Elastomeric seals have potential disadvantages:  chemical attack, swelling, degradation, heat aging, compression set, and high friction.  However, the addition of a spring and the careful selection of an elastomer can virtually eliminate many of these problems. 

Spring-energized seals have a U-shaped groove in which a corrosion-resistant metal spring (usually made of stainless steel) is placed. Once the seal is seated in the gland, the spring is compressed and applies a force on the gland that seals the surfaces.  This creates a tight barrier to prevent leakage of gas or fluids.  A common material used with spring-energized seals is Polytetrafluoroethylene, referred to as PTFE or Teflon.  This polymer further enhances the properties of spring-energized seals.  In fact, there are five specific benefits to energized PTFE seals!

Compression Set

When elastomeric materials remain under a load for an extended period of time, there can be issues with permanent deformation, or set.  This can be serious a problem for seals, causing a decline in sealing force over time.  Spring-energized seals eliminate the problem of compression set.

Degradation under Harsh Conditions

The spring provides elasticity that does not degrade under chemical attack.  One of the issues with using an elastomer seal is selecting a material that provides the correct mechanical properties while at the same time remains compatible with all the fluids that the seal may come in contact with.  By using a spring-energized seal, the selection of the elastomeric material is simplified because the spring provides much of the strength and elasticity needed.   The use of PTFE provides excellent resistance to chemical attack, good performance for both static and high-speed applications, and a wide service temperature range.

High-pressure Performance

When pressure is increased, the seal becomes even tighter because of the compression of the spring within the seal.  This means that an increase in pressure results in an increase in the strength of the seal itself.

Friction

One thing that makes PTFE special is that fact that can be used in either dry or lubricated conditions. In fact, PTFE has an extremely low coefficient of friction on its own.

Conclusion

Spring-energized PTFE seals are an excellent approach to avoid compression set, escape degradation under harsh conditions, perform well as pressure increases, and provide low friction without requiring lubrication.

For a free troubleshooting guide and design considerations charts download a free copy of Polymer Sealing Troubleshooting Guide.

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