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Thread: How to use two air compressors to increase CFM

  1. #1
    DIY Junior Member cicerored's Avatar
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    Default How to use two air compressors to increase CFM

    Hi,

    I have read that it is possible and safe to combine the output of two air compressors for high CFU applications. I was wondering how to accomplish this. It seems to me that using an unregulated air tank would be the best way. So the input of both compressors would be connected to the air tank and a 3/8" hose for the output.

    Anyone ever done this or have advise?

    Thanks
    Red

  2. #2
    Homeowner Thatguy's Avatar
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    You likely need check valves on the compressor outputs to prevent the air from one compressor going backward into the other. Putting them in parallel increases CFM, in series increases PSI.

    Using
    http://en.wikipedia.org/wiki/Affinity_laws
    or
    http://www.google.com/cse?cx=partner...nity&sa=Search
    you might be able to predict the output PSI and CFM.

    You'll need the "pump curve" for each compressor, the PSI vs. CFM curve.
    Last edited by Thatguy; 11-11-2010 at 03:26 PM.

  3. #3
    DIY Junior Member cicerored's Avatar
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    The check valves are a great ideal. This set up would be parallel, right, with the two tanks into one?

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    Moderator & Master Plumber hj's Avatar
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    quote; in series increases PSI.

    The ONLY way to increase PSI is to adjust the pressure switch. Put check valves on the outlet of the two compressors and use short hoses to connect them into a tee. It will also work without the check valves, because both have to be set to the same pressure.

  5. #5
    DIY Junior Member cicerored's Avatar
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    I just want to increase the CFU/Minute

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    Homeowner Thatguy's Avatar
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    Identical compressors, right?

    I don't see a difference between having two compressors running into one tank and your output is taken from that single tank
    or two compressors with both their tank outputs running into a tee.

    Just make sure there is no way to overpressure any tank.

    Can you post the specs of the compressors? It may make a difference with positive displacement compressors vs. others.
    Last edited by Thatguy; 11-11-2010 at 06:55 PM.

  7. #7
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by Thatguy View Post
    Identical compressors, right?
    Either way is fine since each motor must have its own pressure switch anyway ... and both motors even could be pushing air into just one tank with their respective pressure switches sitting side-by-side on a tee (or possibly even connected to just one switch if the switch can handle the load). Also, no check valves are needed (or even a good idea) anywhere other than between each motor and its tank. Using check valves in the outputs of two tanks teed together accomplishes nothing more than making it impossible for either motor to send air into the other tank.

    Edit for correction: A bleed valve and check valve likely *will* be needed for at least one tank in order to manually bleed that tank down to get that motor started at all ... and that means my thought of two pressure switches on a tee on one tank also needs some further thought!
    Last edited by leejosepho; 11-12-2010 at 06:04 AM.

  8. #8
    Plumber jimbo's Avatar
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    Multi stage compressors are used for higher PSI. But as built, the guages and limit switches of "regular" compressors would not allow you to get higher PSI. I also doubt that the compressor itself would handle the much higher output, even though the DP is the same. Theory is correct,though. We used 4 stage compressors on the boats for the 4500 PSI air system.

  9. #9
    Homeowner Thatguy's Avatar
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    If both compressors are always under load you may not need a check valve. Things may get weird when the load is removed.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Most compressors have an "unloader" on their switches so that the motor can start under load. The check valves would be so that the compressors could be disconnected without having turn off both compressors and drain the pressure from them.
    Last edited by hj; 11-13-2010 at 07:59 AM.

  11. #11
    DIY Senior Member dlarrivee's Avatar
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    Quote Originally Posted by jimbo View Post
    Multi stage compressors are used for higher PSI. But as built, the guages and limit switches of "regular" compressors would not allow you to get higher PSI. I also doubt that the compressor itself would handle the much higher output, even though the DP is the same. Theory is correct,though. We used 4 stage compressors on the boats for the 4500 PSI air system.
    He isn't looking for pressure, he is looking for volume.

    CFM is NOT PSI.

    HJ is correct, almost ALL newer compressors have an unloading valve so that the motor/compressor doesn't have to fight the compression of the full tank.

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    DIY Junior Member raj's Avatar
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    Default New compressor requirement

    Here is my brand new requirement…..

    “I’m looking for a compressor mechanism which should give me around 3500psi of air pressure.
    By using the natural air, at room temperature, is it possible to create the pressure of around 3500psi by using an air compressor. The compressors which are already available in the market are costing around $3000. It is too expensive for my usage and i cannot afford that much money.

    So that, I’m planning to build a new compression mechanism which suits my requirement.

    Can anybody help me how to generate this pressure or are there any other air compressors which are available in the current market for less than $2000.

  13. #13
    DIYer, not in the trades LLigetfa's Avatar
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    In what way is this related to the 2 year old thread you dug up? I don't see anything within it that would apply.

  14. #14
    Moderator & Master Plumber hj's Avatar
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    You are trying to fill scuba air tanks, and NO standard compressor will come anywhere near that pressure. Most are limited to 150 pis MAX. Using them, the only thing you can increase is the volume. The pressure you want requiress specialized components and they would be highly regulated to make sure they are kept in a safe condition at all times. Otherwise, you would be working with a "bomb".
    Licensed residential and commercial plumber

  15. #15
    DIY Junior Member raj's Avatar
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    You are right HJ...i'm trying to fill Scuba air tanks...is there any way to make this new compression mechanism by my own....
    i heard that, bauer compressor, junior II gives the pressure of 3500PSI. but, this is too expensive. if possible, I'm planning to come up with a new solution for a less price. I just want to know the possibility, whether is it possible to manufacture or not and how difficult it is to manufacture a new compressor.

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