Radial shaft seals, also known as lip seals, are used to seal rotary elements, such as a shaft or rotating bore. Like other seals for fixed parts, prevents the penetration of liquid through the hole, in thise case through the hole through which the shaft passes. Along the inner side of the radial shaft seal which is closest to the shaft there is an annular spring, which puts pressure on the shaft and thus prevents liquid penetration regardless of the shaft rotation.
