> I thought the point of the air tank was to run it at a higher pressure
> than the tool required.
The air tank provides a buffer in effect, between the compressor that either
runs at full output or not at all, and the air tool that draws varying
amounts of air, almost certainly not exactly the compressor output.
> If the tank is at 180 psi and the tool runs at
> 90 psi, don't I effectively double the amount of available air.
You get some increase, since the air in the tank will expand as the pressure
goes down and provide additional air for a short time. However, if the air
tool consumption exceeds the compressor output, the pressure in the tank
will eventually bleed down and you'll have to stop and wait for the
compressor to catch up.
> In other
> words, if the compressor can deliver 50% of the CFM required by the tool
> but at twice the pressure, doesn't that mean it will keep up with
> the tool?
That's kind of a non-question, since if the compressor is able to deliver
50% of the CFM at twice the pressure, it can also deliver 100% of the CFM at
the pressure. The _intake_ volume of the compressor remains nearly constant
(it does fall off somewhat with increasing output pressure), so at best the
output volume is proportional to the output pressure.
It's worth commenting too that the tool's cfm consumption will usually rise
somewhat with increasing pressure. To get the full advantage of the high
pressure air in the tank, you need some sort of regulator between the tank
and the tool. But, regulators add their own complications and some of them
won't flow enough air for a high flow tool, so most people don't use them.
Randall
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