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Cryogenic seals are required in a variety of industries, including LNG fueling systems, specialty gas manufacturing, cryo coolers, radio astronomy, scientific instrumentation, pharmaceutical research, and many more.  One of the most reliable sealing solutions for cryogenic applications are polymer spring-energized seals.  In this blog post, we are going to review spring-energized seals and then discuss what the recommended spring configuration is for cryogenic applications.

Helical-Spring.jpgSource


Review of Spring-Energized Seals

One of the popular solutions for sealing cryogenic materials is the use of spring energized seals.  In this type of seal design, the lips of the seal are pressed against the mating surface by a spring.  This provides a tight seal even in adverse circumstances.

The spring itself is most typically manufactured from 17-7 precipitation hardening stainless steel or 301/304 stainless steel, although in some applications you may see Hastelloy, 316 stainless steel, Inconel, or Elgiloy.  The seal jacket is most often a polymer, with the three most popular choices for cryogenic applications being PTFE, TFM, and UHMW-PE.  These polymers work very well in the cryogenic range of temperatures while providing low friction, chemical compatibility, reliability, and dimensional stability.

Spring Design

Besides the jacketing material, the most important aspect of designing a cryogenic spring-energized seal is the type of spring used. The most common designs are cantilevered, helical, angled coil, full contact, and ribbon. While some of these designs may look similar to each other, such as helical and angled coil or cantilevered and ribbon, each one has its own set of ideal applications due in part to how the load is distributed by the spring.


For sealing challenges involving cryogenic temperatures, most experts will recommend the use of helical springs.


For sealing challenges involving cryogenic temperatures, most experts will recommend the use of helical springs. The spring element in this design is a simple helical spring and it works well for both rotary and static applications, as well as those involving reciprocating motion.  For oscillatory or static motion, consider using a solid spring design.  Both of these also support high pressures and vacuum pressures (which often go hand-in-hand with cryogenic temperatures).

Conclusion

Spring-energized seals are an excellent option for achieving a reliable, tight seal in cryogenic temperatures.  For cryogenic applications, the most highly recommended spring configuration is the helical spring.  It provides excellent sealing power at extreme temperatures and works for both static and dynamic applications.

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