In this illustration you can see the O-ring positioned in an O-ring groove.

A Teflon® back up ring has been provided to prevent the O-ring from extruding when it is subjected to high pressure

O-rings are the most popular elastomer shape used in mechanical seals. They have many advantages over wedges, U-cups, chevrons, etc:

  • They can seal both pressure and vacuum.
  • They can flex 0.003 to 0.005 inches (0.08 to 0 0.13 mm) before they roll, and then they can roll up to half of their diameter making it a lot easier for the seal faces to follow shaft run out and end play.
  • O-rings reduce shaft fretting dramatically because of this ability to flex and roll.
  • They are available in a variety of compounds.
  • Most of the O-ring compounds are available in a wide range of durometer or hardness. The average mechanical seal uses a durometer of 75 to 80 (as measured on the shore A scale), but harder durometers are available for high-pressure applications similar to those we find in pipe line sealing.
  • The O-ring configuration is usually the first shape available when a new compound becomes available from the manufacturer.
  • They are the most precision rubber part that you can purchase. O-rings are manufactured to a tolerance of ± 0.003 inches (0.08 mm)
  • You can buy them anywhere. There are plenty of distributors.
  • Unlike other shapes, most designers have settled on only a few O-ring cross sections, making spare parts and inventory a lot easier.
  • Their cost is low compared to other shapes.
  • Because they are self-energizing there is no need to spring load them to the shaft or sleeve. This means that the seal spring or springs can be designed for face loading only.
  • And finally, as a wise old man once said, “you can’t put them in backwards”.


  • On February 16, 2018