What is an O-Ring - by Patriot Fluid Power


An O-ring, also known as a packing or a mechanical squeeze seal, is a torus or doughnut shaped ring with a round cross-section. They are generally molded form an elastomer such as a rubber compound, however, O-rings are also made from PTFE (Teflon®) and several other thermoplastics as well as metals.

O-rings are one of the most common hydraulic and pneumatic seals used in machinery design due to the fact they are easy to manufacture, are very inexpensive and have relatively simple mounting/installation requirements.


O-rings were first patented May 12, 1896 by Swedish inventor J.O. Lundberg. The US patent was filed by machinist, Niels Christensen in 1937. He used the O-ring as a component in a hydraulic braking system and described it as “a circular section ring . . . made of solid rubber or rubber composition”.

After migrating to the United States in 1891, Christensen patented an air brake system for streetcars. Later the US government commandeered the O-ring patent During World War II and classified it as a critical war-related item thus giving the right to manufacture to other organizations.


O-rings are used primarily for sealing but are also used as a lighter-duty mechanical belt drive. They can be used in static (motionless) as well as dynamic applications (motion between parts). O-rings have been tested in certain applications to seal up to 5000 psi. The maximum sealing pressure of an O-ring will depend on the seal durometer (hardness) and the diametrical clearance between the mating parts.

They have a temperature range between -50f up to +650f for rubber elastomers and as high as +1600f for O-rings manufactured using metal compounds.

O-Ring Applications - by Patriot Fluid Power

Some common applications for O-rings include hydraulic cylinders, pneumatic cylinders, pumps, motors, valves, hose fittings, fluid or gas sealing, vacuum sealing, and many other custom and standard applications.

If you have any questions about o-rings or seals you can contact Patriot Fluid Power anytime.

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