Backup Rings Overview

To view dimensions of all American Standard Sizes for Backup Rings, see our Backup Ring Size Chart.

backup ringsIn a sealing application, backup rings provide added extrusion resistance, and prevent damage to O-rings and seals when subjected to high pressures, larger extrusion gaps, and/or high temperatures.

Extrusion failure is one of the most common types of O-ring failure. When the internal pressure of an application becomes too great, the O-ring will actually extrude into the clearance gap. This extrudate will quickly be nibbled away causing a loss of material, and once sufficient material is lost, seal failure will quickly follow.

There are three options to prevent this, the first of which is to reduce the clearances to lower the extrusion gap. This is obviously an expensive option, so a cheaper solution is to raise the durometer of the O-ring. Even though a higher durometer O-ring offers superior extrusion resistance, this is often not a feasible solution due to material availability, and to the fact that harder durometer materials have limited low pressure sealing ability. The last and best option is the addition of a backup ring. A backup ring is a ring of hard, extrusion resistant material such as high durometer nitrile, Viton (FFKM), or PTFE.

A back-up ring is designed to fit between the O-ring and the extrusion gap and prevent the extrusion of the O-ring. Depending upon the direction of pressure in the sealing application, you can either use 1 backup ring or 2 backup rings. If unsure, it is always best to use two backup rings per 1 o-ring.

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Contoured Backup Rings

At Global O-Ring and Seal, we stock contoured elastomeric back-up rings in Nitrile 90 Durometer and Viton 90 Durometer. We can also provide contoured backup rings in other materials.

N8-90 – Nitrile 90 Duro Contoured Backup Rings

V8-90 – Viton 90 Duro Contoured Backup Rings

Teflon (PTFE) Backup Rings

We also offer a large selection of PTFE Backup Rings including; Solid (uncut), Single Turn (scarf cut), and Spiral (multiturn) PTFE Backup Rings.

STS – Solid Teflon Backup Rings
ST – Split Teflon Backup Rings
SP – Spiral Teflon Backup Rings

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Backup Ring Size Chart

The chart below gives the metric and inch dimensions for the most common AS568 sizes of backup rings.

NOTE: The “A” dimension, or Axial Height, applies only to the rubber contoured backup rings. PTFE backup rings are flat, so they do not have this contour.

DASH # ID (in) WIDTH (in) THK (in) A (in) ID (mm) WIDTH (mm) THK (mm) A (mm)
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