Back-up rings are installed to prevent the extrusion of an elastomeric O-ring in its housing groove under certain operating conditions.
Back-up rings are usually manufactured in virgin PTFE. Other filled PTFE and Plastics are also available depending on the application. They are also available in NBR and Viton 90.
Spiral back-up rings enable the back-up ring to be opened with ease for fitting over a shaft, and ensures the O-ring is supported around its entire diameter.
Solid single turn back-up rings can also be supplied, and these are usually endless to ensure good support. However, they can be scarf split if required.
Contoured Rubber/Par Backs
Contoured Back-Ups are routinely produced in a 90 durometer Nitrile and Viton. This provides sufficient elasticity to permit stretching over the major diameter of a piston and then snapping back into the gland groove cut into the piston. 90 durometer has sufficient hardness to resist extrusion of the softer elastomeric O-Ring performing the actual sealing function against the high pressure liquid or gas.