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Homework Help: Calculating percentage change in flow rate through a valve

  1. Jul 29, 2015 #1
    < Mentor Note -- thread moved to HH from the technical forums, so no HH Template is shown >

    The max flow rate through a control valve with an equal percentage characteristic is 10 m3/h. If the valve has a rangeability ratio of 50:1 and is subjected to a constant differential pressure, calculate the % change in flow rate through the valve for valve lifts at 10% intervals.

    It asks to show that the vavle is indeed equal % by finding the change in flowrate from one interval to the next.

    I am just slightly stuck on which equation to use for this.
    Last edited by a moderator: Jul 29, 2015
  2. jcsd
  3. Jul 29, 2015 #2


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    is this homework ?
    looks like it

  4. Jul 29, 2015 #3
    It's similar to a question I have for homework but not the same. I am just needing a bit of help with equations and which one to use as I am stuck?
  5. Jul 29, 2015 #4
  6. Jul 29, 2015 #5

    jim hardy

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    That link appears to size valves for on-off control.

    Equal Percentage infers you will use this valve to modulate flow, not just two-state full open or shut


    ^ suggests the remainder of the piping system is ignored.
    Sounds like homework to me. How does your reference define 'equal percentage" ?

    see also http://www.documentation.emersonpro...rticlesreprints/headleyrev_spr03_valvemag.pdf
  7. Jul 30, 2015 #6
    It just states that the differential pressure is constant. I'd assume this would mean that with each difference there will be exactly 10% between them. Finding the change in flow rate from one interval to the next. Not sure if that helps at all...
  8. Jul 30, 2015 #7

    jim hardy

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    have you yet defined "equal percentage" ?

    A quick google search took me to a page that has this example problem worked out in excruciating detail...

    we expect you to show some effort.
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