Profile: All Seals, Inc. is a full-line stocking distributor of standard & non-standard seals and rubber parts. Our teflon back-up rings are designed to prevent extrusion in rubber O-ring sealing systems. Rubber O-rings generally serves as effective seals for dynamic and static applications in hydraulic and pneumatic systems equipment. The primary reason for the use of a back-up ring is to reduce the clearance gap on the low pressure side of an O-ring or similar type seal.