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Air compressor project

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  • Air compressor project

    I built an air compressor back in the early 1980's. Back then there were no cheap imports and compressors were very expensive. I bought a quality single cylinder air pump and used a discarded water pressure tank as the receiver. The motor was a General Electric 1/2 hp refrigeration duty motor rated for 100 percent 24/7 duty cycle.

    It has served well over the years. It doesn't have a lot of CFM capacity but it can run all day without danger of smoking. The motor is twice the size of today's 1/2 hp motors and doesn't become more than slightly warm to the touch in continuous operation.

    A while ago I decided to take it out of primary service because the receiver is getting too old to be safe. I set the maximum pressure to 45 psi and use it for blow-off air in the shop. I have another smaller compressor that has been supplying shop air but it is noisy and can't take 100% duty cycle.

    Now for the "rest of the story"...

    I have been keeping an eye open for something to use as an air tank. The best I could come up with is an old 100 lb propane tank I have. Yesterday my daughter (they are visiting) drove to the transfer station (new name for dump) to dispose some trash for a friend . Just as they arrived they had a flat tire and called for help. My son-in-law and I headed out to the scene, several minutes drive from here. Tire was replaced etc, blah blah... While there I decided to check out the metals only part of the dump. Good plan it turns out. Scored some sched 40 steel tubing in the form of a handrail, a perfectly good ( I tested it) 4 foot contractor's level, a few other items and best of all, an almost brand new 20 gallon water pressure tank.

    The pressure tank looks like new so I was a bit mystified as to why it was discarded. Upon arriving home I discovered that it is the pre-pressurized air bag style tank and the bag had failed. Excellent! I pulled off the sump cover on the bottom and removed the bag. No rust or any other sign of problems inside so the project was a go.

    I pulled out the old compressor and stripped it of all usable parts, pump, motor, plumbing and motor mount etc. Today I put it all together using the new tank.

    It isn't the most powerful compressor but it is reasonably quiet and it will run forever without complaint. It is fitted with all the necessary features, unloader, pressure relief valve, and filter-regulator as well as unregulated air fittings. The tank is rated for 100 psi service so that is where I am setting it. As it is an air pressurized hybrid tank it is designed for air service. I removed the bulkhead fitting from the old tank and cleaned it up, then welded it to the top of the new tank.

    The old compressor was built as a movable unit with wheels but this is no longer needed as I have a smaller portable that I am (was) currently using. I built it as a vertical stationary unit instead. The tripod feet are fitted with a hoop to make tipping less likely. The frame rails are bolted to existing tabs on the top of the tank. I still need to make a belt guard for it.

    A good feature is the sump. It's reinforced plastic and can't rust.

    In all, a nice project for today.

    Yes, I know the belt isn't tight...
    Last edited by Evan; 07-03-2007, 12:48 PM.
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  • #2
    NICE job.


    • #3
      What a classic example of what this site is all about, very resourceful Evan, and a High quality pleasing to the eye compresser, questions; thats a pretty large drive pulley on the motor, is it going to be Ok with the higher pressure? compliments; I dont see a whole lot of room for improvement,(air cleaner?) your design is a straight foreward no/gimmick aproach --- even if you put cooling fins on the copper pressure tube its pretty much out of the fan air and wouldnt make that much of a difference, Looks better than allot of store bought units --- all from scrap, examples dont get much better than this....
      Last edited by A.K. Boomer; 07-03-2007, 09:43 AM.


      • #4
        Evan, nice job! It certainly looks better than many I have seen at retail. Now you need to work on getting your shop more clutter. I can see too much open floor space!
        Life Is Grand


        • #5
          Looks great Evan! The only thing I would add is a belt guard if it's going to be out in the middle of the floor somewhere (as opposed to up against a wall).
          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


          • #6
            Yep, a belt guard is in the works.
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            • #7
              Got any place that can hydro test that for you? I would be nervous about a tank that held water (intentionally) lest its full of pinholes on the inside. Shrapnel propelled by even 100 psi air could do some real damage. Edit-- OK-- I just re-read your post which indicated that the removable sump allowed you the ability to inspect visually.

              I am really impressed with the professional job you did, however. Its nicely plumbed in a snug space....which isn't easy.

              Boomer asked about a that what's under the "plate" on top of the compressor head?

              100 PSI air is plenty for most things. I intentionally bought a single stage (130 PSI) compressor when I bought my big shop air compressor. I think they ought to last longer making lower pressure and the big consumers most of the time are air tools...most of which max out at 90 PSI anyway. I bought one with an 80 gallon tank, a real 5HP motor, and a big compressor head with a long stroke, rated for 100 percent duty cycle, run at low speed. To me, longevity in a compressor comes from keeping the tank free of condensation (truck bleeder valve with a rip cord) and having a big compressor run at low speed and reducing the amount of time it needs to run (big tank). It still gets good and warm, but not overly so...even when I have been able to keep it running (only during break in with the valve wide open).

              I heartily endorse the truck bleeder valve thing, by the way. Having a cable I can pull for a few seconds every time I walk by the tank, right there at eye level means it gets drained much more often than if I have to bend over to open a valve.
              Last edited by pcarpenter; 07-03-2007, 12:00 PM.
              Paul Carpenter
              Mapleton, IL


              • #8
                Got any place that can hydro test that for you? I would be nervous about a tank that held water (intentionally) lest its full of pinholes on the inside.
                The inside of the tank doesn't hold water in normal service as a water tank. The tank contains a big plastic bladder where the water is contained and the tank shell holds only compressed air. There isn't any sign of corrosion inside and it's easy to have a good look with the sump off as the opening is about 4" diameter. The inside of the tank looks like the day it was made.

                Condensation isn't a problem here. This is a semi arid climate. I have never seen the humidity go above 50% (inside) and in the winter 25% is common. I still make sure that I check the tank drain at least once per year.

                The head has a spot for a little foam filter on the intake. I might just put something better on it.
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                • #9
                  I finished the belt guard today. I also added an intake filter/muffler which makes a big difference to the noise. Now it is even quieter and you can converse comfortably beside it. I put in an auto oiler on the unregulated line too.

                  This was a fun project and it is 100% recycled/reused parts. New paint though.

                  Free software for calculating bolt circles and similar: Click Here


                  • #10
                    Evan you just too good look`s super like the guard wish I had one on mine.
                    Every Mans Work Is A Portrait of Him Self