U-SEAL

For sealing purposes, the U-cup depends upon contact made by its flexible lips. The solid section at the heel of the cup is generally narrower than the packing groove width and does not come into contact with the groove base and the adjacent part until pressure is applied. Consequently, when installed, the packing is slightly pre-loaded.



U-cup packings have low frictional qualities and are completely automatic in action. Due to their design, they can be assembled satisfactorily in glands which have variations in cross sectional dimensions, thus permitting more liberal manufacturing tolerances. U-cups packings are also very successful in applications where it is desirable to reduce excessive packing friction.



Characteristics:

U-section rings are manufactured from various grades of synthetic rubbers to meet the different working conditions. The hardness will vary according to the application and pressures.



Comparatively lesser hardness (70-75° shore 'A') ranges are used for pneumatic applications, while a hardness range of 85-90° shore 'A' for hydraulic application. Homogeneous rubber 'U'seals are recommended up to a working pressure of 100kg/cm2. When the pressure exceeds 100kg/cm2, then a fabric reinforced 'U' seal will have to be used. Where higher pressure and / or excessive clearance between the reciprocating members are









involved there a fabric laminated 'U' packing has to be used.



At high pressure there is a possibility of the seal material being extruded through the clearance gap and the heel portion of the seal will be 'nicked' by which the effectiveness and life of the seal will be reduced considerably. In such cases, the use of an anti extrusion ring of tougher material such as PTFE, Nylon or acetal resin will be of added importance.