What Are O-Rings? And How Do They Work?

Also known as a toric joint — in reference to its torus shape — an O-ring is a gasket with a circular-looped design that’s used to seal two working surfaces. The valve stems in automotive engines, for example, often use O-rings to prevent oil from entering the combustion chamber. The O-ring creates a air- and liquid-tight mating surface between the valve stem and the valve guide. Without this small and otherwise simple component, oil may leak into the valve guide where it’s burned inside the combustion chamber.

History of the O-Ring

The O-ring is the brainchild of J. O. Lundberg. In 1896, the Lundberg filed a patent for the circular-looped gasket. Although it was invented in Sweden, the O-ring slowly made its way across the Atlantic Ocean. In 1937, the first patent for an O-ring in the United States was filed by professional machinist Niels Christensen. What’s interesting, however, is that Christensen didn’t retain this patent.

During World War II, the U.S. government took over the O-ring patent,  describing it as a critical tool used in the Allied force’s war efforts. The U.S. government still paid Christensen for his patent, though they placed the O-ring’s design in public domain, allowing companies from the East Coast to the West Coast to produce and sell their own O-rings.

Materials Used to Make O-Rings

O-rings are available in many different materials, each of which has different properties. Some of the most common materials used to make O-rings include the following:

  • Fluoroelastomer: Often used in applications where heat is a problem, fluoroelastomer O-rings are heat-resistant, durable and long lasting.
  • Silicone rubber: Featuring a soft, spongy design, silicone rubber O-rings are used in the food service industry because they are safe and non toxic.
  • Ethylene propylene diene monomer: While not suitable for use with lubricants or fuels, ethylene propylene diene monomer O-rings offer strong resistant to moisture, steam, silicone and grease.
  • Thermoplastic polyurethane: Offering a high level of tensile strength, thermoplastic polyurethane O-rings are resistant to degradation.

Sealing Pressure

When choosing O-rings, it’s important to consider the maximum amount of pressure the o-ring can seal. O-rings are designed to naturally compress when installed between two working surfaces, which prevents air or liquid from leaking. If too much pressure is placed on an O-ring, though, it may fail. According to Wikipedia, some O-rings are capable of sealing up to 5,000 pounds per square inch (PSI). Of course, most manufacturers won’t need to seal surfaces at such high pressure, but this still attests to the sealing power of O-rings.

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