Installation of U-Shape Packings 2016-12-29T09:16:45+00:00



Fabric Reinforced U-Cups are a heavy duty seal designed primarily for slow moving rams and pistons such as found in hydraulic presses, jacks and cylinders. Space saving and ease of installation features make these unitary seals attractive to designers. They are designed with heel clearance for minimum friction and positive lip interference, which provides the initial seal at low pressures. Fabric Reinforced U-Cups are generally recommended for hydraulic pressures up to 3000 psi; however, they can be used successfully at higher pressures when clearances between the metal parts are held to a minimum.


The preferred installation for a fabric reinforced U-cup is with the use of a pedestal or pedestal and back-up cushion ring. The pedestal keeps the lips of the U-cup away jfrom teh bottom of the gland, and it does not exert radial pressure on the lips. This allows the molded-in lip interference to provide the initial seal and the pressure to actuate the lips. Pedestals are made of one or more laminations of gasket material. The length or height of the pedestal can be varied to fit the specific gland or stuffing box.

The back-up cushion ring acts as an anti-extrusion ring and protects the U-cup at higher pressures. It is usually molded of the same material as the U-cup, and since it does not function as a seal, the back-up ring may be used in split form. The use of braided filler rings is a carry-over from the leather U-cups. Leather does not have an elastomeric memory, and the braided flax filler rings were used to maintain lip contact at low pressures. Fabric Reinforced U-cups have a molded-in lip interference and the elastomer binder provides the “memory” to maintain lip contact at all pressures.


Piston Snap-On Installation

Fabric Reinforced E-cups can be economically installed on one-piece pistons. Below is a sketch of how this can be accomplished.




It is important that a sharp corner be machined where the bottom of the groove meets the shoulder. This is the secret in the success of this type of installation. For this reason it is recommended that a slight chamfer be cut in this corner, which tends to force the lip tightly in to the corner assuring that it will be retained on the piston.

Contact Us

EPM, Inc.
112 W Burke St.
Stockbridge, GA 30281

Phones and Fax Numbers

Call Free in the US: 800.659.5050
Local & International: 770.389.0501
Fax U.S: 888.353.7325
Fax Local & International: 770.389.0652