O-rings are very common components in all kinds a machinery used to, say, keep a fluid from leaking from one side of a piston to another inside a cylinder. But why exactly are O-rings tori? Why are they not designed so that the contact side of the ring to the cylinder wall is flat? Wouldn't this give a more secure seal?

  • $\begingroup$ Think about what happens to the shape when under pressure. $\endgroup$
    – joojaa
    Mar 7 '18 at 20:38
  • $\begingroup$ There are seals for some shafts that are rectangular in section : designed to go into grooves and fitting them can be a challenge ... One agricultural tractor (Case International 6cyl turbo) had two of those seals on the pto shaft : needed to use a thin shim to get past the first groove to the second without slicing it... $\endgroup$
    – Solar Mike
    Mar 7 '18 at 21:13
  • $\begingroup$ @joojaa I can't really say.. It compresses? $\endgroup$
    – S. Rotos
    Mar 8 '18 at 8:41

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