A Guide to O-Ring Materials

Courtesy of Gallagher Fluid Seals, here’s a guide to O-Ring materials, how they are used, and when to avoid using them:

Nitrile (Buna, HBR): A widely used, economical material that has strong wear resistance and mechanical properties. Temperature: -55 to 250 degrees Fahrenheit Applications: Petroleum based oils and fuels, dynamic applications Avoid: Break fluids and ozone Hydrogenated Nitrile (HNBR): Nitrile base with added chemical strength and resistance following hydrogenation.

Temperature: -50 to 300 degrees Fahrenheit Applications: Water and steam up to 300 degrees Fahrenheit, fuel systems, oil resistant and high abrasion applications Avoid: Strong acids and polar solvents such as ethers and ketones Polyacrylate (ACM): Widely used by auto makers in power steering and transmission systems.

Temperature: -15 to 350 degrees Fahrenheit Applications: Mineral oil, engines, gear boxes, power steering, transmissions Avoid: Cold temperatures, hot water, steam Ethylene-Propylene (EPDM): Strong ozone and chemical resistance

Temperature: -55 to 275 degrees Fahrenheit, 300 degrees Fahrenheit when used with peroxide curing agents Applications: Brake systems, glycol-based fluids, H20 steam Avoid: Mineral oil products and hydrocarbon fluids Chloroprene (Neoprene, CR): The first commercial synthetic rubber developed, chloroprene has good mechanical properties over a wide range of temperatures.

Temperature: -40 to 250 degrees Fahrenheit Applications: Refrigeration, due to its excellent ozone resistance, low-temp H20 Avoid: Esters, ketones and aromatic and chlorinated hydrocarbons. Butyl: An all-petroleum compound, butyl has low gas permeability and good resistance to sun exposure and ozone.

Temperature: -70 to 400 degrees Fahrenheit Applications: Life science and medical devices, FDA applications, numerous specialized compounds for specific material certifications Avoid: Highly abrasive applications and water and steam over 250 degrees Fahrenheit Fluorosilicone (FVMQ): Broad temperature performance and strong fuel and solvent resistance, but weak abrasion resistance due to high friction.

Temperature: -75 to 400 degrees Fahrenheit Applications: Aerospace, fuel and mineral oil Avoid: High temperature air, dynamic applications Flurocarbon (Vikton, FKM): The high fluorine levels in fluorocarbon rings give them excellent swelling and permeability resistance. They also feature high temperature and chemical resistance.

Temperature: -15 to 400 degrees Fahrenheit Applications: Broad chemical resistance, transmission and blended gasoline Avoid: Low temperatures, ketones and amines Tetrafluoroethylene-Propylene (AFLAS): Excellent chemical and temperature performance.

Temperature: 15 to 450 degrees Fahrenheit Applications: Aerospace, steam, hot water, oil fields Avoid: Chlorinated hydrocarbons, ketones, acetic acid Perfluoelastomer (FFKM): Of all elastomers, this one has the highest performing temperature and chemical properties, as well as low out-gassing and extractable properties.

Temperature: -15 to 600 degrees Fahrenheit Applications: Semiconductors, chemical processing, vacuum applications Avoid: Fluorinated solvents and perfluorinated lubricants If you have questions about O-Ring materials, contact Gallagher Fluid Seals, Inc. Our experts can answer any questions you might have about these small, yet crucial, sealing products.

An O-Ring Primer

Technology is always moving forward, but some things stand the test of time. One of those things is the O-ring, which was first patented in 1896.

What is an O-ring?

A O-ring is a doughnut-shaped loop designed to prevent the passage of liquids or gases. It’s one of the simplest precision mechanical pieces ever produced, and continue to be one of the most widely-utilized sealing products.

O-rings can be made from plastic or metal, but for the purposes of our blog, we’ll focus solely on rubber – or elastomeric — O-ring design.

An O-ring, also known as a “torus,” works in tandem with the glands in which they are installed. The gland is normally cut from the metallic hardware, and works with the O-ring to seal. The gland and the O-ring must be designed together to insure top performance.

How does an O-ring seal?

Seals prevent fluids from escaping through the gaps in mating pieces of hardware. The O-ring sits in the middle of a gland when it’s at rest, but as pressure begins to rise in the sealing system, the O-ring shifts to the opposite side of the pressure.

Because the material is soft, the O-ring is mechanically squeezed to plug the hole between the two mating hardware pieces.

Limitations of O-ring use

“Although it has been stated that O-rings offer a reasonable approach to the ideal hydraulic seal, they should not be considered an immediate solution to all sealing problems.”

That was D.R. Pearl of the United Aircraft Corp. in 1947, in a paper presented at the S.A.E. annual meeting. Pearl wrote those words almost 70 years ago, but distinct limitations remain for using O-rings as a primary seal. These limitations include:
Rotary speeds above 1,500 feet per minute
Improper mating hardware design
Incompatible temperature, pressure and fluid chemical compatibility

source: http://www.gallagherseals.com/