In an oil seal environment there is a shaft that is rotating inside a housing or bore. Because of friction, there must be some clearance between the shaft and the bore. The function of the oil seal is to stop whatever fluid is inside from leaking out the clearance between the shaft and housing. The seal may also be used to prevent outside materials, such as dirt, from moving in through the clearance.
An oil seal normally consists of three basic components: the sealing element, the metal case and the spring. The purpose of the sealing element is to stop the fluid from leaking between the shaft and housing. The metal case will give rigidity and strength to the seal while it is being held in the bore or recessed groove. The spring will help make the sealing element more effective. All materials must be selected depending on the environment in which the oil seal will function.