> I'm not sure how to translate CFM at one PSI to CFM at another PSI
> (maybe it's exponential by PSI or something), but it would seem that if
> the tool's requirement is 5 CFM @ 90 PSI and my compressor is rated at
> an air delivery rate of 19.5 CFM at 100 PSI, I should have enough
> compressor capacity to run about 4 of those tools. The PSI is about the
> same, but the compressor delivers almost 4 times the tool's required CFM
> at the required PSI.
>
> Yes/No?
No.
The "5 cfm @ 90 psi" is fairly straightforward, the tool operates on 90 psi
supplied (or more) and passes 5 cubic feet of compressed air per minute when
supplied with 90 psi. It will likely use somewhat more (but not a lot more)
when supplied at a higher pressure.
The tricky part is the "19.5 cfm @ 100 psi". As I've tried to explain,
compressor manufacturers never, ever, use actual cfm even when they say they
do. They always use "standard" cubic feet, which means the volume the air
would occupy after it was allowed to expand back to room temperature and
pressure. Air comes pretty close to obeying the "ideal gas" laws (at these
temperatures and pressures), so at a constant temperature, pressure times
volume remains a constant. Double the pressure gets you half the volume.
Another slightly tricky part is that we are talking about "gauge" pressures
here, meaning relative to atmospheric pressure rather than absolute.
So, if you start with a cubic foot of room pressure air, and compress it to
15 psi (roughly twice room pressure), it's only 1/2 cubic foot. Carry that
a little farther, and you'll hopefully see that "19.5 scfm @ 100 psi" really
means "2.5 cfm @ 100 psi" meaning that big, honkin air compressor won't keep
up ...
Of course, I've ignored lots of smaller effects, but that's the gist of it.
Randall
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