Gary Coffman wrote:

Yes it makes sense.
Go he http://air.ingersoll-rand.com/CMP/sa...vertlevel3.htm
and then try to explain why the CFM ratings of these compressors don't
markedly change over a 75 to 175 PSI range.

For example, the IR 5 hp dual stage I have is rated at 14.9 CFM @75 PSI,
14.8 CFM @125 PSI, and 14.7 CFM @175 PSI. Same compressor, same
displacement, same speed, and nearly the same CFM over a pressure range
of more than 2:1. If we were to believe they're talking about CFM of
pressurized air, the gas law tells us we would see more than a 2:1 change
in CFM with a 2:1 change in pressure. But we don't. The only way we can
see the numbers they publish is if they're referring to CFM at 1 standard
pressure.

I don't see it that way. If the spec isn't about CFM of pressurized air, then
why would the numbers differ at all for different output pressure? And why
quote CFM into different pressures? Why quote pressures at all?

Those numbers make sense to me as CFM of pressurized air. If you need more
volume than 14 cfm, you have to use a regulator to expand the air downstream
to get more flow. If you set your pressure switch to pump your air tank up
to 175 psi, then you have the headroom necessary to regulate it back down to
your desired end pressure but get quite a bit more volume.

Those specs relate as I see it to the pump and motor. If you run a pump at
a certain speed it is going to put out a fairly limited range of air flows
depending on its output pressure. A single stage pump's output flow will
drop much more markedly with output pressure than a two stage pump. An
ideal pump would have (to use an electrical analog) zero output impedance
so it would put out the same flow regardless of pressure.

It sounds like you have a pretty good compressor.

Grant Erwin