O-ring sizing rules?

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  • O-ring sizing rules?
  • TuckerUK

    Let’s say you want to replace a broken O-ring from some obscure product for which no data or manuals exist. How do you determine the O-ring diameter and thickness?

    The O-ring may have been stretched, so surely measuring the old one won’t do?

    You could measure the O-ring groove, but how much wider than the gap do you want the O-ring for efficient sealing? How much smaller than the shaft do you want the O-ring for a good seal?



    Measure the groove width and diameter and the diameter of the corresponding housing / shaft OD that you want to seal against and I’ll look it up.

    We have all of the information here at work – think I would probably get shot for giving it out to anyone but happy to look it up for you.


    Premier Icon JAG

    There are guidelines based on the pressure you’re sealing and the dimensions of the parts you’ve got.

    Stage 1) measure accurately what you’ve got
    Stage 2) estimate the pressure that you’re trying to seal
    Stage 3) Contact an O-ring supplier and either get their catalogue (which will contain the rules) or check out their website for design rules

    irelanst’s link looks like what I’m talking about 😆

    Premier Icon faint

    measure the groove dimensions, and either the shaft or bore you are sealing.
    Where did the equipment originate from America = Imperial, Europe = Metric, UK will probably be a BS number (this is not perfect but can be a good start). If it a threaded port this will limit the number of options making it easier.
    Then get on the internet and check the online catalogues, eg Forsheda, EAP Seals, to see what fits the numbers you have measured.
    EDIT must type faster


    Appears to be an offer above but feel free to email me the details I’ll give you a specification. You need to know the ID (shaft ) and OD, assuming it is a piston style seal rather than plate and bore seal. Also fluid medium (to ensure comparability, for example dot fluids eat normal seals) and working pressure (guesstimate will do).

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