What Is a Rotary Lip Seal?

cranked shaft image by Sergey Goruppa from Fotolia.com

A rotary lip seal fits between a rotatable shaft and the housing around it. The housing is relatively flat and has a hole through which the shaft extends. The seal ensures a tight fit between the parts.


Traditional rotary seals are mechanical seals between a space and two parts, and are considered relatively expensive and large. Rotary lip seals are used to replace regular rotary seals in some applications because they are less expensive and smaller.


Rotary lip seals contain lubricant inside a reservoir surrounding a rotating shaft. The short, flat seal remains stationary and rides against the shaft. Engineers discovered that lubricant will not leak much past the lip if the slope of the seal is sufficiently large.


Often made of hard rubber, rotary lip seals utilise a flexible lip that slides to engage a rotating shaft. An elastic support band provides the tight fit with the shaft necessary to contain lubricating liquids.