> Here's the best advice on compressors ( for home use) I've found-
> http://www.practicalmachinist.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=ge
> t_topic;f=8;t=000039;p=0
Not bad, but it contains at least one glaring omission of fact. It implies that
air tool CFM ratings can be directly compared with air compressor CFM ratings
with a 2:1 fudge factor for "underrating". That's simply not true. Every
compressor I've looked at, even the big professional models, are rated in CFM
_at the inlet_ (sometimes expressed as scfm). But air is compressible, meaning
that 1 CFM at the inlet produces much less air at the outlet (when it's under
pressure). So for example, an air compressor rated (accurately) at "14 cfm @ 90
psi" actually only produces approximately 2 CFM at the outlet. Of course, air
tools are also rated by CFM at their inlet, so again for example, an air tool
rated (accurately) at 4 CFM, needs a compressor rated for (at least) 28 CFM !
(for continuous operation).
Since a 28 CFM compressor is very expensive, but most tools require at least 4
cfm, the tank does become very important. In effect, the tank size determines
how long you can run the tool (with an undersized compressor) before running out
of air.
As far as "fraudulent" "consumer" air compressor ratings, there was a recent
lawsuit over this. I've already noticed the result : the advertised "hp" now
bears at least some resemblance to the real motor power. It's still a lousy way
to rate a compressor IMO, kind of like rating a car by how much gas it can burn.
A compressor that uses 2 hp to produce 10 cfm isn't any better than a compressor
that uses 1.5 hp to produce 10 cfm.
Randall
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