O-ring Materials and Applications


Early O-rings were generally made from Natural Rubber, this was great in the beginning for leak prevention, but limited the applications they could be used on. Since the 1940s a much larger selection of compounds has been developed. The development of these compounds has led to greater temperature resistance, pressure resistance and improved physical properties that are able to resist chemical reactions. 

Custom Hydraulics and Design stocks multiple different O-ring material types and sizes. Listed below are some of the materials that you will find in our warehouse on any given day

NBR, Nitrile, and Buna-N are all the most widely used O-ring materials, they are inherently resistant to hydraulic fluids, lubricating oils, transmission fluids, and non-polar petroleum based products. However, though Nitrile is great for hydraulic applications, it has a low resistance to sunlight, ozone, and weather.

Nitrile is Good For:
- General Purpose sealing
- Petroleum Oils, Fluids
- Silicone greases, Oils
- Water, water-oil emulsions, water glycol fluids
- Etheylene glycol base fluids
- Di-ester base lubricants

Nitrile is BAD for: 
- Polar solvents
- Brake fluids
- Strong Acids 
- Ozone, UV exposure

HNBR, Hydrogenated Nitrile often fills the gap between NBR and FKM elastomers its perfect for applications requiring high temperature resistance, high tensile strength, and resistance to petroleum oils. HNBR O-rings offer improved resistance to sour gas and ozone effects and have been developed to meet temperatures of -30°F – 330°F.

Hydrogenated Nitrile (HNBR) is Good for:
- Petroleum oils and fluid
- Sour gas
- Amine\oil mixtures
- Oxidized fuels
- Steam, up to 347F

Hydrogenated Nitrile (HNBR) is BAD for:
- Polar solvents
- Chlorinates and nitro hydrocarbons

XNBR, Carboxylated Nitrile is significantly greater than standard nitrile o-rings. By adding Carboxy to Nitrile the resistance to abrasion is greatly improved, 3-5 times greater than HBNR. While maintain oil and solvent resistance. XNBR O-rings provide high tensile strength and good physical properties at temperatures between -40°F – 250°F.

Carboxylated Nitrile (XNBR) is Good for:
- Petroleum oils and fluids
- Water, water-oil emulsions, and water-glycol fluids.

Carboxylated Nitrile (XNBR) is BAD for:
- Polar Solvents
- Chlorinated and nitro hydrocarbons

FKM, Flurocarbon O-rings were introduced in the 1950s and have become a crucial part of the o-ring materials family because of the broad chemical compatibility and temperature range. FKM O-rings are often used in applications that require harsh chemical and ozone resistance with temperature range between -20°F – 400°F

Flurocarbon (FKM) is Good for:
- Petroleum oils and fluids
- Di-ester bas lubricants
- Silicone fluids and greases
- Halogenated hydrocarbons
- Selected phosphate ester fluids, NOT Skydrol
- Acids

Flurocarbon (FKM) is BAD for:
- Polar Solvents
- Chlorinated and nitro hydrocarbons
- Amines
- Low molecular weight esters and ethers
- Hot hydrofluoric or chlorosulfonic acids
- Skydrol fluids

EP, Ethylene Propylene, Provides great resistance to heat, water, steam, ozone, and sunlight while providing high resistance to the affects of brake fluids, alkali, mild, acidic, oxygenated solvent environments, and outdoor weathering. Typical temperature range for Ethylene Propylene O-rings are -60°F – 250°F.

Ethylene Propylene (EP) is Good For:
- Skydrol
- Water, water-glycol fluids, steam
- Silicone oils and greases
- Dilute acids and alkalies
- Polar solvents
- Alcohols
- Automotive brake fluids

Ethylene Propylene (EP) is BAD for:
- Petroleum oils and greases
- Di-ester based lubricants
- Aromatic fuels
Hydrocarbon solvents

SBR, Styrene Butadiene, was originally developed as a replacement for natural rubber in tire, SBR O-rings are a low cost general purpose elastomer. Providing resistance for many polar type chemicals, ketones, and alcohols. Styrene Butadiene o-rings are widely accepted for the use in automotive brake fluids and has a temperature range of -50°F – 212°F.

Styrene Butadiene (SBR) is Good for:
- Automotive brake fluids

Styrene Butadiene (SBR) is BAD for:
- Petroleum oils and fluids
- Hydrocarbon solvents
- Strong acids
- Ozone

IIR, Isobutylene Isoprene Rubber, commonly referred to as “Butyl” is compatible with water, steam, alkalis, oxygenated solvents, and phosphate ester fluids with a temperature range of -65°F – 250°F. Butyl also offers excellent resistance to gas permeation, vacuum applications, ozone, and outdoor weathering. In most applications Butyl, has been replaced by Ethylene Propylene.

Isobutylene Isoprene Rubber (IIR) is Good for:
- Phosphate ester bas fluids
- Polar solvents
- Silicone fluids and greases

Isobutylene Isoprene Rubber (IIR) is BAD for:
- Petroleum oils and fluids
- Di-ester based lubricants

CR, Polychloroprene , commercially called Neoprene are general purpose elastomers it is characterized by its limited resistance to petroleum oils and oxygen. Neoprene o-rings have great aging characteristics in ozone and water along with resistance to alkalis, abrasion, flex cracking, and acids. Making CR O-rings suitable for petroleum, animal, and vegetable oils. Furthermore with a broad temperature range of -45°F – 250°F and excellent adhesion qualities to metals. Because of Neoprene o-rings moderate costs and benefits it is desirable in many applications.

Polychloroprene (CR) is Good for:
- Refrigerants
- High aniline point petroleum oils
- Mild acid resistance
- Silicate ester lubricants

Polychloroprene (CR) is BAD for:
- Strong acids
- Polar solvents
Chlorinated, aromatic, and nitro hydrocarbons

VMQ, Silicone , O-rings are made from silicone, oxygen, hydrogen, and carbon and are best suited for applications with temperature extremes. With a temperature range that is -94°F – 400°F silicones provide outstanding resistance to compression set, sunlight, ozone, oxygen, moisture, and fungus. Because of the degree of cleanliness found in silicone elastomers it is often the preferred o-ring for food and medical applications because they are non-toxic. Silicones are not recommended for dynamic sealing applications and are highly permeable to gasses.

Silicone (VMQ) is Good for:
- High-aniline point oils
- Dry heat
- Chlorinated di-phenyls

Silicone (VMQ) is BAD for:
- Polar solvents
- Acids

FVMQ, Flurosilicone, combines the high and low temperature ranges from silicone with the fuel and oil resistance of fluorinated elastomers and you have a temperature range of -75°F – 400°F. Precautions should be in place to avoid fluid degradation which causes the production of acids to attack flurosilicone. FVMQ feature resilience properties and resistance to ozone and weathering. Most times you will see FVMQ used as static seals in a fuel system or in a dry heat application the may involve exposure to petroleum oils.

Fluorosilicone (FVMQ) is Good for:
- Petroleum oils and fuels
- Di-ester based lubricants
- Silicone fluids and greases

Fluorosilicone (FVMQ) is BAD for:
- Brake fluids
- Hydrazine
- Polar solvents

ACM, Polyacrylate, O-rings offer a temperature range of 0°F - 350°F and are resistant to oxidation, ozone, aliphatic solvents, sunlight, weathering, gas permeation, and flex cracking, Polycrylate o-rings are typically found in automotive automatic transmissions and power steering applications using type A fluid.

Polyacrylate (ACM) is Good for:
- Petroleum oils
- Automatic transmission fluids

Polyacrylate (ACM) is BAD for:
- Alcohol
- Glycols
- Alkalis
- Brake fluids
- Chlorinated and aromatic hydrocarbons

FEP, PTFE, is a durable chemically inert polymer with a temperature range of -300°F – 450°F. It features great weather, ozone, and chemical resistance, coupled with good tensile strength, elongation, impact resistance, and low friction. PTFE should be limited to static and slow intermittent dynamic applications because of its poor elastic memory and tear resistance. Extra care should be used during the handling and seal installation to avoid nicks and scratches in the O-ring that could present leaks.

PTFE (FEP) is Good for:
- Petroleum oils and fuels
- Polar solvents
- Xylene

PTFE (FEP) is BAD for:
- Dynamic sealing applications

AU, EU, Polyurethane, offers great abrasion resistance, elongation, compression sets, and tensile strength with a temperature range of -60°F – 225°F, Polyurethane O-rings are recommended for sealing high hydraulic pressures for solutions where highly stressed parts are subject to wear and tear.

Polyurethane (AU, EU) is Good for:
- Petroleum oils and fuels
- Mineral oils
- Weak acids and bases
- Aliphatic solvents
- Alcohols
- Ether

Polyurethane (AU, EU) is BAD for:
- Concentrated acids and bases
- Polar solvents
- Strong aromatic compounds
- Brake fluids
- Water or steam

We hope that through this blog post we could clear up some of the confusion around what seal type to use and what type seal is best for hydraulic applications, or any application for that matter. If you found this helpful and are looking for more head over to our blogs to see what other knowledge we at Custom Hydraulics and Design have created.