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  • Building a compressor

    Rebuilding what is already a homemade compressor to be precise. Here's my current compressor built around an old single phase compressor and a 100l 26 bar tank, and there's also the new compressor block I acquired. It's supposed to be able to give around 275-355 liters / min @ 6 bar, depending on how fast you run it, the specs I've found says this block could be run at 920 rpm or 1275 rpm. Or I guess since I am making or buying my own smaller pulley, any speed in between the two. 355l is around 12 cu.ft. and 6 bar is a little less than 90 psi.



    The plan is to mount it on a beefy console around where the current compressor is, along with a suitable motor. Or alternatively I mount the thing on the other side of the wall (outside) and put the compressor in an enclosure mounted on the wall up from the ground. Leaning more towards putting on the outside now.

    I have this 4kw 2800 rpm motor that i am considering, thinking of aiming for a speed of 1000rpm on the compressor: I think that will satisfy my needs.


    But I am not 100% on that, I also have this 3kw motor (on the right) which might also work, it already has feet so less work to make it suitable:



    To be continued.

  • #2
    Wow you have some nice parts. *cough* I would want to err on the side of the larger motor and run the pump at a slower RPM for longevity. It looks like it weighs a ton.
    25 miles north of Buffalo NY, USA

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    • #3
      If you check your specs closely you will find the two different PUMP speeds also have a HP requirement to drive it at that speed and pressure. The faster you run the pump the more power it requires. The higher the cutoff pressure the more power it requires. So you can't just randomly choose a speed and motor power. In the end you monitor the motor current and adjust the other two , speed or cutoff, to prevent overcurrenting the motor.

      lg
      no neat sig line
      near Salem OR

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      • #4
        Originally posted by larry_g View Post
        If you check your specs closely you will find the two different PUMP speeds also have a HP requirement to drive it at that speed and pressure. The faster you run the pump the more power it requires. The higher the cutoff pressure the more power it requires. So you can't just randomly choose a speed and motor power. In the end you monitor the motor current and adjust the other two , speed or cutoff, to prevent overcurrenting the motor.

        lg
        no neat sig line
        This.
        I just need one more tool,just one!

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        • #5
          The HP requirement is 2.2 vs 3 kw so that is known and my motors are inside spec.

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          • #6
            I have a similar (in theory) compressor built in setup. I have a stand with a 5hp motor, emglo v4 pump, aftercooler with drain and a new 60g tank. Mine runs around 700rpm and is very quiet. I get around 20cfm

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            Attached Files
            Last edited by legendboy; 05-01-2021, 12:03 AM.
            https://www.flickr.com/photos/csprecision

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            • #7
              20cfm sounds quite extraordinary for that size compressor to me

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              • #8
                Dennis you are really being mean to all those folks across the big ocean. Flaunting your 3phase plugs everywhere. I love it!
                Location: The Black Forest in Germany

                How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                • #9
                  This is my version of building a compressor. New 60gal tank, compressor pump from ebay, 5hp single phase motor, start contactor, pulleyed to 650rpm, belt guard aftercooler, water trap before the tank.
                  It runs rather quiet with clean air. End result is a good solid 4hp compressor per amp load & CFM.

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                  • #10
                    If you can tolerate the reduced output, do the slower speed. I have always been a fan of big, slow compressors because they seem to be a lot more reliable due to reduced wear and tear in the nominal running condition.
                    -paul

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                    • #11
                      no reason for reduced output running slower, that is why you get a bigger pump from the outset, this pump would be 7 1/2 or 10HP from one of the big manufacturers, but I have big cubic displacement and running it at 4hp motor amps.
                      And it is single stage, when it is really called upon to deliver air, it is there at the pressure I need it, in the 80-100psi range.

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                      • #12
                        In this case the pump or compressor block as I think of it is a fixed entity though. The lowest this block is rated for is 975 rpm so I am aiming for that, I think providing 275 l/min @ 90 psi should be good enough for my purposes. If not I can always gear it up.

                        Are your compressors oil free or oiled I wonder. This is an oil free compressor block, came from the local hospital in the city and used to provide breathable compressed air. I want to build a supplied air system for 2k spraying in the future so that's a good start, some extra 3-stage filters and a 3m system for my 6800 mask, all quite expensive though so it'll have to wait.

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