By Dongyeop Shin (November 2024) 

Modern aerospace engineering depends on a wide array of components to ensure safe and efficient operations, with precision seals being among one of the most critical. When you combine precision sealing solutions that adhere to stringent aerospace sealing and manufacturing standards, the results minimize maintenance, prevent leaks, reduce weight, and avoid catastrophic failures - protecting aircraft and launch vehicles and the lives who take flight. The path to qualifying components and equipment for aviation and space programs is often challenging due to the time-consuming and rigorous process.

Polymer and metal seals in aerospace systems, i.e., aircraft engines, hydraulic systems, fuel systems, and environmental controls, maintain pressure, temperature, and fluid control, ensuring the reliability of numerous critical components. Due to the harsh environment of aviation and space operations, seals must endure extreme temperatures, pressures, and exposure to aggressive chemicals. Incorporating Omniseal Solutions’ materials and components in aerospace applications provides many technology advantages.

• Preventing Leaks: One of the primary functions of seals is to prevent the leakage of fluids like fuel, oil and hydraulic fluids, as well as gases such as air and nitrogen. Proper functioning of various systems can be ensured while protecting our environment from potential contamination.

• Maintaining Pressures: Seals are a vital part in maintaining necessary pressure levels, especially in high-pressure systems like hydraulic and fuel systems. By keeping pressure consistent, seals optimize performance and efficiency in these demanding applications.

• Handling Temperature Ranges: Aerospace seals must operate in a wide range of temperatures, from the freezing conditions of high altitudes to the extreme heat of jet engines. Materials must consistently maintain their properties and performance across this temperature spectrum.

• Excluding Contaminants & Chemical Exposure: Aerospace seals are exposed to aggressive chemicals, including hydraulic fluids, fuels, lubricants, and cleaning agents. They must resist chemical degradation to maintain integrity and performance and be a barrier against contaminants, e.g., dust, dirt, and moisture. Keeping harmful substances out of critical systems protect sensitive components from damage, thereby enhancing the longevity and reliability of the entire system.

• Reducing Friction & Wear: Seals also help minimize friction and wear between moving parts. By providing a protective barrier, they not only extend the lifespan of components but also improve overall efficiency, contributing to smoother operation and better performance.

• Vibration & Movement: As with the automotive industry, aircraft and space components are subject to constant vibration and movement. In dynamic applications, at least one surface is in motion relative to the other. A typical example is a hydraulic cylinder with a shaft and a bore. Further, there are two directions of motion in dynamic applications: reciprocating or linear motion, and rotary (including oscillating) motion. Omniseal Solutions offers mostly radial seals (rod and piston seals) in such applications. Whether radial or axial (face) sealing is required, the seals must be flexible and durable to accommodate these dynamic conditions without losing their sealing capabilities.

• Weight Considerations: In aerospace applications, every gram counts. Seals must provide excellent performance without adding unnecessary weight to the aircraft in order to reduce fuel costs – a must for aviation and space customers.

1. Aerospace Standards (AS)

• AS9100D: Aerospace Quality Management Standard ensuring product safety, reliability, and regulatory compliance. It is a critical standard for MRO organizations (Maintenance, Repair, and Overhaul) in the aerospace industry, ensuring that maintenance processes meet the stringent requirements for safety, quality, and regulatory compliance in the aviation sector.

• AS1234: Though primarily focused on elastomeric seals, AS1234 includes performance testing guidelines relevant for all aerospace seals. It covers high-temperature and high-pressure environments, which are critical areas where spring-energized seals and rotary lip seals excel, especially those made from polytetrafluoroethylene (PTFE), or other advanced polymers.

• AS1895: AS1895 provides general requirements for hydraulic seals, focusing on the materials and performance characteristics needed to maintain integrity in aerospace hydraulic systems. Spring-energized seals, particularly those used in dynamic hydraulic applications, must meet these general standards to ensure system reliability and safety.

• AS4052: AS4052 provides material specifications and testing requirements for dynamic seals, including the material resilience needed for aerospace fluid power systems. Since spring-energized seals are often made from PTFE or other advanced polymers for aerospace use, this standard ensures that the materials meet the necessary thermal, chemical, and mechanical resistance requirements.

• AS4716: While AS4716 primarily deals with O-rings and dynamic elastomeric seals, it includes specifications for groove dimensions and tolerances for seals in aerospace hydraulic and pneumatic systems. Since spring-energized seals often fit into similar applications, this standard can be relevant for defining the installation environment, particularly groove design and surface finish.

• AS4832: AS4832 also specifies the test procedures and performance criteria for seals used in high-temperature, high-pressure applications, particularly in the aerospace industry. The standard is crucial for ensuring the reliability and safety of seals utilized in critical aerospace systems, such as engines and propulsion systems.

2. Aerospace Recommended Practices (ARP)

• ARP1231: Testing guidelines for high-temperature seals in aerospace, focusing on durability under extreme conditions.

• ARP5316: Instructions for storage, handling, and shelf life of elastomeric seals to ensure long-term reliability.

3. MIL Standards (Military Standards) (Some examples only)

• MIL-DTL-25988: Covers fluorocarbon elastomer materials for seals in military aircraft, ensuring performance in extreme environments.

• MIL-STD-1523: Age control requirements for elastomeric seals and gaskets to ensure long-term performance.

• MIL-G-5514: Specifications for high-performance hydraulic and pneumatic seals, capable of withstanding temperature variations and long-term wear.

• MIL-PRF-5606, MIL-PRF-83282: Military specifications for hydraulic fluid used in aircraft, military aircraft, and other aerospace applications. 

• MIL-PRF-87257, MIL-PRF-7808, MIL-PRF-23699: Outlines the requirements for specific types of lubricant, particularly for use in aerospace applications.
   

4. SAE AMS (Aerospace Material Specifications)

• AMS7276: Material requirements for PTFE (polytetrafluoroethylene) seals, valued for chemical resistance and durability in aerospace applications.

• AMS7257: A specification developed by SAE International that covers the requirements for a high-strength, corrosion-resistant alloy known as austenitic stainless steel. Specifically, AMS 7257C refers to a specific type of stainless steel that is often used in aerospace and other demanding engineering applications.

• AMS5510: This specification covers the properties of certain grades of stainless steel (like 304 and 316) that are commonly used for sealing applications.

• AMS6381: This standard specifies the requirements for nickel-copper alloys, which can also be relevant for seals used in corrosive environments.

• AMS4970: This specification pertains to titanium and titanium alloys, which are sometimes used in sealing applications due to their strength-to-weight ratio and corrosion resistance.

• AMS2680: This is related to the properties of elastomeric materials used in conjunction with metal seals, which can also impact the overall sealing solution.

• AMS-P-83461: High-performance elastomeric seals for hydraulic and pneumatic systems.

5. ISO & ASME Standards

• ISO 4287: Surface roughness parameters essential for ensuring seal performance through controlled surface finish quality.

• ISO 9001:2008: Global quality management standard, focusing on consistent product quality and customer satisfaction.

• ASME B46.1: Guidelines on surface texture, critical for maintaining the integrity of sealing components.

The above is not an exhaustive list and merely highlights some of the more well-known standards for sealing and material solutions. Omniseal Solutions is a long-standing partner with established Tier 1 and Tier 2 aviation customers that require specifications and material designations that are unique to their application or system. Each customer has different needs, and they need to be consistent. Adhering to standardized requirements ensures reliability, functional commonality, and operational compatibility between systems. This is one of the most business critical aspects when it comes to making a product or solution!

For specific standards that your components need to conform to depend on the material composition, application environment, and performance requirements of the required seals. Omniseal Solutions’ engineers can help you determine what may be essential with a wide range of custom components, e.g., Omniseal® spring-energized seals, rotary lip seals, metal boss seals, bearings, and more. Put together, these standards are the backbone of safe, reliable aerospace operations, with high performance expected under the most extreme conditions.

Recent advancements in sealing technologies and material science enable manufacturers to create custom designed seals and components that can withstand the extreme conditions typical of aerospace environments.

• Cutting-edge materials: High-performance materials like fluorocarbons, polytetrafluoroethylene (PTFE), polyether ether ketones (PEEK), and PFAS-Free* polymers ensure durability under extreme temperatures and chemical exposure. Along with precision components, Omniseal Solutions provides high-performance materials that are included in the top tier of the polymer pyramid.

  • Rulon® Fluoropolymers: This material solution is commonly used for aviation applications such as track liners and actuators as it offers low coefficient of friction, high wear life, excellent abrasion resistance, chemical inertness, and ability to operate in extreme temperature and pressure ranges. Since the early 1950s, Omniseal Solutions has been the exclusive developer of this proprietary material. 

  • Meldin® Thermoplastics: These injection moldable materials can be found in helicopter nose landing gear, airplane jet engines and APUs as engineered shock strut bearings, sliding rings, bushings and piston rings, providing mechanical integrity, high thermal resistance, dimensional stability and low weight versus metal.

  • Meldin® Polyimides: These materials exhibit high dimensional stability at high temperatures and longer life at higher loads and speeds, which makes them ideal as sealing rings in flight controls or structural parts in aircraft. 

  • Hycomp™ Composites: This polymer solution is used very often due to its lightweighting properties, good thermal oxidative stability, and compatibility with all aviation lubricants. More than half of the materials used in large aircraft today are composites, such as engine, flight control, landing gear, and wheel and braking systems. Solutions vary from bushings, guide rings, wear liners, seals, clamps, and thermal isolators.

    * PFAS-Free here means we do not intentionally add PFAS material in the product, but it does not exclude the possibility of traces, as these materials are common in the environment.

     

• Innovative design: 3D modeling allows for seals to be designed with precision fit and optimized performance.

• Rigorous testing: Seals are subjected to comprehensive testing protocols, including fatigue, pressure, and thermal cycling tests, ensuring reliability in real-world conditions.

Omniseal Solutions goes beyond conventional testing by developing custom test rigs and numerical simulations to evaluate seal performance under your specific application’s conditions – another service provided to your business to meet the highest standards of safety and reliability.

Aerospace seals are critical components that enable those in the aviation and space industries to reach higher heights, proven to solve unique challenges, including extreme temperatures, high pressures, chemical exposure, and constant vibration. Using precision sealing solutions that follow stringent aerospace sealing standards is a successful path to optimal performance of your aviation and space systems, maximizing safety and reliability. With advanced materials, innovative designs, and rigorous testing protocols, manufacturers can develop seals and components that enable safe and efficient flight today as well as tomorrow. As Omniseal Solutions stays informed on the latest sealing standards and innovations, they can maintain their decades long record of safety and efficiency across all aerospace operations. 

If you need more information on aerospace sealing standards,

• Visit organizations like SAE International for comprehensive guidelines.

• Explore regulatory bodies such as the FAA and EASA for compliance updates.

• Access technical publications and research reports for the latest industry developments.

You can also contact our experts at [email protected] for personalized guidance. Let’s work together to go beyond to make the skies safer and explore the wonders of space.