[TIL] 9/12/2018 O-rings, Gaskets and Seals

Today I learned the difference between O-rings, gaskets and seals.

The easiest way to tell them apart is that gaskets usually sit between two flat surfaces, and o-rings usually sit in grooves (They also have to look like Os). Seals on the other hand are anything that does not fit in those categories.

It seems like from the reading I did online, not all gaskets are elastic and compressible. As a result the re-usability for O-rings is dramatically higher than gaskets.

Failure Modes

For both gaskets and o-rings the failure modes shared are all from material properties. Since both are using elastic materials, the most common mode of failure would be from deformation. This can either be from thermal or chemical properties of the operating environment.

Design Preperation

The most important property would probably be surface finish. For O-rings it is suggested that the surface finish to stay within 32 (micro-inches) rms, or 16rms for face seals. For gaskets it seems to be suggested that 50-60Ra for aluminum and 60-100Ra by vendors. In other terms, O-rings need around 300 grit finish and gaskets need around 100 grit finish. Of course these are just ballparks, and the surface finish is specific to the method you are using. In any case you would want to prevent any cuts or scratches to be going through the area where your seal is sitting.


  1. http://profilerubber.com/gaskets-seals-orings.html
  2. https://promo.parker.com/promotionsite/oring-ehandbook/us/en/ehome/Face
  3. https://www.ljstar.com/resource/surface-finish-charts/
  4. http://www.felpro.com/technical/tecblogs/gasket-sealing-surface-finish.html

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