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 a radial shaft seal.By Radial shaft seals, also known as lip seals, are used to seal rotary elements, such as a shaft or rotating bore.