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AS568 O-Ring Information

O-Ring Design Information

What is an O-Ring?

An O-Ring is a torus or donut-shaped part of circular cross section made of an elastomeric (rubber) material. O-Rings function as low-cost, compact, reliable and forgiving sealing devices for liquids and gases. Because of the resilience of the elastomer, O-Rings absorb tolerance stack-up on the metal parts they seal.

How do they seal?

An O-Ring blocks the gap between two closely spaced surfaces by its memory or tendency to return to original shape when deformed. Normally, the O-Ring is installed in a gland that consists of a rectangular groove and a facing surface. By design, the O-Ring is squeezed into the gland during installation and the resulting force provides sealing at low pressure. As pressure is increased, it is transmitted through the O-Ring to mating surfaces thus augmenting seal effectiveness.

All O-Ring applications can be classified into two basic types:

  • Dynamic, where there is relative motion between the parts of the gland (a reciprocating rod or piston seal)
  • Static, where the two parts of the gland do not move relative to each other (such as a pipe flange).

O-Ring design parameters:

The proper design for the application of an O-Ring seal falls naturally into two main areas, dimensions and material selection.

Dimensions of both the O-Ring and the gland in which it is installed depend on:

  • The size and shape of the parts to be sealed
  • The pressure to be contained
  • The type of motion, if any

Material selection, that is, the choice of the specific The O-Ring Store LLC O-Ring compound, depends on:

  • The fluids to be sealed
  • The temperature of the application
  • The pressure to be contained
  • The type of motion, if any
  • Material specifications, if any

Design steps The design of an O-Ring application falls logically into seven basic steps:

  1. Select the elastomer
  2. Select a standard size
  3. Determine the maximum gap
  4. Specify gland dimensions
  5. Check for installation
  6. Select the specific The O-Ring Store LLC compound
  7. Select the The O-Ring Store LLC part number