Radial shaft seals, also known as lip seals, are used to seal rotary elements, like a shaft or rotating bore. Hydraulic pump seals, axle seals, valve stem seals, or strut seals are the most common examples the average person would recognize.
Radial shaft seals are used in a variety of applications and perform two essential functions: the first is to avoid leakage through retaining the bearing or system lubricant; the secondary function is to avoid the contamination of the system by outside impacts (external particles or environmental issues).