Roll your own air compressor?

Hi,
Some time ago, on ebay, I bought a new air compressor pump like the one shown here:
http://www.grainger.com/Grainger/items/2Z498
Although the pump has now been discontinued the site shows the technical specs for it.
In the side of the compressor head are two threaded holes. One appears to be 5/8" or perhaps 9/16" and the other, is 3/8".
According to the grainger site the outlet is the 3/8" hole. I have a couple of other compressors and they have a single outlet hole and it appears to be larger size.
Can somebody help me understand what both these outlets (assuming they're both outlets) are for? I originally hoped the compressor would provide enough air to supply a TD Cutmaster 51 plasma cutter. It looks like it is not capable of doing that. Nevertheless, I would like to assemble a small portable, light weight compressor with it. I have a lightweight portable, but the buzzing noise drives me crazy.
If somebody could point me to a schematic of the necessary safety components I will appreciate it.
Thanks,
V
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wrote:

Turn ot over by hand and put tyour finger over the holes. See which one blows and which one draws. The inlet MUST be larger than the outlet. For a 2.5 cfm compressor 3/8" outlet does not sound terribly small. Some have 2 outlets - one for the air to the tank and one to the unloader - so that's a possibility too. (then it would have a built-in air intake filter/silencer)
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Vernon wrote:

One hole is an inlet the other the compressed air outlet.
That unit looks a lot like the ones used on many of the old milk cooler units.
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[runs downstairs to take a look]
I have a plug in the small hole and the outlet tee in the larger one. One leg of the tee has a water heater pressure relief, the other goes to a Load Genie check plus relief valve and then the tank. I think the smaller hole might be for an unloader piped to the pressure switch, but that compressor's pressure switch was meant for a well and doesn't have the air valve. Northern sells switches that do, I installed one on the salvaged/rebuilt Husky air compressor which has a plain check valve leading into the tank.
The Load Genie jams if the inlet tube isn't well aligned. It doesn't leak between uses, unlike the pressure relief plumbing on the Husky
I put a 1/2 HP motor with a 3.5" pulley on mine and set the limit to around 80PSI. That seems a good compromise between enough volume and enough pressure for inflating tires and cleaning carburetors etc. It is NOT enough to run the plasma cutter and cost me burned-up consumables when I tried. It's marginal for air tools but most of my weld grinders are electric.
It is however enough to sand-blast a whole bumper with a pressure- feed, canister gun from Sears (long ago) if I connect a larger tank to even out the pressure variations while I'm refilling the gun.
I bought the vacuum head attachment and installed it with a street elbow in the inlet hole, facing down to help exclude dirt. I pulled it off coincidentally this morning to clean the filter after 5 years. The filter was barely discolored and the small amount of sawdust or whatever that was sucked in had stuck to the inside wall opposite the street elbow.
jsw
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Jim. If I'm not mistaken it was only today, and precisely the result of me reading one of your discussions about your compressor that got me interested in cobbling something together. I found your comments (if indeed it was you!) by searching google for the compressor model number. Your post was in response to somebody saying that a small compressor was "useless in the real world" or words to that effect.
Small world.
V
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That's a reminder to be careful what we write.
Somewhere I saw a chart of pressure vs pulley size for the 2Z498 and a 1/2HP motor, and copied it onto the tank. The 3.5" pulley on it now is good for 100PSI. The motor draws about its full current as the pressure nears 100, but it doesn't overheat. You may be able to supply the plasma cutter with a 1-1/2HP motor running that compressor, and the largest pulley that the motor tolerates, if you set the pressure switch to turn on just above 75PSI and off as close above that as it will go. One spring is for set point, the other is the differential between On and Off.
I think the Load Genie might not be the lowest restriction check valve you could find. It needs a pressure differential to stay open. When the motor and air flow stop the valve slides back to seal the tank and open the line to the compressor head.
The volume vs pressure relationship falls off at some point that depends on the dead space in the head. You really have to try different motor pulleys and measure the current.
jsw It's 2 AM here, goodnight
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wrote:

Ayup..pretty much, unless your world only has a lot of air mattresses and beach balls and really small spray rigs.
Gunner
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    If there is no foam rubber intake filter on top of the head, I suspect that the larger hole is for an intake filter cartridge to screw into. You need a larger diameter at a lower pressure to move the same amount of air.

    :-)
    What about a tank? You'll need that to make for reasonably stable airflow instead of a train of pulses as the piston moves up. One of those, a motor (1 HP to 1-1/2 HP according to the web page), compressor itself, a belt and pulley (the flywheel will be the other pulley I suspect). Hmm the web page mentions the flywheel in the description, but it does not show in the photo -- do you have a flywheel with yours?
    Anyway, you'll probably want some wheels and a stand to make it easy to move with all of that. But it will be quiet relative to the buzz box which you have.

    Well ... you'll need a regulator, a pressure relief valve (sized mostly by the specs for the tank -- but not much more than 125 PSI for a single stage. And -- you will need a pressure operated switch to start and stop the motor -- and to vent the line between the compressor output and the tank input so the motor does not have to fight back pressure to start. The tank should be ASME rated for more than the pressure which you expect to develop.
    By the time you are through, you will have something quite similar to the old Craftsman one which I picked up at an estate sale a few years ago. I forget the actual airflow rating, but I think that it is a bit more than this pump is rated for.
    Good Luck,         DoN.
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The air intake on my 2Z498 is the felt-filled rectangular opening in the top center of the head.

I mounted it on a 12 gallon tank with 2 wheels, 2 feet and a handle from Grainger. Larger or smaller would work too, but 12 gallons has been a good size. While the tank was open I rinsed it with LPS-3 to keep down the rust. 35 years later the drained water is still white (dissolved air), not rusty.
I added an extra air outlet upstream of the regulator and use it more often than the regulated one.
Don't forget to make a belt guard.
jsw
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Don (and everybody)

The top of the compressor head does has a little screened area. It
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wrote:

It will work with a bigger than you would expect tank..but only for a few minutes or so,until the tank can no longer deliver5.8cfm at 75 lbs
Ive got a Miller 2050, and cant run it off of any of my small portables. Simply isnt enough volume in the tanks for anything other than a foot or so of cut. And the build back up time..sheesh.
So I use it off my big compressor and have a 150' of 1/2" hose. Which works ok..but the hose really should be bigger.
Gunner
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I strongly discourage you from wasting your time on this undersized head. However, it is easy to make RYO compressor. You need a motor, a pressure switch, a tank, air intake filter, piping, and a safety valve in the tank. The time and expense of parts will most likely make this uneconomical. Much easier to find a used working compressor for not too much.
i
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wrote:

At 2.9 CFM..its a rathe small compressor..and is highly unlikely to do the job. Period. End program. Full Stop.
Now..you can put a faster motor on it...3600 RPM..and if the compressor hold up.....it might come close to what you need. Or it will grenade itself before long.
Small and portable in relation to a large plasma cutter..simply isnt in the cards. Medium sized and sorta heavy..that will work.
Or get a tank of Nitrogen (hell..steal one off a telephone pole after a hard rainy week (just kidding!) and use it. And nitrogen is really cheap
Gunner
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wrote the following:

Grenade is right. <shudder> Wouldn't a larger head be better? 18SCFM, $149 http://fwd4.me/T5c 6.5hp gas engine, $129 http://fwd4.me/T5h Or a cheap, used 5hp electric motor could power it nicely.

Nitrogen bottle on a phone pole? What's that all about?
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Larry Jaques wrote:

The old, lead jacketed cable would pinhole. The bundles of wire were wrapped in paper to protect them from the heat while the lead was soldered along the seam, or during repairs. Water would get in the pinholes and be adsorbed into the paper. That cause problems for the phone lines. They would use the nitrogen bottles to pressurize the cable to prevent water from getting in, and to use an ultrasonic sniffer to find the pinholes.
There is very little leaded cable left in use. It was replaced by flooded cable, filled with a gel to allow direct burial or aerial use.
I haven't seen a nitrogen bottle chained to a pole in over 20 years. I used to see them fairly often. Sometimes two or three chained to a single pole, when they had a major problem, or they were building out a new section and the ports weren't sealed.
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On Wed, 16 Jun 2010 11:59:29 -0400, "Michael A. Terrell"

Still see them here in the rural areas of California, where wire has been hanging for many many years in wind and Heat.
Gunner
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Gunner Asch wrote:

They moved to mostly underground & fiber optics around here, starting about 20 years ago. I was told it was a constant battle to seal the pinholes, and a lot of new homes and business were being built. Since they had to add new circuits, they just wrecked out the old stuff.
They started moving to underground copper in downtown Middletown Ohio in the '70s. Looking at aerial maps of those areas toda show no overhead utilities.
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I've seen nitrogen bottles in New York City as recently as May 2010. No doubt they still have a lot of the old cable.
Joe Gwinn
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Joseph Gwinn wrote:

I was told that high lightning areas got more pinholes. That, and lots of areas of Florida get enough salt to corrode exposed metals. I talked to the Centurylink crew who is trying to track down an intermittent in my phone service a few days ago. He said there are a few very short runs of lead left in this service area, but they no longer do the soldered repairs. Instead, they use the same flooded splice housing made for plastic cables. I got the impression that they can't wait to see those few pieces of lead go away. Some early plastic cable wasn't flooded, and can be pressurized. from what I've been told, they do it at the switch centers, except when a line is damaged and can't maintain pressure.
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On Wed, 16 Jun 2010 08:38:44 -0700, Larry Jaques

Hummm? You have never seen the black pressure cylinders standing next to telephone poles in your area? Thats pretty common in some places. Generally the phone companies use them for getting rid of water in cable splices and wet wires. They "inject" nitrogen into a cable and it evaporates the water that has seeped in and is making a noisy connection. We see them regularly here in the West.
http://answers.google.com/answers/threadview?id09530
Gunner
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