Back Up O-Rings are implemented when your primary seal is subject to high temperatures or pressures, or if an excessive extrusion gap is presented in the application. They serve to provide extra strength to the seal and prevent your primary seal from being damaged. Whenever possible two back-up rings should be placed, one on each side of the primary seal. For more information, please see: Common O-Ring Materials, Comparison Properties Chart, PTFE Encapsulated O-rings, Material Shelf Life, and O-ring Groove Design Chart.
The O-ring is the most widely used seal in the industry. It is easy to install, may be used as a double-acting seal and can seal pressures of up to 800 PSI. With pressures over 800 to 2,000 PSI, backup rings should be considered for higher pressures.
The o-ring is typically used as a reciprocating seal, not for rotating shaft applications (Lip seals should be used for rotating shafts). O-rings are typically sized by their inside diameter and cross section, and are further specified by the type of compound used. For O-ring sizes other than standard sizes, specify the actual dimensions desired for the inside diameter (I.D.) and the cross section (W). There may be a tooling charge for such non-standards