Buying a used air compressor: tips?

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On 2/10/2011 10:12 AM, Vic Smith wrote:

I think Clare had the best idea about changing your single 115 line to a 220-240 line. Although I don't know if that calls for a third wire or if you can use the ground as a neutral and drive a ground rod in at the garage. If possible, that is your best bet for now and down the road. Double your capacity through the same wires.
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On Fri, 11 Feb 2011 11:11:04 -0500, Tony Miklos

L1 and L2 and ground with no neutral as you do not need any 110 volt capability. No ground rod issues ar anything, assuming you have a grounded cable now. You do need to mark the white wire red, or pigtail a red wire to it to identify the former neutral wire as a live conductor.
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On 2/11/2011 12:25 PM, snipped-for-privacy@snyder.on.ca wrote:

That doesn't sound so great anymore, power for the compressor but no 120 for everything else. I'd be checking to see if the wire can be pulled or not through the old conduit. If so then install a legal/code/safe run with 240 and a neutral. But if he just wants to inflate tires why bother. On the other hand he mentions sandblasting, either a tiny blaster, way too much patience, or go with the 240.
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On 2/10/2011 10:12 AM, Vic Smith wrote:

Oh my more setbacks. Trying to compare my 25+ year old 1hp Sears compressor to the one in the link. My 1 horsepower puts out 5.8 SCFM @ 90PSI. Yours is rated different, it puts out 5.2 CFM @ 90PSI. So we need to convert SCFM to CFM or vise versa. I want to see how my old 1HP compares to the new 2HP.
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wrote:

I can think of another. It possible that there is some design difference in how the motor is wound or some other aspect that makes it more difficult for it to stall if someone shuts it off and then immediately back on when it's pumping under high pressure.
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Ashton Crusher wrote:

Far as I know they all unload when the motor stops I wouldn't bet on starting against high head pressure.
I think the answer is closer to what clare wrote. In looking around, the motors I saw on compressors were capacitor start, capacitor run. Those motors, in general, have relatively high starting torque and relatively low starting current for that torque. I have seen no reason to believe "special compressor motors" are anything but standard cap start, cap run motors.
The problem I have is Jon's 3HP SPL motor. It is a scam rating. Just like the scam ratings that resulted in the class action lawsuit, which the manufacturers settled. If Jon knew it was not a real number then why post it? (And then there was Jon's 2.3HP miscalculated value.)
A scam "peak" 3HP motor has a peak (near stall) torque that is equal to the normal running torque of a 3HP motor. It is not the starting torque of a 3HP motor.
For many of its smaller compressors, Grainger gives both the scam "peak" HP (competitive with Jon's scam rating) and a real HP.
I haven't seen any reason to believe that the "real" HP is not the appropriate rating. Because there are plenty of scam ratings, you can't compare compressors based on HP rating (as many people here have said). Even with real HP ratings you need to compare the air you need with what a compressor provides (also as many people here have said).
============This is similar to joule ratings on surge suppressors. In that case there is not a defined way to measure the joule rating. So some manufacturers use deceptive ratings. As a result, some major manufacturers no longer give a joule rating.
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On 02/08/2011 03:54 PM, Jon Danniken wrote:

So what would be the rating of your motor, were it rated the same way as other electric motors?
You don't know and I don't, either, that's the problem.
nate
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On Mon, 07 Feb 2011 10:56:41 -0500, snipped-for-privacy@aol.com wrote:

I asked about how to choose a reliable used compressor, not how to select an appropriate one, but your comment is constructive, and deserves a response.
I will be using the compressor for small construction and woodworking projects. The tools I'll probably use most will be a utility stapler and a finish nailer. I might do some painting, but that will so rare that I wouldn't want to get a larger (costlier, heavier, more power hungry) compressor to keep up with a paint gun.
Last time I owned a compressor it was a dual-tank Emglo. I think it was rated at 1 1/2 HP and drew about 14 amps. I'll be perfectly happy to get something similar now, although I'd prefer one that's less noisy. I understand that the lubricated models make less noise.
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wrote:

Matching a compressor to the job is just a good idea. One that is running 100% of the time will wear out a lot faster. You may need more than one compressor.
Steve
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You can get some good deals at pawn shops. Buy a brand name, and buy one that looks clean, that's about all I can suggest. If you're just going to use it for nailers, etc, you don't need much, and as long as it will build up pressure, and doesn't leak, there isn't much else. Take a bottle of Windex, and pressure it up, and test for leaks. Open up the bleeder valve on the bottom once it's pressured up, and see if any water comes out. If it does, pass. It means the owner hasn't bled it regularly, and there will be water and rust inside the tank.
Steve
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On 2/7/2011 1:14 AM, Jonathan Sachs wrote:

Do not buy an "oilless" piece of crap. Go for a belt driven compressor that does require oil.
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