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Pressure Loss over Time

  1. May 2, 2013 #1
    Greetings All,

    I have a question regarding Pressure Loss through a Small hole vs Time.

    My simplified scenario is that I have a vessel filled with Sea Water Pressured up to 70 bar. At the outlet valve, there is a pressure release port of 5mm dia which is able to relieve the pressure down to 3 bar is a matter of 3 seconds.

    To describe the scenario better, only after the pressure has been released can the valve be opened fully.

    Question:- How long will it take if i increase the Pressure release port to say 10mm. I would like to make the pressure release even faster. Is there a direct relation of rate of pressure release to size of hole??

    Am unable to find anything regarding this topic.

    There is a similar thread but cannot make anything out of the response there.


    MAny Thanks & Regards.
  2. jcsd
  3. May 2, 2013 #2


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    Staff: Mentor

    It will depend on your setup. If the pressure drop in your port happens over a short length (<5mm), it should be a reasonable assumption that mass flow is proportional to the area. In that case, doubling the diameter should give 1/4 the original time. This assumes that the opening process does not need any time...
  4. May 5, 2013 #3

    thank you for your quick reply. i would have to confirm that the port length is very short.
    COuld you please quote some reference where you get the assumption of mass flow rate and area?
    Or if there is a formula i could refer to?

  5. May 5, 2013 #4


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    Staff: Mentor

    For short ports, the exit velocity is determined by the pressure difference (and the shape of the port), but not the area. Every textbook about fluid mechanics should cover that.
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