Other seal type choices include U-ring or block vee ring, V-ring, clearance or labyrinth seals, and bearing isolators. U-ring or block vee ring seals are also called U-packings or Block Vee packings. Depending on their construction, U-rings and block vee rings can be used as a rod seal, a piston seal or a symmetric seal. U-rings and block vee rings are single acting, or unidirectional seals, and must be mounted back-to-back in double-acting cylinder applications.
A Block Vee seal is more compact and has better performance characteristics under high pressure than a U-ring. V-ring seals are all rubber seals used primarily to exclude dirt and other contaminants. V-rings stretch over a shaft and seal against the side of a housing or other machine component. There are many different styles of clearance, or labyrinth seals. The one thing they all have in common is that they all operate on a principle of positive clearance (i.e., no rubbing against the shaft or housing). Many labyrinth seals are comprised of a rotor (rotating) and stator (stationary) member with a radial gap between the two members. The gap must be larger than the radial clearance of the bearing being sealed. In addition, the operating speed and temperature must be considered when using a labyrinth seal. These seals generally do not perform well at low operating speeds.
Another form of labyrinth seal is a laminar-sealing ring, which uses a series of flat metal washer-like rings of varying diameters to create a labyrinth seal. Bearing isolators are dynamic seals designed to protect bearings from outside contaminants. They are comprised of a rotor (rotating) and stator (stationary) member. Some bearing isolators are of labyrinth construction while others use O-rings or other positive seals.