Back-up Rings are pure hard rubber piece with concave on one side relative to the o-ring shape, having no intended sealing function. Instead, as their name indicates, they are protective and supporting elements made from extrusion-resistant materials. They are installed in a groove together with an elastomeric sealing element preferably with a corresponding O-Ring, in both dynamic and static applications, to prevent extrusion of the O-ring when it is subject to high pressures or elevated temperatures. Elevated temperatures (160° F and higher) impose a severe burden on the physical and mechanical properties of rubber O Rings which further increases their tendency to extrude. Two back-up rings should be used with one on each side of the primary seal. Due to the tight fit of the Back-up Ring in the housing, they prevent extrusion of the pressurised elastomeric sealing element into the sealing gap.

A system of a rubber seal and a properly selected and installed back-up ring is shown to be often significantly more efficient in terms of fluid leakage than the seal without the back-up ring. The most important function of the back-up ring is to improve the seal's resistance to damages through extrusion into the clearance on the seal's low-pressure side. The ability to provide such resistance depends on the material properties of the back-up ring, the cross section dimension of the seal and the back-up ring as well as the clearance size, pressure and temperature. It is normally an advantage to use rod seal types with an integrated back-up ring. The back-up ring will then follow the radial movements of the rod since it is affected by the pressure of the hydraulic fluid transmitted through the central sealing ring material. An integrated back-up ring is not subjected to mechanical loads.


- Use of O-Rings in high pressure applications
- Use of O-Ring materials with a low hardness
- Compensation of radial sealing gaps
- Use for internal and external sealing applications
- Reciprocating and rotating movements possible
- Compensation for large temperature fluctuations
- Static and dynamic applications