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No Bob, I've seen this before. The governor is telling the compressor to knock off, but because of a defect in the unloader mechanism, it doesn't. If there were no dryer in the system, then the system pressure WOULD go way up and lift the safety valve as you describe. But since there is a dryer, it responds as I described earlier, and constantly pressurizes and purges, dumping the output of the compressor right then and there.
speaking of cycling every 5 to 7 seconds... how fast is this engine running if the compressor discharges only once every 5 to 7 secs?... that's a slow air compressor rpm ;0)Originally Posted by JoeyB
To get that thing to cycle every 5-7 seconds would take one hell of a leak. I've never taken one of these apart to see exactly what happens in there, but I'm told Midland compressors have some little pin that pops out of place or something that kills the unload function. No Bob, I've seen this before. The governor is telling the compressor to knock off, but because of a defect in the unloader mechanism, it doesn't. If there were no dryer in the system, then the system pressure WOULD go way up and lift the safety valve as you describe. But since there is a dryer, it responds as I described earlier, and constantly pressurizes and purges, dumping the output of the compressor right then and there.
i think that the discharge air cannot be pumped out through the purge valve because the cut-off valve blocks that opening (compressor discharge to purge valve opening). if that connection were left open, your 30 psi of manifold boost pressure would move down the discharge line and out the purge valve as well.
and the cut-off valve is closed by UNL (unloader air) from the governor. and, seeing as how there's 140 psi in the tanks, i'll assume it is in the "unloaded" cycle.