Orings

O-rings are torus-shaped seals used to prevent the passage of fluids or gases between mating surfaces. They are seated in a groove and compressed to form a seal, functioning in static and dynamic applications. The cross-section is circular, and the inside diameter is sized to fit the sealed component.

Materials used for O-rings are diverse. Elastomeric compounds such as nitrile rubber (NBR), fluorocarbon (FKM/Viton), EPDM, silicone, and neoprene are common, with PTFE used in some specialty applications. Specialty grades offer enhanced chemical resistance, temperature tolerance, or wear performance. Standard sizes and tolerances for O-rings are defined in international and regional standards such as ISO 3601 (metric) and AS 568 (inch).

Design and use considerations include chemical compatibility, temperature range, and operating pressure. Dynamic seals must endure sliding friction, while static seals rely on sustained compression. Proper gland design provides adequate squeeze to prevent extrusion and accommodates expected pressures. Groove width and depth must be matched to the chosen cross-section, and typical compression for many elastomer grades ranges roughly from 15% to 30%.

Manufacturing and installation considerations are important for reliability. O-rings are molded or machined to tight tolerances. During installation, care is needed to avoid nicking or cutting the seal; compatible lubrication can help. Poor seating, misalignment, or improper gland geometry can lead to leaks, extrusion, or compression-set failures.

Common failure modes include thermal and chemical degradation, compression set, extrusion under pressure, and wear in dynamic seals. Proper material selection, gland design, and installation practices are essential for long-term sealing performance.