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A multipurpose compressor possible ?

  1. Feb 24, 2009 #1
    i m curious . Can an AIR compressor be used to pump water? for arguments sake just a simple for reciprocating compressor. i mean how different can it be? one fluid is replaced with another right !
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  3. Feb 24, 2009 #2


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    What type of air compressor?
  4. Feb 24, 2009 #3
    Centrifugal type = probably.
    Positive displacement type = doubt it.
  5. Feb 24, 2009 #4


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    The primary issue is valving. A reciprocating water pump will require much larger inlet and discharge valves. Generally, air compressors are made with small valves that would have a huge pressure drop across them if water was introduced.

    A secondary issue is piston seals. Leakage past piston seals is generally a given. For water, the leakage must be safely carried away from the crankcase.
  6. Feb 24, 2009 #5


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    It is poor engineering to make assumptions such as this (although good engineering to pose the question and search out the answer). Just because you can use a single term (fluid) to describe two items, does not mean that they share similarities anywhere you wish to apply them. You yourself said "air compressor" and "pump water" so it appears that you know there is a fundamental difference between the two fluids.

    A better question would be "what are the fundamental differences between displacing AIR vs water in a reciprocating piston design."

    Q_Goest gave a great simple answer with the small differences required, but I think it's important in this case to understand why those differences are neccessary.

    As for your original question of course it would be possible, but the important questions are whether or not it could be made practical (the piston water leakage control would be dead weight to sling around when compressing air) or whether you could use ALL of the same equipment for both purposes (ie same valvetrain, driver, etc).
  7. Feb 24, 2009 #6
    Differences in density, compressibility, and viscosity (and operating speed) would cause water to just about wreck most centrifugal machines designed for air. In terms of a reciprocating compressor, the differences in valve areas required and suitable valve actions for air versus water are substantial, not to mention seals, operating speeds, compressibility, etc.

    In short, please don't try it. It is not a good idea.
  8. Feb 25, 2009 #7
    thanks a lot evry1 roadrage :) ! i knew it wouldn't be a very practical one but u are saying it can be done.
    lets say i use some other gas instead of air(forgetting all corrosion effects on the material of compressor) say ammonia. Now if my reciprocating compressor gives air at 7 kg a flow of 60 CFM with a motor 20 hp. what if i use the same for ammonia. can i roughly predict the parameters at the delivery. what are the Fundamental properties of gas that decide the discharge parameters.
    Last edited: Feb 25, 2009
  9. Feb 25, 2009 #8
    Pumping liquids in a recoating compressor designed for air and not liquids usually results in damage due to what’s called a hydraulic lock. It you are lucky it will just stall but with enough force you can bend rods. Examples where this has happened are auto and aircraft engines as well as the early fridges, which used piston compressors.

    If it is designed to pump liquids that is a different matter.
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