There has oil film between oil seals and shaft which controlled by oil seal edge. This oil film has characteristic of fluid lubrication. The stiffness of oil film just can let oil file and air touch to a meniscus under the action of surface tension of liquid. It prevent the leakage of working medium for achieve the sealing of the rotating shaft. The sealing ability if oil seals will be decided by the thickness of oil film of sealing face. It will leak if thickness is big and it will occur dry friction and cause abrasion of oil seals and shaft also if thickness is small. It will cause heat and abrasion easy if there has no oil film between sealing lip and shaft.
When we install the oil seals, we need to put some oil on the seals and make sure the oil seals and shaft axis are vertical. The sealing lip of oil seals will tidy the lubricating oil up from the shaft and abrade the sealing lip serious. During operation, the lubricant in the shell seeps slightly to achieve the ideal condition of forming an oil film at the sealing surface.