O-ring seals are a round cross sectioned sealing device available in a variety of materials (elastomers) and standard AS568A, metric and Japanese Industrial Standard (JIS) sizes. Some of the most common elastomers appear below along with some application and chemical resistance data.
The standard AS568A size chart is available in the downloads section of this website.
SQUARE CUT O-RINGS have a square cross section and utilizes the same standard AS568A size chart that the round cross section o-ring uses. The square cut o-rings are typically stocked in NBR.
QUAD RINGS, sometimes called double seal o-rings, have four sealing surfaces that provides twice the number of sealing surfaces when compared to that of a standard O-ring. NBR quad rings are available in standard AS568A sizes.
BACK UP RINGS are typically made from NBR 90A, FKM 90A or PTFE. Configurations include solid, split, spiral and contoured. All configurations are available in standard AS568A sizes and some metric sizes. Back up rings are designed for high pressure applications to prevent the o-ring from migrating into the sealing gap.
Common O-ring Elastomers
General descriptions are provided below for some of the more common o-ring sealing elastomers. Further information regarding compatibility with specific chemicals can be obtained in the chemical compatibility tables here or in the PDF Library.
NBR / NITRILE / BUNA 70A Duro & 90A Duro
NBR is the most commonly used material for o-rings because of its good mechanical properties, its resistance to lubricants and greases and its relatively low cost.
Standard grades of NBR are typically resistant to mineral oil-based lubricants and greases, many grades of hydraulic fluids, aliphatic hydrocarbons, silicone oils and greases and water to about 80°C (190ºF).
NBR is generally not resistant to aromatic and chlorinated hydrocarbons, fuels with a high aromatic content, polar solvents, glycol-based brake fluids and non-flammable hydraulic fluids (HFD). NBR also has low resistance to ozone, weathering and aging.
Nitrile is recommended for:
- General purpose sealing
- Petroleum oils and fluids
- Silicone greases and oils
- Di-ester based lubricants (MIL-L-7808)
- Ethylene glycol based fluids (Hydrolubes)
CR / NEOPRENE 70A Duro
Neoprene is moderately resistant to both petroleum oils and weather (ozone, UV, oxygen). Neoprene is classified as a general purpose elastomer which has relatively low compression set, good resilience and abrasion, and is flex cracking resistant over a temperature range of -40ºF to +225ºF.
Neoprene is recommended for:
- Refrigerants (Freons, ammonia).
- High aniline point petroleum oils.
- Mild acid resistance
- Silicate ester lubricants
EPDM / ETHYLENE PROPYLENE 70A Duro
EPDM materials generally have a high resistance to hot water, steam, aging and chemicals, and are suitable for a wide range of application temperatures. They are divided into sulfur-cured and peroxide-cured types. Peroxide-cured compounds are suitable for higher temperatures and have much lower compression sets.
EPDM has won broad acceptance because of its excellent resistance to phosphate ester type hydraulic fluids. Ethylene propylene has a temperature range from -65° to +300°F (-54° to +150°C) for most applications.
EPDM materials are completely unsuitable for use with all mineral oil products—lubricants, oils, fuels.
EPDM is recommended for:
- Phosphate ester based hydraulic fluids. (Skydrol, Fyrquel, Pydraul)
- Steam to +400°F (+204°C)
- Silicone oils and greases
- Dilute acids
- Dilute alkalies
- Ketones (MEK, acetone)
- Automotive brake fluids
FLUOROCARBON / FKM (Viton®) 75A or 90A Duro Black or Brown
FKM materials are noted for their very high resistance to heat and a wide variety of chemicals. Other key benefits include excellent resistance to aging and ozone, very low gas permeability and the fact that the materials are self-extinguishing.
Standard FKM materials have excellent resistance to mineral oils and greases, aliphatic, aromatic and chlorinated hydrocarbons, fuels, non-flammable hydraulic fluids (HFD) and many organic solvents and chemicals.
FKM materials are generally not resistant to hot water, steam, polar solvents, glycol-based brake fluids and low molecular weight organic acids.
Fluorocarbon is recommended for:
- Petroleum oils.
- Di-ester based lubricants (MIL-L-7808, MIL-L-6085)
- Silicate ester based lubricants
- Silicone fluids and greases.
- Halogenated hydrocarbons (carbon totrachlorido, trichloroethylene).
- Selected phosphate ester fluids.
SILICONE 70A Duro
Silicone materials offer outstanding temperature resistance across a broad range from -80ºF to +400ºF. Silicone materials provide excellent resistance to sunlight, ozone, oxygen, UV light, and moisture. Silicone materials are physiologically harmless so they are commonly used by the food and drug industries. Silicone offers poor tensile, tear, and abrasion resistance and is not recommended for use in dynamic applications. Silicones are generally not resistant to fuels, aromatic mineral oils, steam (short term to 120°C possible), silicone oils and greases, acids, or alkalis.
Silicones are recommended for:
- High-aniline point oils
- Dry heat
- Chlorinated di-phenyls
FLUOROSILICONE 70A Duro
Fluorosilicone elastomers have the same mechanical properties as silicone but are resistant to solvents, fuel, and oil (similar to Viton®). The primary uses of fluorosilicone materials are in fuel systems at temperatures up to +350°F (-i-177°C) and in applications where the dry-heat resistance of silicone is required but the material may be exposed to petroleum oils and/or hydrocarbon fuels. The high temperature limit for fluorosilicone is limited because temperatures approaching +350°F may degrade certain fluids producing acids which attack the fluorosilicone elastomer.
Fluorosilicone is recommended for:
- Petroleum oils and fuels.
Polytetrafluoroethylene (PTFE), Teflon®
PTFE is a completely fluorinated polymer that is the most chemically resistant polymer available. PTFE can withstand a very wide temperature range from -300ºF to +500ºF. It is inert to most chemicals and solvents with very few substances that degrade the material (notably fluorine, chlorine trifluoride, and molten alkali metal solutions). PTFE is also very slippery and repels virtually everything making it perfect for applications that require a high coefficient of friction. PTFE is not crossed-linked like a regular elastomer and therefore has poor elastic memory, can deform under constant compressive load and can be damaged during installation.
PTFE is recommended for:
- Excellent resistance to almost all chemicals
- Not subject to aging, so a near infinite shelf / storage life
- Can be use in food, chemical and medical industries
- Low elasticity (memory)
- Low coefficient of friction