I work for a valve manufacturing company and our customers have an application where very large volumes of hot (200F), dry air pass through our valve. As a consequence, the rubber (carboxylated nitrile) sealing surfaces within the valve harden, eventually leading to the valve being inoperable.

While I am no polymer expert, is seems obvious to me that the plasticizers are being “cooked” out of the rubber. I am looking for a cost-effective alternative rubber material that will remain elastic/pliant in this challenging application. We offer valves that use PTFE, but this would be unacceptable to our customers from a cost perspective.

Any thoughts or guidance would be greatly appreciated.

  • $\begingroup$ PTFE isn't cost effective to your customer? Metal to metal seals worth looking at if it can work in your application. You can get class 5 air leakage on metal seats with a decent amount of polishing/lapping. Metal seals are sometimes preferred at higher temperatures (e.g. steam service) for this reason. $\endgroup$
    – jko
    Apr 27, 2021 at 16:11

1 Answer 1


TLDR: look at Viton / FKM

PTFE has poor mechanical stability, would be careful whether to use it in most sealing apps (unless it has mechanical backup). Look at other fluoroelastomers, in particular Viton (FKM) or Kalrez/Chemrez (FFKM). The other common elastomer substitutes for NBR are EPDM and silicone (PDMS). Those are the most common ones you can usually get. For "harder/stiffer" seals like compression fittings there is a wider variety with much better performance vs environment, feel free to ask.

PS - if you're using XNBR now, it suggests you may have additional needs for a dynamic sealing application. So read up on the more detailed "product selection guides" by the elastomer manufacturers, as there are specialized variants of the basic types. Also, it might be hard to avoid a cost increase.


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