In hydraulic and pneumatic seals, main seals such as O-rings receive much attention, but their performance relies on an often overlooked component: the back up ring.

What is a Back up Ring?

A back up ring is a rigid ring installed next to the seal to prevent it from being squeezed into the metal gap under high pressure. Back up rings are essential when system pressure exceeds 5 MPa, preventing seal failure and system leakage.

Core Functions

Back up rings provide a physical barrier:

• Prevent seal extrusion damage
• Extend the life of the sealing system
• Improve system pressure resistance
• Enhance equipment reliability

Materials and Design

Common materials include:

• PTFE: Chemically resistant, low-friction
• Fluororubber: Resistant to strong chemical corrosion
•  

Main designs include:

• Integral
• Single-cut
• Helical

Application Areas

• Construction Machinery: Hydraulic cylinder seals
• Automotive Systems: Safety components such as brakes
• Industrial Equipment: Petroleum, chemical, and marine industries

Although a supporting role, the back up ring is crucial for the reliable operation of high-pressure sealing systems. Choosing the right back up ring is just as important as choosing the right main seal; both are indispensable for ensuring system performance.