Back-up rings are static seals, commonly installed with O-rings to prevent gap extrusion in static radial sealing in applications above 5 MPA. When high pressures are exerted, the soft material of the O-ring can be forced into the clearance gap, causing the O-ring to extrude. The hard back-up ring material will keep the O-ring from flowing into the gap, which will prevent premature failure. The size of the permissible extrusion gap depends mainly on the seal material, temperature and operating pressure

Back-up rings are available in extrusion resistant material such as PTFE. They are designed to fit between the O-ring and the extrusion gap and prevent the extrusion of the O-ring. The back-up ring is installed at the zero pressure side when the O-ring is exposed to pressure from one side. When the pressure comes from both sides, a back-up ring is installed on both sides. There are several types available: type S, SC, P, PC and SP.

Key properties 

• Easy to install
• Resistant to high pressure
• Wide temperature range

Applications

• Hydraulic cylinders
• High-pressure hydraulic systems
• High-pressure valves