PTFE Spring Energized Seals for Cryogenic Applications
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Designing Spring-Energized Seals for Cryogenic Hydrogen Systems

Cryogenic hydrogen systems are among the most challenging to specify reliable sealing solutions for, with issues ranging from the extremely low temperatures to hydrogen permeability and embrittlement. 

This blog post explores the challenges and proposes a proven solution: PTFE spring-energized seals. And discusses how Advanced EMC can help.

Challenges of Sealing in Cryogenic Hydrogen Systems

There are several key problems that arise when specifying a sealing solution for a cryogenic hydrogen application. Four of these are discussed below.

Extremely Low Temperatures

The first issue with sealing cryogenic hydrogen is the temperature. On average, hydrogen is stored and transported at about  253 °C. At such low temperatures, conventional elastomers will lose elasticity, shrink, and possibly crack. In addition, thermal contraction will cause the seal contact pressure to drop. And just because a seal is predicted to work at room temperature, it will fail disastrously when the temperatures drop to H2 storage temperature. 

Hydrogen Permeability and Leakage Risks

Hydrogen is extremely small, with diatomic hydrogen being the smallest molecule in the known universe. This small molecular size means that  H2 can diffuse through many different materials. The resulting permeability leads to serious risks of leakage or even explosive decompression during warm-up cycles. Resolution of these issues includes sealing solutions with exceptionally high tolerance, with a seal lip material that maintains integrity even at the molecular level.

Hydrogen Embrittlement

Hydrogen embrittlement is a problem for many materials. In short, hydrogen can diffuse into metal components and make them increasingly brittle over time. This embrittlement leads to cracked metal seal housings. 

Material Compatibility

Many conventional seal materials will become unsuitable when cryogenic temperatures are reached. Examples include thermal expansion mismatches between components and a loss of flexibility, which are among the top problems. Material selection quickly becomes limited to options such as PTFE and certain fluoroelastomers because only a handful of materials can retain their flexibility, dimensional stability, and roughness at the temperatures required for handling H2.

Spring Energized PTFE Seal

Spring-Energized Seals for Cryogenic Hydrogen Systems

Spring-energized seals are advanced solutions composed of a polymer seal jacket with an internal metallic spring energizer. Because of the spring energizer, a consistent sealing force can be achieved even in the presence of issues such as dimensional shifts and contraction. 

A properly designed spring-energized seal can effectively maintain a seal in liquid H2 environments. Such a seal can handle pressure cycling and dimensional changes, and reduces friction and wear compared to conventional seals.

Here’s a summary of how a spring-energized seal with a PTFE / filled PTFE jacket addresses the challenges described thus far:

ChallengeProblemPTFE Cryogenic Seal Advantage
Low TemperaturesElastomers shrink, crack, and lose sealing force at –253 °C.PTFE stays flexible and dimensionally stable with low thermal contraction.
Hydrogen PermeabilityH₂ diffuses through many materials, causing leakage or decompression.PTFE has low gas permeability; spring-energized lips maintain tight contact.
Hydrogen EmbrittlementMetals become brittle and crack under hydrogen exposure.PTFE is immune to embrittlement and protects surrounding components.
Material CompatibilityMost materials fail due to brittleness or expansion mismatch.PTFE retains flexibility, stability, and chemical resistance at cryogenic temperatures.

Advanced EMC Spring-Energized Seals

At Advanced EMC, we specialize in PTFE spring-energized seals. We offer cryogenic-rated PTFE jackets that use corrosion-resistant metal allows, such as Hastelloy or Inconel, for the enclosed energizers. Precision engineering and manufacturing mean optimized hacket profiles for containing H2 and machining as needed to achieve an extended service life. We have developed sealing solutions for various industries, and offer tailored spring force, geometry, and material properties for spring-energized solutions.

Conclusion

Sealing cryogenic liquid H2 involves major challenges. The extremely low temperatures, hydrogen permeability, hydrogen embrittlement, and material compatibility all lead to problems that conventional sealing solutions do not address well.  Spring-energized PTFE seals, however, address these issues and more for a robust, rugged, and reliable solution.

Advanced EMC’s expertise ensures seals that meet the unique demands of cryogenic hydrogen systems, enabling safe, efficient use of hydrogen in advanced energy applications. Contact us today to learn more!

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Seals for Cryogenic Space Applications: Why PTFE Spring-Energized Seals Are the Solution

Seals for cryogenic space applications must survive conditions that push materials and engineering itself to the edge. Temperatures can drop below -250°C. There’s no atmospheric pressure. No lubrication. No margin for error. And when these seals are used in systems like cryogenic fuel transfer, attitude control thrusters, or deep-space instruments, failure isn’t just inconvenient: it’s catastrophic.

That is where PTFE spring-energized seals come in. These seals combine low-temperature flexibility, chemical inertness, and a constant, adaptive sealing force, making them one of the most reliable options for cryogenic sealing in space.

In this article, we break down how they work, what materials and energizers are involved, and why they outperform traditional sealing technologies in the vacuum and cold of space. We also tackle the biggest challenges in cryogenic aerospace sealing—and show how these advanced seals meet them head-on.

What Are Spring-Energized Seals?

A spring-energized seal utilizes a precision metal spring embedded within a polymer jacket (e.g., filled PTFE, PEEK, FEP)  to apply a continuous force against the sealing surface, ensuring reliable, low-friction sealing even under extreme temperatures, pressure variations, and material contraction. These seals have proven ideal for some of the harshest environments, including static and dynamic cryogenic systems.

Spring energizers are available in various configurations, including cantilever for light loads and dynamic applications, helical for low temperatures and vacuum conditions, and canted coil for high-pressure, high-temperature environments.

For cryogenic PTFE spring-energized seals, the most common grades used are

  • Virgin PTFE (low friction, extreme temperature tolerance)
  • Glass-filled PTFE (better wear resistance)
  • Carbon-filled PTFE (enhanced dimensional stability)
  • MoS₂ or graphite-filled PTFE (lower wear, improved dry run)
Cryogenic Seals for Low Temperature Situations
Cryogenic Seals for Low Temperature Situations

Seals for Cryogenic Space Applications: Challenges

Engineers face several challenges when specifying cryogenic sealing solutions for space applications. These include thermal contraction, outgassing, material stability, lubrication, rapid pressure transitions, and seal life.

Challenge #1: Thermal Contraction

The extreme cold in space causes both hardware and seals to contract, with traditional elastomeric seals often shrinking and losing sealing force at cryogenic temperatures. PTFE spring-energized seals maintain contact via the spring energizer as it compensates for seal shrinkage. In fact, spring energizers adapt to radial or axial changes, maintaining sealing pressure even at temperatures as low as -250°C.

Challenge #2: Outgassing and Material Stability

Materials with a high volatile content can outgas in a vacuum, leading to the contamination of optics and electronics. However, Virgin PTFE and high-purity filled PTFE variants exhibit minimal outgassing, meeting NASA/ESA standards. They are chemically inert and stable under ultra-high vacuum (UHV) conditions.

Challenge #3: Friction and Lubrication in Vacuum

In space, the lack of atmosphere can make lubrication extremely difficult (especially if vacuum pressures are involved). PTFE is self-lubricating and has one of the lowest coefficients of friction among polymers. In addition, filled PTFE (e.g., graphite or MoS₂) enhances dry-run performance and the spring-energized design ensures low breakout friction and a consistent force profile.

Challenge #4: Rapid Pressure Transitions

Systems transitioning from launch (atmospheric) to space (vacuum) face rapid pressure differential, and traditional elastomeric seals can blow out, crack, or fail to reseat. On the other hand, spring-energized PTFE seals accommodate pressure variations with a controlled energizer preload, while the elastically deforming PTFE jacket absorbs shock without sustaining permanent damage. Additionally, options are available for high-vacuum to moderate-pressure regimes.

Challenge #5: Seal Longevity and Wear

Another serious complication when designing seals for space is that maintenance is likely not possible once a system is deployed in space. Seal wear over long mission durations can lead to leakage or mechanical failure, but PTFE’s wear resistance is enhanced through fillers (carbon, glass, bronze). And the spring maintains sealing force over millions of cycles without fatigue. Advanced EMC also provides fully characterized wear data for mission planning.

Why Choose Seals for Cryogenic Space Applications from Advanced EMC?

Advanced EMC Technologies brings deep materials science expertise and aerospace-focused engineering to the design and production of PTFE spring-energized seals, especially for extreme environments like cryogenic sealing in space.

Every mission has unique sealing requirements, and Advanced EMC offers an extensive portfolio of PTFE formulations, energizer types, and precision manufacturing options to meet them. Whether the application calls for ultra-low friction, minimal outgassing, or long-term performance under high-cycle dynamic loads, Advanced EMC engineers work closely with aerospace clients to specify the right PTFE grade—virgin, carbon-filled, glass-filled, or dry-lubricant-enhanced—and pair it with the optimal spring geometry (canted coil, helical, or cantilever) for consistent seal loading across a wide thermal range.

Advanced EMC’s cleanroom-compatible production standards, vacuum-bakeout-capable materials, and helium leak testing ensure that components meet the strict demands of satellite, propulsion, and orbital systems. These seals are not only designed to function below -250°C, but also engineered for endurance under pressure transitions, vibration, and long-duration service without re-torque or adjustment.

With an emphasis on low outgassing, dimensional precision, and thermal resilience, Advanced EMC’s spring-energized seals deliver proven reliability in systems where seal failure is not an option.

Conclusion

In the unforgiving environment of space, cryogenic sealing is not just a design challenge—it’s a mission-critical priority. Seals must withstand extreme cold, rapid pressure transitions, and the absence of lubrication, all while maintaining dimensional integrity and sealing force over long durations.

PTFE spring-energized seals provide a robust and reliable solution. With their combination of chemically inert PTFE jackets and precisely engineered metallic energizers, they provide consistent performance where traditional sealing technologies fail. Whether mitigating thermal contraction, eliminating outgassing concerns, or ensuring low-friction sealing in high-vacuum conditions, these seals deliver the reliability aerospace engineers demand.

When you need seals that perform flawlessly in cryogenic space applications, turn to the experts. Advanced EMC Technologies offers custom-engineered PTFE seals tailored to meet the highest standards of thermal, mechanical, and environmental performance. Backed by material expertise and decades of field-proven results, our sealing solutions are ready to meet the demands of your next mission.