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Thread: Tension force in a fluid coupling

  1. #1
    Associate Engineer
    Join Date
    Apr 2018
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    4

    Bang Head Tension force in a fluid coupling

    I'm making a swivel joint in a pressurized air hose. I'm 99% sure that when it's under pressure, there will always be a tension on the joint of static pressure * flow area, but *someone else* is insisting that this doesn't apply if the air is flowing freely though the hose, only if the end is stopped. Fluids engineering was my weakest subject in school and that was over 10 years ago, so I'm trying to find an objective source to back me up to satisfy *someone else*. I've already done a good bit of online searching, maybe I'm not using the right search terms, or maybe it's just so obvious that nobody has a website devoted to it.

    Now that I'm thinking more about it, the area to use is probably to the inside of the first O-ring seal so it's even higher force, but that's small potatoes.

    -Harry

  2. #2
    Lead Engineer
    Join Date
    Aug 2013
    Location
    Houston TX USA
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    Unless there some special arrangement on your design, the effective and largest pressure area of any o-ring seal is its outside diameter.

    I assume that the "lower operating flowing pressure" that your associate is referring to is the fact that by Bernoulli's law the a portion of the zero flow total pressure is converted into the kinetic energy of the flowing fluid or gas; however, this reduction in static pressure due to flow is never taken into consideration in calculating the required design of any pressure containing pie, tube, fitting, etc.

  3. #3
    Associate Engineer
    Join Date
    Apr 2018
    Posts
    4
    Thanks, that's what I thought. I did eventually find this

    ESA_BAT_bolt_torque_for_flanged_connections_2012_June.pdf


    The bit on the second page referencing how the "hydrostatic end forces" work against the gasket preload on a bolted flange joint was evidence enough to satisfy the unnamed party, that and two other engineers agreeing with my assessment.

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