The Backup ring likely found its roots in the use of leather packings, where leather was used as the sealing device in glands prior to the use of O-Rings.
The O-ring provided a much better seal compared to leather. However, the leather often filled the extrusion gap allowing for larger gaps.
The persistent problem that engineers faced was how to take an O-ring that operated optimally in close extrusion gaps, and extend its service with widening extrusion gaps.
The answer was the Backup ring.
The first Backup ring devices were made from materials like leather.
Leather did two things to help the O-Ring: it filled the gap, and continued to lubricate the O-Ring during dry running conditions. You can still occasionally find some old style hydraulic systems using leather back-up rings.
Our modern hydraulic systems often find O-rings operating at extreme pressures, with the use of Backup rings made from a variety of materials like Teflon® or filled PTFE materials.
Polyester Elastomers like Hytrel®, Nylon, PEEK, and other high modulus materials are compatible both in pressure and temperature applications.
These Backup ring devices can take on many forms such as solid rings, split rings and spiral wound Backup rings.
Where there are extreme pressures and high temperatures you may find cammed Backup rings with varying materials to protect the O-ring, while at the same time closing the extrusion gap allowing extreme pressures in excess of 100 KPSI (690 KPA).
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