Loaded Lip Seal is a hydraulic U-cup, which has an o-ring or quad ring fitted into the U-shaped groove to assure good low-pressure sealing on a reciprocating shaft. Usually, the seal has a metal case, which is pressed into a housing bore and remains fixed. This seal consists of profiled elastomer ring placed in a casing, and held in place by and L-shaped metal ring. This seal is often used to seal rotary shaft of a vacuum pump.