O-rings and seals are used in a wide range of industries to help you tightly seal the connections in pipes, tubes, and other elements of complex hydraulic and pneumatic systems. Due to many applications, there is also a wide variety of O-ring material choices available. Nitrile (Buna), Neoprene, Ethylene Propylene (EPDM Rubber), Silicone, Fluorocarbon (Viton), and PTFE (Teflon) are among the most commonly used compounds for O-rings and seals.
To answer many of your questions about O-rings, The Hope Group has created an advanced O-ring material selection guide, where we will look at the properties and compatibility as well as the temperature range and hardness of each O-ring material.
Factors to Consider When Picking O-rings
When picking the right O-ring for your specific application, there are many factors to consider. They include but are not limited to operating conditions, chemical compatibility, sealing pressure, temperature, durometer, size, and cost. Depending on the specific situation, you may also look at abrasion, tear, ozone, electrical resistance properties. Additionally, you can perform appropriate field tests to ensure the fluid, temperature, pressure, and environmental conditions are compatible with the O-ring of your choice.
O-ring Material Selection Guide
In order to accommodate a large variety of applications, manufacturers make O-rings and seals using various elastomers with different physical and chemical properties. Let’s look at some of them below:
Nitrile Butadiene Rubber (NBR)
Resistant to: Water, Petroleum Oils & Fluids, and Hydraulic Fluids
Not recommended for: Phosphate ester base hydraulic fluids, automotive brake fluids, ketones, strong acids, ozone, freons, halogenated hydrocarbons, and methanol
Temperature Range: -40° to +250°F, although that’s an average for the lower and upper tolerances for the various nitrile butadiene rubber (NBR) compounds manufactured by Parker. Parker’s Buna-N compound, which ranges from 70 to 90 durometer hardness nitrile, withstands temperatures from -30°F up to 250°F which includes compounds N0674
Hardness: 40 to 90 durometers Shore A
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Buna Nitrile
Most popular elastomer O-ring material. Parker Hannifin uses 70 durometer hard nitrile (Buna-N) for most of its standard O-rings supplied, with 90 durometer available for tube fittings and adapters. Seal professionals value Buna-Nitrile elastomer for competitive price and excellent resistance properties to petroleum-based oils and fuels, silicone greases, hydraulic fluids, water, and alcohols.
Ethylene-Propylene (EPDM)
EPDM has a spotless reputation in the sealing world because of its excellent resistance to heat, water and steam, alkali, mild acidic and oxygenated solvents, ozone, and sunlight (UV). Nevertheless, experts do not recommend EPDM compounds for gasoline, petroleum oil and grease, and hydrocarbon environments.
Resistant to: Extreme cold, steam, hot water, sunlight and UV, dilute acids, ketones, alkalis
Not recommended for: Petroleum base oils and di-ester base lubricants
Temperature Range: -65° to +450°F
Hardness Range: 40 to 90 durometers Shore A
Neoprene (CR)
Neoprene is a general-purpose elastomer with moderate resistance properties to petroleum oils and weather (ozone, sunlight, UV, and oxygen). Neoprene O-rings have a relatively low compression set, good resilience, abrasion, and are flex cracking resistant.
Resistant to: Refrigerants (freons, ammonia), high aniline point petroleum oils, mild acids, and silicate ester lubricants
Not recommended for: Phosphate ester fluids and ketones
Temperature Range: -45° to +250°F
Hardness: 50 to 80 durometers Shore A
Fluorocarbon (Viton)
When we talk about fluorocarbon O-rings, Viton is a popular trade name that may come into your mind. Fluorocarbon (FKM) compounds combine high-temperature resistance with excellent chemical resistance. These properties make them a popular choice for many applications, including aircraft and automotive industries.
Resistant to: Petroleum base oils and fluids, some phosphate ester base fluids, silicone and silicate ester base lubricants, acids and halogenated hydrocarbons
Temperature Range: Standards -15°F to +400°F, but some Parker FKM Viton compounds can tolerate temperatures down to –65F and up to +450F.
Hardness: 50-95 Durometers Shore A
Perfluoroelastomers (FFKM) (Parfluor)
Perfluoroelastomers (FFKM) are an extension of the Fluorocarbon FKM elastomers extending the compatibilities of the FKM while at the same time extending the upper temperature limits of the materials while compromising the lower temp limits. FFKMs are the cleanest/purest compounds available on the market. They are the first choice for clean applications and are particularly popular in the semiconductor industry.
Silicone
Silicone O-rings have many outstanding properties, including excellent flexibility and fatigue life, strong ozone, and UV radiation resistance. Despite the abovementioned characteristics, experts do not recommend silicone O-rings for dynamic applications. The low strength and poor abrasion resistance as well as high gas permeability, make them not compatible with the most petroleum fluids, ketones, water, and steam.
Resistant to: Dry heat (air to 400°F) and high aniline point oils
Not recommended for: Most petroleum fluids, ketones, water and steam
Temperature Range: -175F to +450°F
Hardness: 40-80 Durometers Shore A
Polytetrafluoroethylene (PTFE)
Polytetrafluoroethylene (PTFE) O-rings are designed to be used in harsh environments with temperatures ranging from -450°F to 600°F. PTFE O-rings are compatible with the widest range of chemicals, such as acetone, isopropyl, methyl, etc. Furthermore, they have low gas permeability and low absorption. Unfortunately, due to polytetrafluoroethylene material properties, pure PTFE O-rings are very rigid and hard to apply. Therefore, manufacturers, including Parker, solve this problem by mixing PTFE material with various fillers to provide users with more flexibility. PTFE seals are often used in food, pharmaceutical, and medical industries.
Resistant to: Most chemicals, excluding alkali metals, fluorine, a few fluoro-chemicals such as chlorine tri-fluoride and oxygen difluoride
Not recommended for: Applications requiring O-Ring stretch and compression
Temperature Range: -260°F to 300°F
Hardness: 55 to 60 durometer Shore D
