An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface.
O-rings are one of the most common seals used in machine design because they are inexpensive, easy to make, reliable and have simple mounting requirements. They have been tested to seal up to 5000 psi (35 mega pascals) of pressure. The maximum recommended pressure of an O-ring seal depends on the seal hardness and gland clearance.
Material matters. Due to this, selecting an o-ring material for a specific application is dependent on many criteria, including what’s being sealed, temperature range, pressure, dynamic or static service, desired service life, installation considerations, tolerances and many more. General purpose compounds are used broadly, however, utilizing the exact compound consistently is equally as important. At Global O-Ring and Seal, you can be assured that all our general purpose o-rings meet the standards stated in our spec sheets. We do not mix compounds even for general purpose o-rings. To learn which o-ring materials will work best in your application, review our Material Selection Guide.
The O-ring may be used in static applications or in dynamic applications where there is relative motion between the parts and the O-ring. Dynamic examples include rotating pump shafts and hydraulic cylinder pistons. Static applications of O-rings may include fluid or gas sealing applications in which: (1) the O-ring is compressed resulting in zero clearance, (2) the O-ring material is vulcanized solid such that it is impermeable to the fluid or gas, and (3) the O-ring material is resistant to degradation by the fluid or gas.
Determining durometer isn’t hard. The hardness of rubber compounds is measured by the Shore A durometer; the higher the durometer, the harder the compound. In addition, softer compounds stretch easier and seal better on rough surfaces. Harder compounds offer greater abrasion resistance and resistance to extrusion.