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FKM vs. FFKM: What’s the Difference?

Fluorinated, carbon-based synthetic rubber materials, known as fluoroelastomer or FKM, emerged as a popular choice for high-performance seals in the late 1950s. FKM elastomers can withstand temperatures greater than 200°C and are still used to manufacture O-rings, seals and gaskets for automotive, aerospace, energy and other industries.

In the 1970s, DuPont™ introduced Kalrez®, a perfluoroelastomer or FFKM compound, as the gold standard elastomer for high-performance seals in aggressive media environments. FFKM has since been enhanced for even better performance and is more widely available.

The two are similar but have key differences that can lead to efficient operation or seal leaks or failure.

What is a Fluoroelastomer (FKM)?

FKM elastomers are made of fluorinated synthetic rubber that contains fluorocarbon-based polymers. This type of material offers high-quality chemical, oxygen, ozone and UV resistance. FKM can withstand operating and media temperatures up to 204°C, making it suitable for gaskets, O-rings and seals in most energy and industrial applications.

Advantages of an FKM Elastomer

  • Can withstand temperatures as low as -45 or as high as 204°C (static)
  • Highly resistant to fuels, oils, solvents and corrosive chemicals
  • Gas and liquid permeation resistant
  • High-density materials with good mechanical properties
  • Consistent seal performance and good compression

Disadvantages of an FKM Elastomer

  • More expensive than other synthetic elastomers
  • Tendency to swell with fluorinated solvents
  • Not appropriate for applications that use molten or gaseous alkali metals, ketones, esters and hot water or steam
  • Lower elasticity compared to FFKM elastomers
  • Can become brittle in extremely low temperatures

Common FKM Applications

Industrial applications: Due to their chemical stability, FKM elastomers serve as seals in pumps, valves, actuators, compressors and heat exchangers.

Chemical processing: This type of seal is ideal for protective coatings, valves and fittings that regulate aggressive chemicals.

Oil and gas: You’ll find FKM elastomers in pipelines and refinery equipment due to its ability to withstand extreme temperatures and pressure.

What is a Perfluoroelastomer (FFKM)?

FFKM elastomers have a fluorinated backbone and higher fluorine content than the FKM compound, allowing for greater elasticity. This material also offers the possibility of temperature ratings up to 325°C and nearly universal chemical compatibility, making it an ideal choice for challenging applications.

Advantages of an FFKM Elastomer

  • Can handle temperatures as low as -55 or as high as 330°C (static)
  • Superior inert properties
  • Best-in-class chemical resistance to more than 1,800 chemicals, solvents and plasmas
  • Excellent compression resistance
  • Ability to operate during temperature changes without cracking or degrading
  • Flame-retardant
  • Longevity in harsh operating conditions

Disadvantages of an FFKM Elastomer

  • Most expensive elastomer option
  • Lower mechanical strength compared to other elastomers
  • Can swell in the presence of highly fluorinated solvents
  • Requires specialized design and manufacturing
  • Restricted use in cold environments

Common FFKM Applications

Medical applications: FFKM elastomers can be used as O-rings, gaskets and seals in pharmaceutical processing due to their ability to handle aggressive agents and steam used for sterilization. They’re also ideal for semiconductor manufacturing where oxygen plasma is present.

Chemical processing: This application requires a seal with a high temperature and chemical resistance for reactor linings, valves, pipelines and pumps.

Life science: FFKM elastomers can handle sensitive and aggressive media and can be used in laboratory and bioprocessing equipment that require contamination control and sterilization.

Aerospace: FFKM seals are durable enough to be used in fuel and hydraulic systems and engine components.

Which Elastomer Material is Right for Your Application?

FFKM elastomers are slightly more versatile than their FKM counterparts and can withstand a greater range of operating conditions. Your application’s media type, temperature range, environmental conditions and compliance standards will dictate whether you need an FFKM or FKM elastomer.

FKM elastomers are typically more cost-efficient than FFKM while still providing competitive resistance features. However, FFKM is the premium choice if your application demands maximum chemical and thermal resistance.

FKM and FFKM Elastomers Available at Humphrey Products

Humphrey Products offers FKM as a temperature- and chemical-compatible sealing option for most industrial and specialty valves, including our 350 Series 2-port and 370 Series 3-port iDP aggressive media solenoid valves.

We’ve formulated an FFKM diaphragm option with our 350 and 370 Series and their inert Radel® body material to ensure our iDP valves can safely control the most difficult liquid and gas media, including reagents, chemicals, cleaners and even steam.

Trust the long-term, proven performance of FFKM parts to reduce the frequency of seal changes, lower inspection and repair costs, improve equipment uptime and increase productivity and yield. For more information, contact Humphrey Products online or call 1.800.477.8707.