Is it necessary to deglaze the cylinder tube and how do you do it?
While it’s not always necessary, it’s usually a good idea. After long periods in service, the internal surface of cylinder tubes can actually become too smooth. As a result, the replacement seals may leak.
Deglazing/deburring also removes spot rust and other minor surface imperfections – which is essential for optimum seal life.
The tool that’s most often used for this job is a Flex-Hone. The correct technique for using one is shown in the video “How to Use a Flex-Hone”:
If your going to try to repair your hydraulic cylinders, it’s well worth three minutes of your time.
Ballooning of the cylinder tube is usually caused by excessive honing or insufficient wall thickness and/or material strength for the cylinder’s operating pressure.
Once the tube balloons, the correct tolerance between the piston seal and tube wall is lost, and high-pressure fluid bypasses the seal. This high velocity fluid can erode the seal and localized heating caused by the pressure drop across the piston reduces seal life.
Insufficient Bearing Area
If the internal bearing areas in the gland and on the piston are insufficient to carry the torsional load transferred to the cylinder, excessive load is placed on the rod and piston seals. This results in deformation and ultimately premature failure of the seals.
The surface finish of the cylinder rod can have a dramatic effect on the life of the rod seal. If the surface roughness is too low seal life can be reduced through inadequate lubrication.
If the surface roughness is too high, contaminant ingression is increased and an unacceptable level of leakage can result.
Keep in mind that not all hydraulic cylinders are made equal. So if you have hydraulic cylinders that suffer recurring failure, it’s likely that modifications to the cylinder are required to break the vicious circle of failure and repair.
Check out “The Beast”
Okay so it isn’t exactly a beast BUT it is a huge bench that allows us to test every aspect of any hydraulic component.
When you have us repair or rebuild any hydraulic component, it goes through rigorous testing on our hydraulic test stand.
We use the test stand for: