[Shop-talk] single vs. dual stage compressors

[Randall]

> Those 
> Chinese guys are 
> obviously using a 7:1 compression ratio at 90 PSI, a little 
> low but pretty close.

Yup.  One atmosphere is about 14.7 psi, so 90 psig is 104.7 psia or 7.12
atmospheres.

> Gotta 
> say, though, I don't think anyof my old original Chicago 
> Pneumatic stuff 
> uses anything like that kind of air. 

Could be.  But a friend let me use his shop once to work on my motorhome,
and his fairly old Chicago Pneumatic die grinder kept his air compressor
pretty busy.  Dunno what it's specs were, but it was the typical 120 gallon,
2-stage, 3-phase setup normally seen in auto shops.  I didn't time it, but
I'd guess it ran at least 1/3 of the time, until I was done.  And I wasn't
even running the die grinder at full throttle much of the time.

> and you don't 
> usually keep them going for hours straight.  You're always 
> stopping to do 
> this or that every few minutes anyway.

Maybe you work faster than I do.  With both the die grinder (usually with a
wire brush mounted) and the blast cabinet, I mostly have to stop to wait for
the compressor to catch up.

> A "real" 2-HP compressor

My old compressor runs on an ordinary 110v outlet, of COURSE it's not really
2 hp (although I think the label on the side actually says 2.5hp <G>).  And
it was made in Minnesota (or at least by a company that was headquartered
there).

> Can we now change this into a Chinese tool-bashing thread ??   ;-)

Sorry, I calls em like I sees em.  It's the American companies that
pioneered lying about ratings.  Horsepower, watts, cfm are all clearly
defined concepts; until a marketing guy gets ahold of them.  Note that it
was the "Chinese guys" telling the truth ...

Randall