Small Diameter Spring Energized Seals
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

How Spring Selection Defines Spring-Energized Seal Performance

Most failures blamed on PTFE actually originate in the spring. This blog post discusses the load-management system and key features of spring-energized seals for canted coil springs, V springs, cantilever springs, helical springs, and coil springs.

Canted Coil Springs (Slant Coil Springs)

Canted Coil Springs and Slant Coil Springs from Advanced EMC Technologies

These springs are wound so that individual coils are set at an angle to the longitudinal axis. They are highly versatile and often used for dynamic sealing applications. Their key feature of canted coil springs is the flat load curve they provide. These spring energizers generate a nearly constant force across a wide deflection range. The constant force allows precise control over friction and torque, making these spring energizers ideal for applications where these factors are critical. Canted coil springs are also unlikely to experience compression set.

Canted coil spring energizers work best in moderate to high-speed rotary applications. Beyond sealing, their unique design allows them to serve as mechanical connectors (latching/locking), EMI/RF shields, and multi-point electrical conductors.

V Springs (V Ribbon Springs)

The V spring is a general-purpose, cantilever-type energizer. They offer an excellent balance of performance and cost-effectiveness. In addition, V springs provide a moderate load over a wide deflection range. They function well in both static and dynamic applications, including those involving rotary or reciprocating motion.

V springs are frequently recommended for severe service conditions, including vacuum pressures and cryogenic temperatures. V spring energizers are often a preferred choice for harsh operating environments.

Cantilever Springs (Finger Springs)

Often referred to as finger springs, these spring energizers feature a V-shaped cross-section and are distinguished by a linear load curve, meaning the force increases linearly with deflection.

The load is concentrated at the very front edge of the seal lip, which provides positive wiping action and makes them particularly effective for exclusion and scraping applications. They also generate extremely low friction.

Cantilever spring energizers are well-suited for sealing viscous media. They are typically found in low to medium-speed applications, such as hydraulic cylinders, pumps, compressors, and shocks.

Helical Springs (Helical Flat / Compression Springs)

Helical springs consist of a wound ribbon of metal and are characterized by a high load-versus-displacement curve. Because they produce a very high unit load with a small deflection range, helical springs provide tight, reliable sealing. They are well-adapted for sealing light gases and liquids.

Helical springs are generally limited to static, slow-dynamic, or intermittently dynamic applications because friction and wear are less of a concern than seal reliability. These spring energizers are often used in pipe flanges and crush jackets where the seal must embed into surface irregularities. Experts highly recommend helical configurations for cryogenic applications.

Coil Springs (Spiral Pitch Springs)

When many people visualize a spring-energized seal, they picture this wire coil type. These spring-energizers actually perform best in high-pressure, medium-speed applications and are known for their low friction. 

Spring Materials

The performance of spring-energizers is also dependent on the material selection. The material selection is primarily determined by the chemical and thermal environments involved. At Advanced EMC, we recommend one of the following spring materials: 

  • Stainless Steel (300 Series, 17-7 PH, 301/304): Common for general-purpose and cryogenic applications
  • Hastelloy: Recommended for highly corrosive media
  • Elgiloy: Used for high heat, corrosive environments, and salt water
  • Inconel: Used in severe environments and cryogenic applications

Conclusion

When spring-energized seals fail, the problem is often not the jacket, but the spring. Knowing about load consistency, deflection behavior, and how that force is delivered over time is key to deflection, friction, wear, and whether a seal actually survives its operating environment.

At Advanced EMC, spring-energized seals are engineered as complete systems, not just components. Our team will assist you from spring selection to geometry and material pairing, aligning the seal design with real-world conditions. If you are troubleshooting a failure or designing for demanding service, contact Advanced EMC today.

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!