On Wed, 24 Dec 2003 19:50:30 -0600, Richard J Kinch wrote:
jim rozen writes:
Cubic feet per minute is only a time
rate of volume.

No, no, no, no, no. CFM in compressors refers to the flow rate OF THE
INPUT AIR AT ATMOSPHERIC PRESSURE.

That's right. When you see a compressor rated at say 10 CFM @ 90 PSI,
that means 10 CFM of *inlet* air compressed to 90 PSI. It does NOT mean
10 cubic feet of 90 PSI air. This should make sense when you notice that
a compressor may have several fairly similar CFM ratings given at several
different pressures. That's because the only differences are due to
differences in the pumping *efficiency* of the compressor at different
delivery pressures. It is still inhaling roughly the same amount of air per
stroke at the same strokes per minute, so it still has roughly the same
CFM rating whether that's given at a delivery pressure of 45 PSI, 90 PSI,
or 140 PSI. It just takes longer to initially pump up the tank to the higher
delivery pressures.

Gary