One of the most common indicators of inter-stage valve issues is a relief valve on one of the stages discharging. This indicates that either; one of the inter-stage valves is not operating properly or the valves are worn, and the unit is likely due for a valve service at minimum. The first thing to determine is if the relief valve has gone bad or it is an issue of high inter-stage pressure. You need to determine which relief valve is leaking first and determine which stage it belongs to. Next you would have to confirm if that stage is operating at the proper pressure depending on what your final outlet pressure is.
If the pressure is in its normal operating range or relatively near it, then you may be looking at a worn relief valve. If the pressure is well above its standard operating pressure, then that is an indicator that the stage after it most likely has worn valves. You would then want to approach changing the valves BUT note that all the inter-stage valves should be changed at the same time. Changing one stage while not changing the others will cause the other stages, and potentially the rings, to wear at an accelerated pace and you will have to change them shortly anyway. The only exemption to this would be if the valves are relatively new; they are either faulty valves and need to be replaced or they were not seated properly so they need to be retightened.
However, this all also depends on the unit and which stage it is. Some units could be experiencing an issue that appears to be like bad valves, but it could be caused by an issue with pressure flowing back through the ACD or Automatic Condensate Drain (if it has one). The ACD is draining the inter-stage and final oil/water separators at preset intervals and on start-up/shut down. Many ACDs are set up to rely on control pressure from one stage maintain another. In those cases, an issue with the ACD may cause higher stage pressure to flow back through the ACD into a lower stage. If your unit has a substantial amount of hours, say above 1000-2000, or has not been serviced for years (5 or more depending on use and location), it may simply be due for a valve job and it is usually a good idea to service the ACD at the same time.
If you're looking for valves you can check out our selection of Bauer Compressor Valves here.
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