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Rubber Seal Types and Designs

Updated on January 25, 2011

Rubber seals are mechanical seals widely used in both dynamic as well as static sealing applications to prevent fluid leakage between two mating surfaces. These seals are generally made from natural and synthetic elastomers. The flexible nature of the seals, unlike adhesives, makes them ideal for use in a number of industries, including construction, automotive, and aerospace. Other prominent features of rubber seals that have led to their widespread adoption is the resistance to aging and adequate flame retardation ability. The variety of rubber seals available in the market are categorized based on their design and materials. The design-based category includes O-rings, X-rings, square rings, and U-cup seals - each type with a distinct cross section. Butyl, nitrile, and silicone are the commonly used materials to manufacture these rubber seals.

An O-ring is a doughnut-shaped gasket with a circular cross section. Made of elastomeric compounds such as natural or synthetic rubber, these rings perform sealing action by deforming to take the shape of the cavity and guarantee a predetermined interference fit. O-rings are normally divided into static and dynamic seals. While static sealing applications have little or no relative motion between the mating surfaces, dynamic sealing applications involve definite relative motion between the surfaces. O Ring seals are widely preferred for machine design as they are inexpensive, reliable, and have simple mounting requirements. O-rings are available in both standard and custom sizes.

Rubber seals with profiles shaped like the letter-X are called X-rings. Also known as quad rings or Q-rings, these rings are primarily designed as a better alternative to standard O-rings, particularly in rotary seal applications. The four-lobed design of these rings provides a double-sealing action, which is far more effective than sealing with a conventional O-ring. A major advantage of the four-lobed configuration is that it prevents the seal from twisting within the groove. As X-rings are provided with two sealing areas, they require less deformation to maintain an effective seal when compared to an O-ring. Less squeezing will reduce friction, which in turn will improve the service life of the ring. Above all, X-rings prevent leakage that often results due to the parting line's irregular surface found in an O-ring. X-rings are produced with the same dimensions as corresponding O-rings.

Square rings:
Just like O-rings, square rings are rubber seals with square cross sections, particularly suited for high pressure gasketing functions. Also known as square-cut or lathe cut rings, these seals are produced from a wide range of elastomeric and thermoplastic materials. Similar to X-rings, square rings can also be used as a direct replacement for similarly sized O-rings or other deformation-type molded seals. In static applications, the sealing performance of the square rings is superior to corresponding O-rings. However, lathe-cut square rings perform poorly in dynamic sealing environments because they lack accurately formed edges, controlled surface smoothness, hardness, and the elasticity of molded o-rings.

U-cup seals:
Another type of rubber seal is the U-cup seal, typically used for sealing rods or rams and is ideal for applications having small gland spaces. They have U-shaped cross sections and both their inside and outside diameters are self-sealing. The three common varieties of U-cup seals are rod U-cups, piston U-cups, and symmetrical U-cups.

Rod U-cup seals are rubber seals in which the sealing action is performed by its inner lip and typically used for sealing between piston rods and casings. These seals, provided with improved lip design, are capable of preventing shrinkage and low temperature leakage problems. Piston U-cups, on the other hand, are used for sealing between the piston and cylinder wall. Here the sealing action occurs on the outer lip of the seal. These seals are provided with sufficient preload condition to prevent interference with the cylinder wall due to thermal expansion at high operating temperatures. Symmetrical U-cup seals can be used in both rod and piston sealing applications and are produced with equal lip interference and equal heel clearance on both the inside as well as outside diameters. The tips of these seals are knife trimmed to eliminate mold flash and provide effective low pressure sealing.

To locate suppliers worldwide of rubber seals, including O-rings, X-rings, U-cups, and more, check out the O ring manufacturers page at Zycon.


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      Nori Murthy (NVSN Murthy) 

      8 years ago

      This article is informative and educative, I sincerely thank the team for their excellent efforts in spreading this rare knowledge to the people of our planet.

      NVSN Murthy (Nori Murthy), Independent Researcher, India.

      A temporary visitor on earth serving industry supporting life on earth / email:


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