U-Cups Seals

U-Cups seals derive their name from their shape and are self-sealing on both the inside diameter and outside diameter. They are most often used for sealing rams or rods and are very popular due to the small gland space required. They are especially adapted to low speed, low pressure environments for both pneumatic and hydraulic cylinders. They provide an extremely smooth, steady movement because of their inherent low friction.
The seal is obtained by means of the flared, flexible libs coming in contact with the rod or cylinder wall. Clearance is provided at the heel for minimum friction. Through this design, the packing is preloaded when installed. Sealing effectiveness is increased by internal pressure of the air or fluid (hydraulic seal) against the inner surface of the libs. For continued sealing effectiveness and long seal life, the surface finish of the working surface of either rods or bores should be a maximum of 16 micro-inches. It is not recommended that U-cups or any other single lib seal be used in any application where there is excessive side loading.