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Hi this compressor is supposed to deliver 7.8 cfm fad but is not keepin up with a tool that is rated needing 6cm so it appears that my machine is not pumping enough air. Everything else seems to work fine it starts, gets upto its cutoff pressure but presumably it is not pumping quick enough. If it was a car engine I would do a compression check to see if it was the piston rings or valves that are the problem but how do I do that on a compresssor. The pump is a twin cylinder single stage 3 hp item. any help would be appreciated. Many thanks Steve

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The best way to determine how the compressor is doing is with a pump up test. Time how long it takes the compressor to pump up from one pressure to another. If you know the tank size, you can then compute the air delivery of the compressor:
CFM=(Pressure Change / 14.5) x (tank size in gallons / 7.48) x (60 / time in seconds)
I'd recommend start timing about 40 or 50 PSI and pump up to shutoff.
If your compressor has no aftercooler (it probably doesn't) this should read a bit higher than your 7.8 CFM FAD because the air will be hot, but it will get you in the ballpark.
If compressor seems OK, tool could be worn or fed too high a pressure (if you put 120 PSI to a tool, it will use quite a bit more air than it is rated for - they are usually rated for about 90). If your compressor maintains pressure at 95 or 100, but doesn't gain ground, everything is probably OK. I'd just add a pressure regulator to maintain 85 or 90 to the tool in that case.

Posted on Apr 02, 2011

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Leave those high air volume air tools to shops that are so equipped to use, or invest if you must.

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