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Air line gauge in a T fitting, error vs flow

  1. Oct 20, 2011 #1
    Professor forgive me it has been many years since my last physics problem, but I was looking at the pressure gauge mounted in a T fitting on our shop compressed air line, and how the reading dropped when various high cfm tools were in use. As I understand it the indicated pressure reflects two things, flow losses in the piping system, and measurement error due to mounting the gauge in a T fitting 90 degrees relative to the flow.

    I am curious about the size of the error from the Bernoulli effect in the T fitting.

    Shop air is regulated down to 125 psi at the main tank.
    Piping is 1/2" schedule 40 actual ID 0.622 inch.
    T fitting is 1/2" female NPT on each connection, actual ID about 0.840 inch, length 2.1 inches, but with up to about 0.750 inch of the pipe threaded into each end.
    Gauge mounted in top of T with a short 1/8 npt adapter.
    A large impact wrench uses 10 scfm, and a sand blaster uses 15 scfm.
    A fair estimate of pressure drop in the piping is 3, 5, and 12 psi relative to 10, 15, and 25 scfm flow.

    What is a reasonable diameter to use for the T given the proximity of the input and output pipes?

    What would the error on the gauge be at 10, 15, and 25 scfm air flow?

    Thanks
     
  2. jcsd
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