OK guys, I can't stand it any longer. The damn Sears compressor HAS to go. Damn that thing is loud. I really thought I would get use to it. Nope.
This is strictly for a home shop and am looking to run the normal air tools, plasma cutter and a sand blaster. It's the sand blaster that's the air hog. It wants 12 cfm at 60 psi. The Sears compressor laughed.
I've gone through the archives of this groups messages and am looking heavily at Quincy and Ingersoll-Rand, probably in the 5 HP variety.
My question: Can someone elaborate on the terms "single-stage" and "2-stage"?
Anyone need a very nice Kaeser 15hp rotary compressor? Ive got one for sale, So. Cal. $1800 OBO. Its an older compressor, but allegedly its been rebuilt not long ago.
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Gunner
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Two stage compressors do the job in two steps, and are more efficient when the use pressure is above about 75 psi. When a compressor is used at a compression ratio above five or six to one in each stage the oils can start to combust from the heat. Also volumetric efficiency is lost due to the squish space at top dead centre containing a lager percentage of the air compressed. When looking for a compressor ignore the words "horse power". It is the most over-hyped term in the marketing of air compressors. For 120v 15 amp receptacles the maximum continuous circuit loading by code is 13 amps. This works out to 1.5 horse power at the motor shaft. The spec you are looking for is Standard Cubic Feet per Minute (SCFM) at the pressure you want. I would recommend a two stage compressor rated at 12 cfm at 120 psi. This unit will require a 15-20 amp 220 volt circuit.
I ended up with a used 1946 vintage two stage with a newer true 5 HP motor for $300. It catches up with my glass bead booth and I can paint all day long if I wanted. I did spend about $100 more for the magnetic switch with thermal protection. The guy was selling it cause it would not keep up so he bought a 7.5hp. I had to tighten the belts and the 4 bolts that hold the transfer pipes on the head to make it work fine (the bolts were finger loose).
I had a one of those cheapy 5 hp ones and I just waited for a real one to show up in the paper which happens about 3 times a year in my area.
Check your paper and look up a used machinery sales company. You may save some bucks.
It seems to me that a two stage is the better choice even if you are using air below 75psi. The tool gets 75psi, but you will probably run the compressor at a considerably higher pressure with a regulator in between it and the tool, which means a two stage will run more efficiently (I think).
Jim, given your complaint that the Sears is LOUD, another benefit of a two stage is that is is quieter than a single stage. You can also slow an oversized compressor down and make it even quieter.
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