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Old 03-20-2011, 08:23 PM   #1
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Help assembling compressor


A friend of mine gave me a compressor and motor in trade for a sewing machine I'd tuned up, and now I want to assemble this into something I can use occasionally with air tools. I'd also like to use it to blow out some hoses on our property in late Fall, so that we can leave them out there for the winter without fear of freeze-up problems. I'm NOT looking to use it for painting or anything terribly fancy like that.

I'm good with plumbing and electricity in general (I own a boat, which means I pretty much HAVE to be!). But I've never done much with compressors.

The compressor itself is large -- it looks like the kind that might be used on one of those 75 or 100-gallon units -- but I'll be using it with something more like 5 gallon storage. It's got a 10in diam drive pulley. It appears that the drive belt is supposed to be a ribbed thing like the serpentine belt in a car. 6 ribs, 1/2" wide. Not clear to me where I should get such a belt, but I'm looking at the Gates catalog.

Anyhow, my question is "what else do I need, and in what order?" I plan to mount the compressor, tank, and electric motor on a piece of 3/4 plywood (painted), with caster wheels. That part's easy. If I understand it right, I should take the output of the compressor and plumb it to a tee-fitting into the tank. The other side of the tee-fitting goes to a pressure-sensitive switch: turns on at 120, off at 150psi, or something in that general range. If I get a four-port switch, I take one of the other ports and plumb it to a filter/regulator unit, and put an pressure-release-safety valve into a third port. The harbor freight filter-regulator I'm looking at has a pressure gauge, so the fourth port gets plugged, I suppose.

1. Am I getting the right idea so far?

2. Should all this be "hard" plumbing, i.e., made up from brass nipples, etc., or should I use hose between the compressor and the rest of the air-handling stuff, which can then be mounted to the plywood in some secure way?

3. After the filter-regulator, am I right in thinking that the "output" of the compressor should be a quick-coupler, of the female variety?

4. The compressor itself has an oil sump, or at least, it has two plugs near the bottom, one very low, which looks like an oil drain, and one higher up, that looks like a fill. How do I know how full it should be?

5. I see that Harbor Freight sells compressor oil; is there anything special about it? Would ANY 30-wt oil do the job?

6. After all the filtering and pressure reduction, I have a hose to hook up to various tools. Am I right in thinking that a typical tool (like a "blow gun" or an air-impact-wrench) has a male quick-connect on it, while the hose from the compressor to the tool has a male quick-connect at the compressor end, and a female quick-connect at the tool end?

7. K-mart sells a Craftsman 5gallon tank (with a pressure-relief valve) (http://www.kmart.com/shc/s/p_10151_1...649836611#desc), but I don't see a tank-drain. Is a tank-drain essential for someone who uses a compressor only occasionally?

Thanks in advance for any suggestions you can give.

--John

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Old 03-21-2011, 07:14 AM   #2
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Help assembling compressor


Have you ever played with "Lego's" or "Lincoln Logs" that someone took some pieces away? This is pretty much what you have there, a mess of parts, and not all that you need. YOU stated that this unit is large, so we may not be talking about a light-weight unit here. You will need to know what voltage the motor of the unit needs to run, this IMO will determine as to whether or not you will be able to build a portable compressor. Is this a single or double cylinder compressor? This determines if it is a single stage/one cylinder, single stage/two cylinder, or a double-stage twin cylinder unit. Are you planning on mounting the motor/compressor unit onto the plywood or the old tank? Plywood is not a good idea IMO. After the compressed air leaves the compressor you will need to use, preferably, copper tubing from the compressor head to the fitting on the tank. This line will get very hot, and the fitting on the tank WILL HAVE a check-valve built into it. You should find a way to mount your pressure cut-in/cut-out switch and pressure regulator somewhere else. The pulsating pressure/volume of the line from the compressor head will beat these to death most of the time. Go look at a similar unit at some store and examine it well. There are so many components to a good air compressor system.

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Old 03-21-2011, 07:52 AM   #3
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Help assembling compressor


Thanks very much, Thurman, for your comments. Here are some answers.

Voltage: it's a 110V universal motor; I don't have a lot of worries about the electric part of the thing, which is why I didn't ask about it.

Is this a single or double cylinder compressor?: It looks to me as if it's a good fraction of a 2-cylinder motor, but without the spark plugs. (To put it more precisely, it's kind of rectangular, about 11" tall, 8" wide, and 4.5" deep. THe top half looks like two adjacent cylinders surrounded by fins. The bottom half looks like a crankcase. When I spin the drive wheel, air comes out of a 3/NPT male fitting at the top, one "gust" per 180 degrees of rotation.) So my guess is "2 cylinder, single stage."

Are you planning on mounting the motor/compressor unit onto the plywood or the old tank?: I don't have a tank yet. I'm thinking about buying one. The ones I've looked at don't have an obvious place for mounting a motor or compressor, hence my thought of a plywood base.

Plywood is not a good idea IMO.: Can you explain why, so I can make an informed choice?

...use... copper tubing from the compressor head to the fitting on the tank: Thanks. That's very helpful. I suppose that if the tank and compressor are NOT mounted together, that tubing may have to absorb some vibration. Perhaps I should make sure that it's not a hard, short connection, and be sure to mount the tank on some soft rubber mounts.

This line will get very hot, and the fitting on the tank WILL HAVE a check-valve built into it.: Really? It doesn't appear to be the case for the Harbor Freight or Craftsman tanks I've looked at. Is this a case of "SHOULD HAVE", so that even if they don't have one, I should put one in?

You should find a way to mount your pressure cut-in/cut-out switch and pressure regulator somewhere else.: Thanks. That's great. Would "Downstream from the tank, after a length of rubber hose" be appropriate?

Go look at a similar unit at some store and examine it well. : I'll do so, but the difficulty of reverse-engineering from an existing model is that I cannot always tell why certain decisions were made (i.e., "Is that made of copper tube because it's a particularly good material choice, or because it's cheaper?" and "Is the check valve between the tank and regulator because that's where it should be, or because there was room there and it made things more compact?") That's why it's so helpful to have folks who know something about the subject to ask questions of.

Thanks again for your comments!

-John
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Old 03-22-2011, 07:15 AM   #4
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Help assembling compressor


As one of the insurance commercials that I have heard on the radio goes, "you're going to have to trust me on this one". (Or not, which is up to you, as this is the internet afterall.) Anyway, assembling an air compressor is not rocket science, but given that you need a tank, pressure switch, check valve, and gauge, as well as some copper tubing, fittings, etc., you would probably be money ahead to sell what you have to your local scrap dealer, and buy a new compressor. Right now, as an example, one of my air compressors, which is over 30 years old, but runs great, has a hole in the tank, so I won't use it. It's a quality brand that I bought new, and have kept it well maintained, so I want to simply replace the tank, but a new tank from WWG is almost $40 more than a comparable sized air compressor from TSC; not near the quality of mine, but I sure as heck am having a hard time justifying spending another $40 to repair something that I have versus simply replacing it.
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Old 03-26-2011, 09:54 AM   #5
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Help assembling compressor


Quote:
Originally Posted by DexterII View Post
As one of the insurance commercials that I have heard on the radio goes, "you're going to have to trust me on this one". (Or not, which is up to you, as this is the internet afterall.) Anyway, assembling an air compressor is not rocket science, but given that you need a tank, pressure switch, check valve, and gauge, as well as some copper tubing, fittings, etc., you would probably be money ahead to sell what you have to your local scrap dealer, and buy a new compressor. Right now, as an example, one of my air compressors, which is over 30 years old, but runs great, has a hole in the tank, so I won't use it. It's a quality brand that I bought new, and have kept it well maintained, so I want to simply replace the tank, but a new tank from WWG is almost $40 more than a comparable sized air compressor from TSC; not near the quality of mine, but I sure as heck am having a hard time justifying spending another $40 to repair something that I have versus simply replacing it.
Thanks, Dexter, for the advice. I've been sneaking up on that idea myself. There's the potential satisfaction of doing it myself, and (on the other side), the potential annoyance, not to mention the delay in getting things done. I'll have to muse on this a bit.

--John
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Old 03-27-2011, 10:07 AM   #6
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Help assembling compressor


So much stuff yet to cover, but let's see if we can help: IF there are two cylinders with this compressor, and they are the same size: then it is a two-cylinder single-stage compressor. Meaning both cylinders compress air at the same rate, sort of like having two compressors. BUT IF they cylinders are of different internal dimensions, then this will be a two-cylinder, two-stage compressor. Meaning that the larger cylinder will compress the air to app. 40#, then push the air into the smaller cylinder for final compression around 120# or so. Mounting this compressor unit to plywood means the plywood will be absorbing a lot of vibration with will tend to continue to loosen the fastening method used. Copper tube is generally used for the line from the compressor to the tank for it's semi-rigidity, and it tends to dissipate heat very well. You will see some compressor's with fins around this line to help dissipate heat. Trust me, ALL compressors you look at in any store, commercially built, will have a built-in check valve where the line connects to the tank. These often appear to be just a brass fitting, but they are check valves in reality. IF not for the check valve, the air released from the compressor would try to flow back to the compressor and when a higher compression rate is achieved the compressor will start to "dead-head". Most "cut-in/cut-out" switches and pressure regulators are mounted directly to the fitting that is mounted to the tank, it's just that the fitting is made so that the compressed air is forced into the tank first, then the switches to prevent the pulsating effect of air being compressed. AND: Read Dexter II's posting very well, it's good advice.

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