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.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Space Environments: FEP-Encapsulated Helical Spring O-Rings for Cryogenic Sealing

FEP-encapsulated helical spring O-rings, a testament to engineering resilience, are redefining what engineers can expect from cryogenic sealing in space environments.

In aerospace and launch systems, where seals must endure everything from deep vacuum to cryogenic propellants, failure is not an option. Traditional elastomeric seals become brittle and unreliable at the extremely low temperatures encountered in space missions. As a result, engineers require sealing solutions that combine resilience, chemical resistance, and consistent performance under punishing conditions.

This article explores why FEP-encapsulated helical spring O-rings have become a trusted sealing solution in cryogenic aerospace systems. We’ll examine the challenges of sealing in space, the features that make these O-rings ideal for such environments, and where they are being successfully deployed in today’s launch vehicles and propulsion systems.

The Challenge of Cryogenic Sealing in Space

The unique conditions of spaceflight, including exposure to cryogenic fluids such as liquid oxygen (LOX), liquid methane, and liquid hydrogen, present a set of stresses that would compromise or destroy traditional seals. These fuels are stored and transported at temperatures approaching -420°F (-250°C), far beyond the performance limits of most elastomer-based seals.

In addition to cryogenic exposure, seals in launch vehicles must contend with extreme pressure variations, from storage tanks at 100 psi to turbopump outlets exceeding 15,000 psi; thermal shock, when materials are rapidly heated and cooled during startup and shutdown; vacuum conditions, which amplify outgassing and increase the risk of material degradation; and supercritical fluid handling, where fluids behave as both gas and liquid while demanding perfect sealing to avoid leakage or combustion risks

In such conditions, even minor leakage can result in fuel loss, combustion instability, or total system failure. Elastomeric seals, regardless of their chemical resistance, will become brittle and prone to cracking under such extreme cold. Additionally, traditional O-rings can suffer from compression set, losing their sealing force after only a few cycles of use.

Why FEP-Encapsulated Helical Spring O-Rings Work

FEP-encapsulated helical spring O-rings are designed for use in the hostile environments of space. Each seal consists of a stainless steel flat-wound helical spring core, typically made from 302 stainless steel, completely encapsulated in a seamless FEP (fluorinated ethylene propylene) jacket. This design marries the best of both worlds: a chemically inert outer surface and a mechanically resilient inner spring.

Benefits of the FEP Jacket

The FEP jacket brings several benefits:

  • Cryogenic durability: FEP maintains flexibility and integrity at ultra-low temperatures
  • Chemical resistance: Inert to LOX, liquid methane, hydrogen, and most aerospace-grade fluids
  • Non-stick surface: Minimizes friction and reduces the risk of contamination or particulate generation
  • Low permeability: Offers excellent barrier properties in vacuum and supercritical conditions

Benefits of the Helical Spring Core

The helical core adds to that with its own special (and critical) features:

  • Consistent sealing force: The spring applies uniform pressure, compensating for material deformation or wear
  • Resistance to compression set: Unlike elastomers, the spring does not relax or lose force over time
  • Temperature resilience: Maintains performance across broad thermal swings—from cryogenic fill to engine ignition

The result is a sealing solution that withstands cryogenic storage tanks, turbopump manifolds, and LOX feed systems, delivering predictable and repeatable performance, even after multiple thermal cycles.

FEP-Encapsulated Helical Spring O-Rings for Aerospace and Rocket Systems

The value of FEP-encapsulated helical spring O-rings becomes clear when examining their deployment in real-world space systems. These seals are frequently found in:

  • Cryogenic valve assemblies, where they prevent leakage at pipe junctions, manifolds, and fill ports
  • Turbopump flanges and housings, which handle rapid pressure increases and thermal fluctuations
  • Fuel and oxidizer feed lines, including stage separation and preburner systems
  • Supercritical fluid interfaces, where precise sealing is critical for performance and safety

Their use is particularly valuable in systems that transport or isolate LOX, LH2, or RP-1 (refined kerosene) in Kero-Lox and Metha-Lox configurations. In these systems, preventing cross-contamination between oxidizers and fuels is crucial, as premature mixing can lead to instantaneous ignition or explosion.

Additionally, FEP-encapsulated designs align with the industry’s push toward lightweight and low-maintenance components. Because they do not require lubrication and offer long service life, they reduce mass and complexity in the vehicle’s overall sealing strategy.

Conclusion

Sealing in space is not a job for off-the-shelf elastomers. It demands materials and designs that can withstand vacuum, cryogenics, pressure spikes, and chemically aggressive media without losing integrity. These O-rings meet these requirements and then some.

The combination of a chemically resistant FEP jacket and a load-maintaining helical spring core in these O-rings makes them ideal for aerospace systems where performance and reliability are non-negotiable. Whether you’re designing for LOX manifolds, liquid hydrogen feed lines, or cryogenic stage separation, these seals deliver the peace of mind that only proven engineering can provide.

For custom-engineered helical spring O-rings designed to thrive in spaceflight conditions, contact Advanced EMC Technologies. Our team has the experience, materials, and manufacturing capabilities to deliver high-performance sealing solutions for the most extreme environments in the universe.