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  • Making an air compressor

    After reading Forrest Addy's thread on air compressors and the responses it got me thinking about making a compressor from an old engine. Do any of you guys know where I could find more information on this?

    I live in the suburbs, and my shop is a 2 car garage, so I would need to power it with an electric motor as I can't put it outside, and I obviously don't want to run it off gas inside the shop. How many HP do you think I would need to run something like a small 4 cylinder engine? What about an engine off a bike?

    I'm looking to build this thing fairly cheap, and would mainly be using it to run a spray gun, however, more air tools will come in the future. My goal is to have something that can put out 15 cfm (or more) @ 90psi, and use a fairly small reserve tank as space is limited. Do you think this is a reasonable project? Any help is greatly appreciated.
    Andrew

  • #2
    If you're going to have to look for a scrapped engine as the basis of your project, you'd be better to 1. keep an eye on the classified ads in your local paper. 2. shop the pawn shops. 3. while scouting for an engine, also look for a junked air compresor off a semi truck engine or a junked Freon compressor.

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    • #3
      I once made a compressor from a 5 HP tecumseh engine. I did not need it I just did to see if I could. I can say that it worked, made a lot of air, but it also pumped some oil, so no good for spraying. I dicarded the original head and made another that would accept two reed valves. If I were to do it again I would also discard the rings and make new ones from Delrin or some other plastic material. Might even bore and hone the cylinder in an attempt to reduce oil consumption. I think that was my problem I used an older engine. A three to five horse motor would be sufficient. Wait a minute??????? OK I am back I just went out and checked, I still have the head I made with the valves I can put them in a box and you could have them for the cost of shipping.

      Northern Tools sells compressor pumps for which you would need to supply a motor and tank. A single stage 13.2 cfm @ 90 psi=$299.00 and a two stage 15.9 cfm @90 psi = $369.00. IMHO a lot of bucks, may as well buy a complete unit.

      An idea that I have had for a long time is to make a compressor from a running VW engine. Two cylinders will run the unit and two will pump air. It can be done. I have seen plans in some mag. years ago to make one from a V8. Four running and four pumping. I thought of using the VW because #1, it is smaller and #2, it is air cooled.


      ------------------
      Paul G.
      Paul G.

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      • #4
        I've thought about doing that, using an old snowmobile engine, driving it with an electric motor. The four cylinders would give a reasonably smooth pressure delivery, maybe enough so to eliminate the tank altogether, of course, that means running the motor constantly, and some kind of valve would be needed to bypass all unused pressure. Much like a power steering pump is set up. My reasoning had to do with the large flow capacity possible with a four cylinder, coupled with the small capacity of a reasonably sized tank. The motor would be cycling on and off way too much, may as well run continuously, no tank required. Just a suitable valve. Of course, you could run the 'engine' slowly enough to be adequate for the most hungry air tool, but no more so. That might reduce the horsepower requirement for the electric motor driving it. Another benefit would be that the temperature rise of the compressed air would be lessened having four cylinders doing the pumping, so the heat loss, ergo energy loss would be less. These are just some of my theories on this , so take it as that. I've not yet built my own compressor, though I plan to, and am looking at a tankless setup. One other thing to consider is the 'engine' will essentially be sucking a high vacuum, which is the worst case scenario for oil passing the rings. It would have to be in good shape. All comments and criticisms welcome on these ideas.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Well, as a project for fun, why not?

          As a practical way of getting a compressor, maybe not.

          There are a fair amount of compressor pumps with no tank around, due to tanks rusting, etc.
          Used to be refrigerator pumps, back in the bad old days. I have a friend whose farm has a fridge pump compressor, works great.

          Those things were designed to pump air well.

          Since engines are usually available because there is a cylinder or major bearing problem, that is one issue. Also the oil throwing issue.

          And lifetime as well. Oil distribution may not be very good on a splash-lube engine at lower speed. And some of those engines are low hour life engines , usually available because they are about wore out.

          Finally, most are low compression, meaning they will not push as much air as a real pump with equal swept volume. You would have to fill up the chamber somehow to get better efficiency.
          If you make a new head, might as well make the whole thing.

          Still, its an OK fun project. And better than no compressor if that is the only option out in the sticks, or a remote location.

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          • #6
            If you use a four cylinder engine you could make it a four stage compressor. have one cylinder feed the next so each clinder only needs to compress the air a little bit. but since most engines create 120 to 180 psi in one shot I don't think overworking it will be and issue
            kerry

            [This message has been edited by Kerry.S (edited 05-06-2003).]
            Rule #1 be 10% smarter then what you\'re working on.
            Rule #2 see Rule #1

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            • #7
              Back in the days when AMC still existed as a seperate enitity they did a quite substatial business in supplying motors for various aplications. International was using the inline sixes and v-8s until they installed their own v-8 machining equipment and still continued to use the six. One other custumer at one time was a natural gas pipeline company in Canada that bought AMC v-8s with a special cam shaft and intake manifold. Four of the engines cylinders operated as internal combustion while the other four were used to maintain the pressure in the pipeline. And the four that were running in the combustion mode ran off of the gas supply in the pipeline
              Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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              • #8
                Air compressors are too cheap to make it worthwhile to build one from junk parts. Rebuilding a good cast iron compressor makes sense if you get a good one. Ingersoll-Rand is expensive and hard to rebuild. Quincy, Kellogg, Curtis, Saylor-Beal are all good solid compressors and pretty easy to rebuild. Get as big tank as you can. The bigger the tank the less often the compressor will cycle and it is the starting and stopping that wears them out. The compressor should not start more than once every ten minutes or it will most likely smoke the motor or the compressor. Constant running is not hard on the compressor. Get a big piece of pipe say 4-5 inches in diameter to use as the first receiver and put a ball valve on the bottom with the pipe standing vertically. This big piece of pipe will condense and catch a large part of the water and oil vapor coming out of the compressor. Put another ball valve on the air tank so you can drain the water there also. After that you can put on a refrigerated air drier to give you real dry air and then put on a coalesing air filter. The air you get from this set up will do a great job for painting and for most instrument air applications. The air is still unsafe to breath though. You don't need the refrigerated air drier for most painting but it extends the life of the the air filter a lot so you save some money on filters and are less likely to screw up a paint job.

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                • #9
                  If I was going to waste the time to build a compressor from scratch, it would have to be a rotary screw compressor. No point screwing around - I always say - or was it "poo or go blind"? For what a good Cast iron compressor cost, why bother? Or better yet, find an old one no one wants and rebuild it! (Yeah!)

                  I knew a guy that was given a tree stage for free - worn out. It cost him $500 for the sunnen CK10 hone job, parts, and a 10HP single phase motor. It could run 3 snap-off impact wrenches and a 1-1/2" impact wrench all day and stay at 200psi. A commercial unit to do the same would have cost $5000. So it was worth the effort.

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                  • #10
                    Just one more sugestion: If you plan on running air tools, go with a compressor that makes at least 15cfm @ 120psi. More (cfm) is better. Also, 90psi at the regulator will be down to 80 or less by the time it gets to the end of a 50' hose. Some of the new sanders and die grinders use only about 4cfm @ 90 but most others need 9cfm and above. I've got a few that take 15 and a spray gun that takes 17! Make sure you check that when buying air tools.

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                    • #11
                      I got my air compressor from a seniors assisted care living center. They have to replace the fire sprinkler compressor after so many hours of running, so I got a nice 5 HP compressor from them. Then I called around to the places that repair auto shop equipment, they a 100 gallon tank that they took the compressor off of and gave me the tank for $50. This was a poor mans way of doing it.

                      From HF, I bought a 4.5 HP compressor with a 21 gallon tank. I use the 100 gallon tank to build volume, works much better and doesn't run all of the time. Things are so cheap, that building one is for the experience, not the need.

                      Jerry

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                      • #12
                        I once worked on a steam driven air compressor but not the usual type,it looked and operated like a walking beam steam engine,had a big cylinder on each end one for steam and one for air,I don't see why you couldn't make one with an electric motor driving an eccentric just a thought,I have a Linsay 80 cfm that is a 360 Dodge v-8 that runs on four and pumps on the other, they did away with the factory head and made their own with popet valves instead of the automotive type,as long as the rings are new and not subjected to combustion temps. they seal good and don't introduce any more oil than a regular compressor would.I like Thrud's idea if you are going to do it build a screw,or better yet find a commercial unit that the engine is blown up in and modi. it.Maybe even build a vane type compressor they are pretty simple.
                        I just need one more tool,just one!

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                        • #13
                          I have a book I bought about fifteen years ago called "Build Your Own Sandblaster". The compressor for this rig is a 390 Ford engine set up simular to what weirdscience posted above. The book was written by Donald E. Ribbing and Robert D. Kirk, published by Design Publications, PO Box 102, Columbia, Ill.,62236 and is item no. 3697. Not sure if it's still in publication, nor did I ever attempt to build one, so I can't address the accuracy of the plans.

                          [This message has been edited by x39 (edited 05-06-2003).]

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                          • #14
                            OK, if you are gonna use a 4 or maybe even an 8 cylinder engine, a litle efficiency won't matter. And if you want volume, that will indeed help a ton on that too.

                            I don't wanna move that sucker, though.....

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                            • #15
                              We kind of discussed this a while back (I said we "walter mitty engineered" the gas engine idea. I did not know they were so common. We thought using three cylinders to feed the fouth (in a V8) would give much high SCFM than running al four in parallel (which is what I gather is being discussed). The three feeding four would allow for a heat interchanger between stages.

                              And on any home made rig- don't forget the unloader valve if the compressor will have to start against tank pressure.

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