In article , Richard J Kinch wrote:
Gary Hallenbeck writes:
I DO understand what CFM and SCFM mean. I worked with compressor
specification and air system analysis ,around the worl, for 25 years.
... A CFM is just what it says it is. One Cubic Foot per
Minute at any temperature, pressure or humidity.

Your (former) employer disagrees. If you look at what Ingersoll-Rand
says in "Compressed Air Basics":
http://air.irco.com/asg/air_system_info/basic.asp
you'll see that CFM there refers to cubic feet of free air per minute.
I defy you to show me elsewhere on ingersoll-rand.com that says
otherwise.

Richard is saying that CFM is at 1 atm, right? so an ideal compressor
would take in 'X' CFM/min and output that same amount, regardless of the
output pressure. does this make sense to anyone else? the discussions
of altitude and other losses seem to obscure this, imho (as does the
fact that no ideal compressor exists ;-).

also, i gather that SCFM is simply corrected for moisture content, and
some other factors that would not impact comparison of honest ratings?

now, the "power" required for a 90psi vs 175 psi output pressure makes
for real world examples, especially when you leave the "ideal" realm.
often said by the professor, ...an exercise for the student... --Loren

Read the Grainger catalog section on "Guide to Air Compressors". You
will find this definition: "FREE AIR: The actual volume (CFM) of air
produced by the compressor pump at rated pressure(s)."