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Prsssure vs. air flow baseline

  1. Jul 6, 2006 #1
    I am working on an air flow vs pressure chart for a variety of valve components for work and I am hoping someone may know where I could get some comparative baseline data.

    My setup is a 4' long, 2" diameter PVC pipe with one end connected to a large air compressor tank with a ball valve for regulating the flow. Near the other end, I have an air flow transducer (Omega FMA-906) and a pressure transducer (Omega PX303). The end of the pipe is reduced by a series of graduated fittings that terminate at different ends that are designed to fit the valves I am testing.

    I am able to check my pressure readings with an analog pressure gauge, but I don't have the same ability with the flow without significant setup changes. I am hoping there is some type of baseline data available for typical flows in a pipe with a constricted end. If anyone could point me to a resource for that data, that would be great!!
     
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  3. Jul 6, 2006 #2

    FredGarvin

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    What is the signal output from the flow meter? You should get a calibration curve from Omega. That's your check. Is there a reason why you don't trust the cal cert?
     
  4. Jul 6, 2006 #3

    Q_Goest

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    It sounds like you're trying to set up a flow test bench to determine the Cv of your valves, is that right? From reading this it sounds like you have an air tank, a ball valve on the tank outlet to regulate pressure or flow, a 2" pipe leading to a point that a valve is being tested, and I assume the outlet of the valve is venting to atmosphere.

    There are some standards which cover flow rate testing for valves if that's what you're looking for. They basically tell you to measure upstream and downstream pressure on your valve and apply the equation to determine Cv. If your valves are various sizes such that your flow meter can't handle the full range, you should probably purchase a few different flow meters to handle the range. Electronic air flow meters of any kind are not cheap, so if you're concerned about cost, I'd suggest a rotometer.
     
  5. Jul 6, 2006 #4
    turst in calibration

    I do trust the calibration of the instrument -- It has more to do with the setup. Any setup will have different amounts of chaos and thus could affect the instrument reading depending on where it is located in the tube. I can certainly use the data I have, but I thought a "second" opinion would be nice.

    Yes, this is venting to the atmosphere. And yes, my flow meter is sufficient to cover the flow amounts I need to test.
     
    Last edited: Jul 6, 2006
  6. Jul 6, 2006 #5

    Q_Goest

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    If you're just looking to back up the meter you have, a rotameter might suffice. It will get you to within a few percent for less than $100. Check out McMaster Carr or try ThomasNet.
     
  7. Jul 6, 2006 #6

    FredGarvin

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    Granted your uncertainty will change slightly depending on the valve that is in line. However the "chaos" as you state it, inherent in the system will be eclipsed by the error in the measurements.

    Depending on the expected range of velocities, you could also employ an orifice measuring station as a check.
     
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