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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 13:04:11 -0600
The other side of that is that if you don't regularly need the higher 
pressure, 2-stage compressors are less efficient than single-stage.  You'lll 
get more air with the same actual horsepower from a single-stage compressor 
operating at 120 PSI maximum than a 2-stage at 175 PSI maximum, assuming 
you're only using maybe 90-100 PSI for your tools or whatever.

The idea of filling your tank more is great if you're doing something 
intermittently, but if you're using air pretty steadily the size of the tank 
is essentially meaningless.  If you want to do something requiring more air 
than your compressor puts out, you'll have to work a few minutes, then wait 
a few minutes while the compressor catches up.  If that's OK, then a 2-stage 
might be OK for you, giving you that high pressure if you ever need it.  But 
what are you going to use 175 PSI air for in a typical home shop ?

If you have a 2-stage with sufficient pumping capacity - a big enough 
compressor head and motor to keep up at 100% demand - and if you don't need 
high pressure most of the time, you can improve its efficiency a little by 
just setting the pressure switch lower.  There's no use in pumping up a tank 
of 175 PSI air if the highest pressure you usually use is 100 PSI, AS LONG 
AS you have sufficient compressor capacity.

And though 2-stage compressors are indeed more efficient at high pressures 
than single-stage ones, they're less efficient when compared to single-stage 
compressors in the working range of the single-stage unit.  So if you don't 
need high pressure ever, don't go 2-stage.  You'll get more air per dollar 
of purchase price and per dollar of running cost with a single-stage.

But nothing impresses the women like a 175 PSI compressor - it's so much 
more macho than a wimpy single-stage, so if you have to have one, then go 
for it   ;-)

Then there are horsepower ratings.  I hope Randall will expand on this 
because I really don't like thinking about electronics, but be aware that 
horsepower ratings are often a complete fairy tale, particularly in consumer 
brands.  I strictly look at voltage and amperage, and compare from there.


>> Whats the deal with single vs. dual stage compressors?
> The main thing is that 2-stage compressors are much more efficient at 
> higher
> pressures than single stage.  That means you can store almost twice as 
> much
> air in the same size tank.  No big deal if your compressor is big enough 
> to
> keep up with the load, but it can make a big difference if you have to run
> at least partially on air stored in the tank (which is usually the case).
> Randall
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