Lip seals
Lip seals serve to protect lubricated moving parts and they do this by keeping the lubricant inside the bearing, and keeping contamination from dirt or other liquids out. The term lip seal is generally used to refer to what is correctly known as rotary shaft seals or oil seals or radial shaft seals. Oil seals are commonly used in sealing rotary elements such as hydraulic pumps and valve stems.
A lip seal is a circular sealing element encompassing either a rotating or reciprocating shaft. The lip seal excludes or includes (seals) a medium in one defined volume away from another, where leakage would be a product failure. Lip seals utilize polymeric (elastomeric or thermoplastic) materials for the sealing element. They may be wholly polymeric or supported by a non-sealing element for stiffness (metallic, thermoplastic, or thermosetting polymer). Elastomers are defined as vulcanized thermosetting high polymers that are above their glass transition temperature (Tg), a second order transition, that are essentially non-crystalline in the unstressed state and can extend at least twice their original length and return to near net shape.
Thermoplastics such as polytetrafluoroethylene (PTFE) lip seals, also known as rotary shaft seals, are relied upon more and more frequently today.
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