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Old 04-10-2006, 03:28 PM
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Figuring Air Compresssor CFM

I "inherited" an old stand up compressor with no air output ratings on it whatsoever. It is a single stage, maybe 30 gallon tank. Name brand is Gilbarco. The tag on the motor states its rpm and a tag on the pump has the bore and stroke. Is figuring the CFM as simple as bore x stroke x rpm(corrected for pully ratio)? [(pi x r^2) x stroke] x rpm


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Old 04-10-2006, 04:22 PM
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You may have as much luck just doing an estimate from comparing similar compressors..Gilbarco is a service station equipment supplier and has a lot of stuff under its name made by other vendors..

I have tried most all of it and now do what is known to work..
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Old 04-10-2006, 08:35 PM
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It would be simple to just use displacement X pump RPM if the the pump were 100% efficient but that is not the case so anything short of using a flow meter would just be a crap shoot.
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Old 04-11-2006, 02:08 PM
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One way to compare is to find one with the same size tank that you know
the cfm of. Then measure the time it takes for that one to pump up to
say 100 psi. then compare to yours.
Maybe if you time yours and post it here, someone with that size tank and
similar pump-up time can tell you their cfm spec, you'll get close to
An old worn out compressor can run twice as long as a new one,
so cylinder volume by rpm won't really tell you.
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