What is an O-Ring?
From a sealing standpoint, two characteristics make an o-ring - the shape and the material of construction. The shape is a circular torus or doughnut-shaped ring. Primary dimensions - the inner diameter (ID), the outer diameter (OD) and the cross-section (CS) - are required to completely specify the size of an o-ring.
The materials used in o-rings for sealing are elastomers. Elastomers are synthetic or natural materials with resilience or memory sufficient to return to their original shape after a major or minor distortion. Other materials, such as PTFE, nylon or even metal, can be fashioned into the circular torus shape, but for the purposes of this book, the term o-ring will only be used to describe an elastomeric circular torus.
What is an O-Ring Seal?
An o-ring seal has two basic components:
- The o-ring
- The enclosed space that both compresses and contains the o-ring
The compression (or more accurately the deformation) of the o-ring provides part of the sealing function. An additional sealing function is realized when the o-ring is activated by the pressure of the gas or liquid that the o-ring serves to contain.
The containment ensures that the sealing function is maintained by keeping the o-ring where it needs to be.
The majority of o-ring seals can be categorized into one of the three following physical arrangements.
- For male gland seals, an o-ring is installed in a groove that is machined into the OD of the "piston". The piston and the installed o-ring are then inserted into the bore. The o-ring seals radially.
- For face seals, an o-ring is installed in a groove that is machined into a flat face around a hole. A second flat face then seals against the o-ring. The o-ring seals axially.
- With female gland seals, an o-ring is first installed into a groove that is machined into the ID of the bore. The rod is then inserted into the bore through the o-ring. The o-ring seals radially.
Dan Visscher
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