CFM vs SCFM?

Looking at some used and new air compressors, how do I compare SCFM to CFM?
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SCFM is standard cubic feet per minute. It is at 68 degrees, 37% humidity. It is usually used at the airflow into the compressor. Some use CFM for the output. They can jiggle the temperature and humidity to make the numbers appear a bit better too. SCFM sounds more honest.
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On 10/9/2011 9:12 PM, Ed Pawlowski wrote:

The above is more like a definition of NTP (normal temperature/pressure I think--unfortunately, there are also multiple definitions for it as well as the multiple ways of measuring/reporting compressor performance.
To really have any idea, one needs to be able to find out the reference conditions used even w/ SCFM labeling. :( The better the manufacturer (read expensive like Ingersoll-Rand/Quincy/other industrial guys) the more likely the results are trustworthy in comparison to the low-cost consumer-market thingies...
But the CFM ratings generally are outputs--they'll be something like x cfm @ y psi so that the pressure is given. Temperature generally isn't; it's just whatever the output temperature of the air coming out the the compressor is after the compressive cycle. So there's still that slight variable even then altho unless the testing conditions are really seriously manipulated one would presume that roughly the same size compressors will have approximately same temperature rises and they won't go to the trouble to run the test chamber input air from a grossly refrigerated source to lower the temperatures artificially.
A reference to a bunch of various definitions that's kinda' handy...
<http://www.engineeringtoolbox.com/rating-air-compressors-d_848.html <http://www.engineeringtoolbox.com/stp-standard-ntp-normal-air-d_772.html
--
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On Sun, 09 Oct 2011 20:47:39 -0400, Tony Miklos

Just don't forget to double the about of cfm/scfm the tool says it needs-- and cut the cfm/scfm the compressor says it produces in half. You can't go wrong that way.
They are ballpark and infinitely fudge-able numbers.
Jim
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