What is the purpose of rotating shaft seals?

Rotary shaft seals keep lubricant from leaving the rotating crankshaft or other components with rotating or oscillating parts. They also prevent dirt and debris from becoming mixed with the lubricant and rotating parts.

Without rotary shaft seals, lubricants in these devices would disperse into the nearby environment, causing the operating temperature of the device to increase and the component to fail. Rotary shaft seals are used most frequently in gasoline and diesel fuel engines such as those found in automobiles, trucks, industrial machinery and ocean vessels. The rotating shaft seals are to a large degree the determinants of the lifespan of these items.