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"Gas flow through irregularities in surface finish"


I have a small aluminium chamber filled with compressed nitrogen at approx. 240 bar. A steel ram is pushed up into the chamber. The ram has a rubber O-ring around it to make a seal + prevent the gas leaking out. However, some gas is still leaking out... Would irregularities in the surface finish of the aluminium provide channels for this leakage?

If so, then I'd like to model the flow using equations for flow through a circular pipe - what would be a sensible diameter of 'theoretical pipe' to use? i.e. what sort of fraction of Ra?

Kieran Gillick
Cambridge university - Cambridge, UK


Hi Kieran,

Yes, imperfections in the bore could cause some mini leaks but why just a SINGLE 0-ring? Even (far lower psi) control valves may have as many as four or more 0-rings.

I know nowt about the properties of 'rubber' at those ultra high pressures. Are you SURE you are using the right material? Does hysteritis play a role?

Re your other questions, sorry, I can't help you.

freeman newton portrait
Freeman Newton [dec]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).


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