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Help with measure air flow rate with pressure difference in a cylinder

  1. Feb 6, 2014 #1

    I've got a horizontally moving piston in a pneumatic cylinder, the piston is moving backward to suck the air into the cylinder from a hole at one end, this will lead to an air flow rate. I would like to measure the air flow rate at that instant. I was thinking of with a pressure sensor attach to the cylinder, i can measure the pressure difference. By using Bernoulli's equation, i can calculate the air flow rate. Is this approach correct? and what pressure sensor would be suitable?

    If you need me to explain more on the details, I would be more than happy to help you.

    Thx guys.
  2. jcsd
  3. Feb 9, 2014 #2


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    Welcome to the PF.
    I think more information would help find you an answer.

    It would be good to know the cylinder diameter, stroke and rate of movement?
    Some idea of the orifice = hole size, would also be useful?

    How you measure the airflow will depend on why you need to know it?
    At what instant(s) during the retraction stroke do you need to measure the air flow?

    Given that information it should be possible to get a quick answer.

    As the air on each side of the orifice will have a different pressure, the volume flowing will depend on the pressure where you measure it. This suggests a pressure independent mass flow meter might be appropriate.

    Some light reading; http://en.wikipedia.org/wiki/Flow_measurement
  4. Feb 9, 2014 #3


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    Given the information though it should be possible to get an answer analytically rather than by testing. You would just need to know the things Baluncore asked for. The flow in this case is almost certainly compressible, though, so it is unlikely Bernoulli's equation will be of any use.
  5. Feb 9, 2014 #4


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