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Thread: Ganging two small air compressors together

  1. #1
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    Ganging two small air compressors together

    I have 2 of these: (one is actually an older model with a smaller 3/4 hp motor)
    Emglo 4gal.jpg
    And 1 of these:
    Hundai portable.jpg

    If I were to feed both compressors into the portable tank and then draw off of that, would that be a little like having a larger compressor, specifically for spraying?

    Or would I just have a bit more capacity without any greater ability to 'keep up' with the draw?

    It's just a thought that popped into my head today. I'm trying to make do with what I have.

  2. #2
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    I don't know about smaller compressors, but when my Dad replaced his compressor that broke he salvaged the tank (30 gal.?) and added a 60 gal. 3 hp compressor to his existing tank inlet because the outlet was already plumed to his shop. There aren't any problems, but when refilling it takes longer because of the extra tank, which is more work for the compressor and motor. He does some auto-body work (painting, pneumatic sanding, and sandblasting), so thee extra reserve comes in handy. Running the auxiliary tank will be fine unless the compressor's setting exceeds the other tank's rating. Running two compressors might not work. Even though they are identical, one might start pumping before the other increasing the tank psi in the other tank one causing it not to kick in resulting in just an extra storage tank. As far as spraying goes, my 2 hp 25 gal. compressor keeps up just fine. If you want to use a compressor for spraying get one from HF, or a turbine unit made fro spraying (from HF).
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  3. #3
    Two identical compressors would keep up twice as well as one. They would refill your system twice as fast. The extra tank would lengthen your usable time between refills, but increase downtime if the compressors still can't keep up.

  4. #4
    Regarding running two compressors: I have a 5HP and a 3HP, both single stage. The 5HP can't keep up with my sandblaster so I got the 3 HP used and rebuilt it. I read all about ways to plumb them together - check valves and all that. I couldn't seem to get a definite answer on how to do it. So one day I just plugged the two if them into the sandblaster and went at it. They worked fine. The one would cycle on and off to supplement the other and I actually had the capacity to keep up with the sandblaster, plus a bit extra. Neither one was set to a pressure above the rating of the other, of course. I only couple them together when I run the sandblaster.

    With both your compressors hooked up to that air tank, you would have the CFM of both compressors plus some additional air capacity with the extra storage tank. You'll be able to go longer before the compressors kick on but then they'll run a little longer to fill the extra tank.

    Bill
    Last edited by Bill Geibe; 03-21-2013 at 9:42 PM.

  5. #5
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    I guess the thing to do is hook 'em up and see how it goes.

  6. #6
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    Yes, They will work. They won't be as efficient as a single unit, but they will work.
    This configuration is used in industry all over the world, every day of the week, 24/7. At times we have hooked up over 12 large, portable diesel powered compressors simultaneously. 4" hoses from each compressor, to a large air receiver tank, the size of your car, and a common discharge header.
    The standard configuration I deal with is three in service, One in lead and two in standby. These are further backed up by two more units.
    You'll be missing some control and logic schemes, but the basics will work. In order to really benefit you will have to size all of your orifice restrictions for flow. Upsize the hose/pipe/tubing between the tank and the compressors. The final unloader valves, or diaphragms, will work as crude check valves. If your regulators are downstream sensing the system will equalize itself.
    Vacuum pumps work the same way. I have two 70 scfm, at 28"hg, units hooked up in parallel when they are used.
    As I said, it's kinda crude, but it will work.
    Last edited by Mike Cutler; 03-21-2013 at 11:45 PM.
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  7. #7
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    Yep - you'll be fine.
    As Mike pointed out, compressors are ganged all the time.

    Just make sure you run each compressor off a seperate electrical circuit.
    My Coleman draws a full 15 amps and my Ingersoll Rand "hot dog" (similar to your Emglo) draws 14.5amps.
    My sub panel in the garage is only 30 amps. I have to run one off the sub panel and the other off the house panel, otherwise I run into starving one or the other for current.

    Oh yeah, make sure the aux tank is rated for the same pressure as the compressors.
    (IIRC, Emglo compressors (DeWalt) operate around 200 psi.)
    Every loaf of bread is a tragic tale of grains that could've become beer.......but didn't....

  8. #8
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    Your proposed setup will work just fine. I actually read an article about this very thing (minus the extra tank) quite a few years ago in either Journal of Light Construction or Fine Homebuilding. I remember from the article that the contractor cobbled together an air fitting that he and his crew affectionately named, "The Double Dongle"--basically a T with two male quick-connect fittings and a female quick-connect, IIRC.

    Keep in mind, however, that you will still have the duty rating of the two compressors to monitor. I have a 12 year old P-C double stack, and it has excellent flow for its size, but its duty rating is 50%. So, 30 minutes of every hour it can run. I've used that to my advantage. If I can spray a coat of finish on something (like a trim package) in 30 minutes, with the compressor barely keeping up, then I can let it sit and cool for 30 minutes (or more) and not exceed the duty rating. I also have an extra tank, which was very useful when my father and I were roofing my house, running two roofing nailers. When we were both going gangbusters, the compressor would occasionally get a little behind, leaving nails proud. With the tank hooked up, we were good to go because it would help get us through periods when we were both nailing, then recover while we grabbed more shingles or moved or whatever because it meant more air available at the regulated pressure.
    Jason

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  9. #9
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    Thanks all- this is great to hear. I can't believe I never thought of this before, I've had this equipment for many many years and always wished I had a bigger more robust compressor.

    As I said, I'm trying to make do lately with what I have. I've even got all the hoses and fittings I'll need. Sweet!

  10. #10
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    I have seen tradesmen in Taiwan ganging compressors all the time, possibly because they won't find a 220 line to feed a large one and it's easier to carry a bunch of small ones than a single large one.

  11. #11
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    Quote Originally Posted by Jason Roehl View Post
    Keep in mind, however, that you will still have the duty rating of the two compressors to monitor. I have a 12 year old P-C double stack, and it has excellent flow for its size, but its duty rating is 50%. So, 30 minutes of every hour it can run. I've used that to my advantage. If I can spray a coat of finish on something (like a trim package) in 30 minutes, with the compressor barely keeping up, then I can let it sit and cool for 30 minutes (or more) and not exceed the duty rating. I also have an extra tank, which was very useful when my father and I were roofing my house, running two roofing nailers. When we were both going gangbusters, the compressor would occasionally get a little behind, leaving nails proud. With the tank hooked up, we were good to go because it would help get us through periods when we were both nailing, then recover while we grabbed more shingles or moved or whatever because it meant more air available at the regulated pressure.
    +1

    As others have said, the two compressors and tank you show there will perform as you wish for spraying. Now, let me share with you the probably small thing you won't be getting with this KISS solution.

    Each compressor turns on when its low pressure switch setting is reached. Even with two of the same model, one setting likely slightly higher than the other. This will make that compressor perform in "lead", with the other in "lag". When connected this way, you can expect to wear the "lead" compressor faster than the "lag".
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  12. #12
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    The proper way to run 2 compressors is with a 1-2 switch.
    Comp. 1 runs a cycle, then 2 runs a cycle. Back and forth.
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  13. #13
    "Lead/Lag" is a good way to run a system like this. The compressers will have different pressure settings. The trick is to alternate them, say weekly, to even the wear and ensure that both are working properly.. You may be able to wire a suitable switch. Then it's a case of remembering to switch over.

    I used to run a plant with a number of cooling circuits, all with two pumps in a lead/lag configuration. Then there was a Sunday night at 10pm routine (Start of the first shift of the week) where the control system, among other things, switched over all the pumps and screamed if the new lead would not cut in. In the case of a workshop one could mentally associate the changeover with some other regular task like sweeping up.

    Essentially the same system was used for the supply of services. Air Compressors, Ammonia Conpressors, Water Filters were all on a lead/lag system.

  14. #14
    It is fairly common in industry to have accumulator takes near the point of use for compressed air, particularly when there are long runs between the compressor and point of use. It will take longer for the tanks to fill up on start up, but the accumulator will handle any short term surges in demand without significantly dropping the pressure in the system. The larger the tank, the greater the surge in demand it can handle.
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  15. #15
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    Welp, so much for that idea!

    I turned on my older 3/4 HP compressor today and halfway through the first cycle, one of the tanks blew a small hole in the bottom.

    My first compressor has died. Always sad when a tool dies before it's original owner.

    So is it repairable? Weld the hole closed? Is it worth it or is it safe to assume the entire bottom is compromised inside?

    I'm not exactly the best at draining the tanks regularly.

    But Ill be better now with my newer one...

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