O-ring design and Typical applications

An O-ring also known as a packing or toric joint, is a mechanical gasket in the shape of a torus; it is an elastomeric ring of circular cross-section designed to Compressed during assembly between the parts, forming a seal at the interface.O-rings can be used in static applications or dynamic applications where there is relative motion between the component and the O-ring.Dynamic examples include rotating pump shafts and hydraulic cylinder pistons.Static applications for O-rings may include fluid or gas sealing applications, where the O-ring is compressed causing the gap to be zero the O-ring material is vulcanized to a solid so it is impermeable to fluids or gases and O-ring material resists degradation by fluid or gas.The wide range of potential liquids and gases that need to be sealed necessitates the development of a wide range of materials.O-rings are one of the most commonly used seals in machine design because they are inexpensive, easy to manufacture, reliable and have simple installation requirements.They are tested to seal up to 5,000 psi (34 MPa).Maximum recommended pressure for O-ring seals is dependent on seal hardness, material, cross-sectional diameter and radial clearance.

Theory and design 

O-rings are available in a variety of metric and imperial standard sizes.Dimensions are specified by inside diameter and cross-sectional diameter (thickness). In the US, the most common standard imperial sizes are in accordance with SAE AS568C specifications (eg AS568-214). ISO 3601-1:2012 contains the world's most commonly used standard dimensions, both imperial and metric.The UK also has standard sizes known as BS sizes, usually ranging from BS001 to BS932. There are several other sizes.

Typical applications

A successful O-ring fitting design requires a rigid mechanical mount that imposes predictable deformation on the O-ring.This introduces a calculated mechanical stress on the O-ring contact surfaces.Leakage will not occur as long as the pressure of the contained fluid does not exceed the contact stress of the O-ring.The pressure of the contained fluid is transmitted through the

essentially incompressible O-ring material, and the contact stress increases with increasing pressure.For this reason, as long as the O-ring does not fail mechanically, it can easily seal against high pressure.The most common failure is extrusion through mating components.The seal is designed to have a point contact between the O-ring and the sealing face.This allows for high localized stresses and the ability to withstand high pressures without exceeding the yield stress of the O-ring body.The flexibility of the O-ring material accommodates imperfections in the mounting component.But maintaining a good surface finish on these mating parts is still important, especially at low temperatures where the sealant rubber reaches its glass transition temperature and becomes increasingly stiff and vitrified.Surface finish is also particularly important in dynamic applications.A surface finish that is too rough will wear the surface of the O-ring, while a surface that is too smooth will not adequately lubricate the seal with the fluid film.