Polymer Backup Rings Use and Applications
Back-up Rings or Anti-extrusion rings are used to prevent extrusion of a primary seal in high pressure applications. They are most commonly seen in service with a rubber O-ring, though Back- up rings can be used in conjunction with a variety of primary sealing products i.e. energized polymer seals with a spring or O-ring acting as the energizer. Back-up Rings do not provide any sealing function. They are simply intended to reduce the extrusion gap on the low-pressure side, so that an O-ring, or whichever primary seal is being used, can fulfill its sealing function without being damaged.
When to use a Back-up Ring
A back-up ring is required in following conditions:
- The pressure on the seal is over the extrusion resistance limitation of the seal.
- Risk of damage to the seal needs to be reduced
- The extrusion gap is increased by using guide rings or wear rings.
- The seal’s extrusion resistance is reduced
Typical back- up ring materials for demanding or server service.
- Fluorolon 1000 Virgin PTFE
- Fluorolon 1025 Glass Filled PTFE
- Fluorolon 3000 PEEK
- Fluorolon 5100 Natural Nylon
- Fluorolon 5000 UHMW
Backup rings (MS28782) made of Teflon™ (PTFE) do not deteriorate with age, are unaffected by any system fluid or vapor, and can tolerate temperature extremes in excess of those encountered in high pressure hydraulic systems. Their dash numbers indicate not only their size but also relate directly to the dash number of the O-ring for which they are dimensionally suited. They are procurable under a number of basic part numbers, but they are interchangeable; any Teflon™ backup ring may be used to replace any other Teflon™ backup ring if it is of proper overall dimension to support the applicable O-ring. Backup rings are not color coded or otherwise marked and must be identified from package labels. The inspection of backup rings should include a check to ensure that surfaces are free from irregularities, that the edges are clean cut and sharp, and that scarf cuts are parallel. When checking Teflon™ spiral backup rings, make sure that the coils do not separate more than ¼ inch when unrestrained.
Materials Temperature Max. Pressure Range
-425°F to +450°F (-254°C to +232°C)
1,500 psi (103 bar) dynamic / 4,500 psi (310 bar) static