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Required water pressure to find air leak

  1. Jan 21, 2015 #1
    I have an air leak somewhere in a coil or 20 feet of pipe in a mechanical room next to a transformer. I have 160 psi of air on the system and it dropped 30 psi in two days.

    I have tried to find the lead with 60 psi of water currently but no success. I do not want to put a lot of water pressure on the system and have the leak show itself in a marvelous fashion and ruin the transformer.

    My question is: How can I calculate how much water pressure is needed to identify the air leak at 130 psi of air?

    I know the viscosity information and the surface tension for water and the viscosity for air but I have no idea on how to apply them to an equation. I have zero success finding anything online about this, so any help would be greatly appreciated.
    Thank you.
     
  2. jcsd
  3. Jan 21, 2015 #2

    Bystander

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    Coil of what? Rubberized air line? What's the volume of the line and pipe? If this is "utility" air for driving pneumatic tools, you've got the tightest system I've ever heard of --- as in not broken, don't fix it. If it's something else, instrument air, or whatever, and has to be tight, check the "hard" plumbing separately from any soft/flexible lines.
     
  4. Jan 21, 2015 #3

    Quantum Defect

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    Larger leaks in gas lines can be checked with "Snoop" (basically soapy water). Smaller leaks can be found with a He leak detector -- overpressure the system with He, and scan the outside with a probe. Some other kinds of commercial gas detectors can be used, as well, in a way similar to the He leak detector. If you are near a physics department, they may have a He leak detector for detection of leaks in vacuum equipment.
     
  5. Jan 21, 2015 #4
    It's a copper coil for warming air that is going through a Air Handler Unit. I'm currently testing it with air to verify there are no leaks. Water will be flowing through it in the future to heat the air that passes through the coil. There are zero flexible lines in this system, it is all hard copper piping.

    I just want to figure out how to determine what pressure of water I would need to identify the leak I have with 160 psi of air.
     
  6. Jan 21, 2015 #5
    I have sprayed everything I can with a micro leak detection fluid already with no success, which leads me to believe that the problem is in the coil which I cannot spray down. I agree with He use but that is not practical where I am located or I would definetely do it.
    I would just like to put enough water pressure to it in order to find the leak I have with air. There has to be some sort of mathematical formula to use that can accomplish this.
     
  7. Jan 21, 2015 #6

    Quantum Defect

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    If the system is going to be filled with water (low pressure) for a heat exchanger, I might not worry about such a small air leak at 160 psi. You won't be running anywhere near that pressure, no? It may not leak under normal operating conditions.

    If you are committed to finding any possible water leak, another strategy is to put some very fluorescent water-soluble dye (fluorescein or rhodamine) in water, fill the system, and look for a leak with a uv lamp -- they have these at pet stores for finding cat pee! Or you could fill the system with cat pee.... ;)

    The only draw back with this method is that your system will be filled with a brightly colored dye that may be difficult to clean out. If the cooling water is closed cycle, then it doesn't really matter.
     
  8. Jan 21, 2015 #7
    The system will only be around 50 psi of water which I know will not leak, but my foreman has this strict requirement to pass with no leakage at 150 psi of air in this mechanical room. I know that this is rediculous, but I am just doing as I am told.

    The dye will not work currently since it is not leaking any water which would be visible and I have to get the pressure of the water higher to counter the higher viscosity and the surface area that it has over air. I just need to know at what pressure water will start to show itself.

    With a mathematical formula in hand I can show the foreman that this is the pressure I have to take it to in order to identify the leak. He is very anal about getting water in the transformer and blowing it up. I need to show him that 60 psi of water will not equate to 160 psi of air for leak detection purposes. Any sane person can obviously tell that air will leak through an opening before water will but there is no reasoning with him. I need some cold hard calculations to show him
     
    Last edited: Jan 21, 2015
  9. Jan 21, 2015 #8
    As for the volume, I have about 20 gallons worth of piping. I could convert it to cubic feet but gallons works too.
     
  10. Jan 21, 2015 #9

    Bystander

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    So, four "gallons" of air loss times twelve atmospheres is 48 gallons of air in two days is around a "gallon" an hour. You could be blowing the "snoop" away from the leak so fast that you won't see bubbles. Cut the pressure and look again.
     
  11. Jan 21, 2015 #10

    berkeman

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    If he is doing his job, he will not accept what you have gotten via the Internet. The liability issues are too great. Thread is closed.
     
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