For single acting high pressure O-Ring applications, a back up ring will prevent O-Ring extrusion.
Double acting high pressure O-Ring applications require a back-up ring on either side of the O-Ring to prevent extrusion.
Parker’s Parbak® back-up rings help prevent extrusion in high pressure service and compensate for loose fitting parts. The use of loose fitting parts makes for cost reduction in the machining of unit components.
Anti-extrusion rings made from tetrafluoroethylene are impervious to oils and solvents. Acids and inorganic salts have very little effect on PTFE resin. In addition to its good chemical resistance, PTFE may be used over a wide temperature range, from below -73°C to over 204°C (-100°F to over 400°F). Thus, PTFE back-up rings may be used with most elastomeric O-ring seals. For installation, PTFE back-up rings are supplied either scarf or spiral cut as shown in images above. These discontinuities may contribute to seal damage due to biting and pinching. PTFE can also impair seal lubrication by plating rubbing surfaces with PTFE resin to which lubricating oil will not adhere.
Back-Up Ring Tips:
- Wherever possible use two back-up rings, one on each side of the O-ring.
- If only one back-up ring is used, the O-ring should be placed between it and the source of pressure.
- Back-Up Rings should be installed with the contoured face against the O-ring, but reversal does no harm.
- Back-Up Rings will not “collapse” or cold flow if used with proper groove designs.
- Use groove widths given in the Static O-Ring Sealing and Dynamic O-Ring Sealing Sections.