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Re: [Shop-talk] single vs. dual stage compressors

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Subject: Re: [Shop-talk] single vs. dual stage compressors
From: "Karl Vacek" <>
Date: Thu, 20 Nov 2008 22:23:42 -0600
Randall -

That's not quite right.  The die grinder needs its air supply at 90 PSI, but 
in a minute it will exhaust 4 CFM of free air, not 4 CFM of 90 PSI air or 28 
CFM of free air.  The drop in pressure across the tool is from the expansion 
of the compressed air, which gives off its energy as work in the tool, also 
cooling as it expands.

Another example:  A typical siphon spray gun like a Binks 7 gun runs about 7 
CFM, typically at anywhere from 40 to 60 PSI, maybe higher or lower than 
that depending on what you 're spraying.  A real 2-HP compressor will run it 
continuously till you run out of paint or can't hold the gun any longer.  A 
2-HP compressor will go on and off while you're spraying.


> But there is something to be said for not pumping a big tank up to 175 psi
> if you don't need it.  I just can't imagine not needing it.  Even a small
> die grinder typically needs at least 4 cfm @ 90 psi; which translates to
> some 28 scfm in compressor-speak.  And even if I could afford a 28 cfm
> compressor, I don't have enough electrical power to turn it!
> Randall 
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