U-Cups 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 pnuematic 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 lips 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 against the inner surface of the lips. 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 microinches. It is not recommended that U-cups or any other single lip seal be used in any application where there is excessive side loading.
The 6226 Series U-Cup has a flat sealing lip and is available in 70 Durometer Nitrile.
The lips of the U-Cup should always be toward the pressure force. The U-Cup is a floating seal which means the height of the U-Cup should be between .015" to .090" shorter than the depth of the gland. (See the Packing Space Chart below). The added gland space allows the pressure to equalize on both lips, thus keeping the U-Cup from rolling. The surface finish for a static seal surface should be 32 RMS maximum. The dynamic surface should be in the range of 8 to 16 RMS. Finishes rougher than 16 RMS could cause premature lip wear and finishes finer than 8 RMS can result in failure of the seal due to loss of lubrication.