Back Up Ring

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Back-up rings help prevent extrusion in high pressure service or compensate for loose fitting parts. The use of loose fitting parts makes for cost reduction in the machining of unit components.

The 90 durometer curve may be used to find the maximum recommended clearance at a given pressure for temperatures up to 74oC. In using these curves, it must be remembered that cylinders tend to expand when pressurized. The extrusion curves can be used in 2 different ways to reap the benefits of backup ring, depending on the application. In low pressure seals, the curves will indicate wider permissible clearances than those given in the design charts. Tolerance on these can be opened up until they permit these larger clearances to occur, resulting in substantial machining economies. When tolerances are increased, however, one must check to be sure that squeeze values cannot become too high or too low.

In high pressure applications, the curves will indicate whether adding a backup ring will permit the use of standard catalog gland dimensions or whether the clearance will need to reduced further.

In double acting seal assemblies, a backup ring is required on both sides of the O-ring. It is cheap insurance to use 2 backup rings even in single acting installations.

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