Troubleshooting Challenge: Valve Change Delays Cylinder’s Motion

Troubleshooting Challenge: Valve Change Delays Cylinder’s Motion

The hydraulics used on a press had a pilot-operated directional valve that developed a leak at a construction plug. The company needed a gauge to set the main pump pressure and used a construction plug hole in the directional valve for the gauge. However, although the port was an SAE O-ring connection, the technician forced an NPT fitting into the port, causing an unfixable leak.

The company discovered a used valve in its storeroom with the same tandem spool set up and installed it. But then they had a problem with the system taking 14 to 16 sec. before the cylinder would move. Technicians ensured the pilot-operated relief control orifice was clear of any obstruction, but the delay continued.

Three easily identifiable issues i would question first. After valve replacement why did they need to set pump pressure again? was the return filter changed? This opens a can of worms that indicate a pressure relief valve possibly defective, to a pump being weak though, not ruling it out, I would do a flow test if no other cause is found? The fitting error could have potentially damaged the pump. Though not likely being down stream. However, the control valve they found and replaced could be questionable. does it have the capacity to handle the load, is it compatible with the system? The solenoid valves on the pilot operated controls. are they operating properly? is the solenoid compatible with the pressure requirements of the main control valve, cylinder and load needed to move them?
secondly i would look at he main valve, is the spring tension on the valves too great that the pilot system has to build enough pressure to over come spring force?
Third I would be looking for leakage around the valve spools in the pilot circuit and main circuit.
Simply put i would start from simple to more complex, based on the information provided. There are several possible reasons as to why. The easiest would be to research the part number and specifications of the valvebody they installed. the giveaway is needing the main pressure needing reset. though other factors could play into this. pressure test the relief valve for proper operation with a 4000PSI full open pressure, pressure test it to cracking pressure 250 -500 PSI below full open pressure, and pilot relief, cracking pressure, just to see if they hold. If either cannot hold cracking pressure for thirty seconds give or take they are defective. Solenoid function for proper specification for needed pressure to open the pilot valve, main control valve leakage test, as a last resort a pump flow test.

Source: www.hydraulicspneumatics.com