Back-up rings are used with O-rings and seals for both static and dynamic sealingBack-up rings are used with O-rings and seals for both static and dynamic sealingapplications. They prevent extrusion of the O-ring or seal when it is subjected to highpressure. The back-up ring should be used on the opposite pressure side of the seal.For seals that are exposed to pressure from both sides, two back-up rings should beused, one on each side of the O-ring or seal.