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All Seals Incorporated
The Sealing Specialists
2110 S. Yale Street
Santa Ana, CA 92704
Phone: (714) 556-4931
Fax: (714) 557-3257


Parker 8-Dashs


Function of Teflon Back-Up Rings

Teflon back-up rings are designed to prevent extrusion in rubber o-ring sealing systems.
Rubber O-Rings generally serve as effective seals for dynamic and static applications in hydraulic and pneumatic systems equipment. One big drawback of such o-rings is their tendency to extrude into the clearance of mating surfaces when subjected to increasing pressures.

The degree of extrusion is a function of o-ring hardness, clearance of mating parts and fluid pressure.

Another variable that must be considered in determining the need for back-up rings is the operating temperature. Elevated temperatures (160 degrees F and higher) impose a severe burden on the physical and mechanical properties of rubber o-rings which further increases their tendency to extrude.

The combination of high pressures and high temperatures is a common occurrence in present day fluid systems. Moreover, the trend is toward still higher pressures and longer resident times at elevated temperatures. This places more emphasis on the role of the back-up ring in preventing o-ring extrusion.

Standard Configurations

There are three basic types of Teflon back-up rings in use: single turn (scarf cut), multi-turn (spiral cut) and solid (uncut) configurations.

Heavy Duty Back-Up Rings

Heavy duty back-up rings are configured with a greater T (axial thickness) dimension. The extra thickness provides more extrusion protection for o-rings. These rings are interchangeable with MS27595, MS28774, MS28782 and MS28783 backup rings used in MIL-G-5514 packing glands. Heavy duty back-up rings are available in solid (uncut) and in the single turn (scarf cut) configurations.

Extended Sizes

In addition to the military standards, we supply three series of extended dash-size standards which provide back-up rings for all o-rings in the Aerospace Standard AS-568A Uniform Numbering System.

These configurations have proven very useful to fluid systems designers because of the added flexibility in size selection.
Because extended sizes usually are available, industrial users are assured of the same quality and service that applies to the most sophisticated aerospace applications.

Filled Back-Up Rings

For applications where sealing systems are subjected to severe duty cycles, or where pressures exceed 3,000 psi and temperatures are above 275 degrees F, filled Teflon back-up rings are very useful.
In addition to the more common fills such as glass fibers, considerable experience with back-up rings of Nylon, Kel-F, FEP, UHMW and others. We have produced the very standards using these materials as well as more specialized compounds of Teflon.

Care should be taken to be sure that the compound chosen is compatible with the gland or rod materials of construction. There is no point in over designing components that may cure extrusions, but produce abrasion or wear problems.

  • Single Turn - MIL Standard MS28774
  • Solid, Extended Series
  • Single Turn, Extended Series
  • Single Turn, Heavy Duty
  • Solid, Heavy Duty
  • Solid - MIL Standard MS27595
  • Spiral - MIL Standard MS28782
  • Spiral - MIL Standard MS28783
  • Single Turn, Boss Connection - MIL Standard MS9058
  • Single Turn, Tube Fitting - MIL Standard MS28773
  • Spiral, Extended Series

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