by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Seals for Cryogenic Valves

The ability of cryogenic seals to maintain integrity is often critical not just for the processes involved but for the safety of humans, other equipment, and the environment. Seal failure could lead to expensive damage, hefty lawsuits, and even loss of life. Finding reliable solutions that can handle cryogenic temperatures and the pressures involved is challenging but not impossible.

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Spring-Energized Seals for Spaceflight

With the success of commercial spaceflight companies such as SpaceX, Blue Origin, and Virgin Galactic, there is an increasing demand for high performance, dependable seals. Rockets are one of the areas where harsh environment seals are needed, but also pose extremely challenging issues for success. Spring energized seals are one solution, but why?

What Makes a Modern Rocket

Successful spaceflight involves rockets, and the primary sections of a modern two-stage rocket are the first stage engine bay, first stage, second stage engine bay, second stage, and, last of all, the payload. This constitutes the most common configuration for today’s NewSpace companies. 

Such a configuration features an expendable or reusable first stage that contains 4 to 9 engines (the number of engines varies based on company design) and an expendable second stage that typically contains a single vacuum-optimized engine. The goal of the first and second stages is to produce enough thrust to achieve a targeted orbital velocity–usually around 17,500 mph– for the payload that sits on top of the rocket.

Propellants and Pressurants

Most rockets use either solid or liquid propellant. In this blog post, the focus will be on bi-propellant rockets, which are most commonly being used or developed in the United States commercial market. Bi-propellant rockets, as the name implies, use a combination of propellants. Common propellant configurations include:

  • RP-1 (Highly refined kerosene)/Liquid Oxygen (LOX) (aka, Kero-Lox)
  • Liquid Methane/LOX (aka, Metha-Lox or Lox-meth)
  • Liquid Hydrogen/LOX (Hydro-Lox)

Pressurants and support fluids include:

  • GN2 (Gaseous Nitrogen)
  • Helium (He)
  • GOX (Gaseous Oxygen)
  • GCH4 (Gaseous Methane)

How Modern Rocket Propulsion Systems Work

For a pump-fed system, the propellants are fed from low pressure tanks into a turbopump assembly (TPA). This significantly raises the pressures to be injected into the main combustion chamber (MCC). In most cases, a small portion of the propellants are scavenged from the high-pressure side to feed a separate small combustion chamber known as a gas-generator or pre-burner and used to drive the turbine. These fuel or oxygen rich gases can then either be vented to the atmosphere or re-injected into the MCC.

Operating Conditions of a Rocket Propulsion System

Consideration of the operating conditions within a rocket propulsion system provides insight into the challenges faced by the seals.

  • State 1 – Tank to Turbopump Assembly (TPA) inlet: propellants (oxygen + methane) are usually around 50 -150 psi and RP1 will be between 20 F and 80 F while the cryogenics will be between -450 F to -260 F.
  • State 2 – TPA outlet: depending on the engine, pumps will raise these pressures to somewhere between 1,500 and 16,000 PSI.
  • State 3 – Pre-burner: pressure will have dropped across the lines and injector – usually 8-15%, however temperatures will be between 800 -1,500 F.
  • State 4: depending on the engine cycle, propellants may be in a liquid-liquid state, gas-liquid state, or gas-gas state at an array of temperatures and pressures before mixing in the MC; note that in most cases the fluids will be supercritical.
  • State 5: once across the injector, the remaining propellants will combust at temperatures higher than 4000 F while pressure in the MCC may be between 50-20% of State 2 depending on system losses; note that this pressure drops quickly as the gases are pushed toward the atmosphere.

Depending upon which stage is involved, seal requirements vary greatly but high pressures and extreme temperatures will always be involved. 

Rocket Engine Seals

Rocket engine seals must perform in some of the most harsh environments imaginable and may involve wide operating temperature ranges (including cryogenic), extreme pressures, wide thermal cycling, and chemical compatibility with fuels, propellants, and pressurants. Most importantly, they must be extremely reliable. As an example, consider the just a rocket turbopump.

The image shown is a Hydro-Lox turbopump with a geared coupling used in the Aerojet Rocketdyne RL10 engine. Where it is labeled with a 1 indicates flange locations that likely use spring-energized face seals. Downstream of the outlets  will be the main valves, and they too will most likely have additional flange connections that will require seals. Areas labeled with 2 indicate other flange locations that depend on face seals of unknown makeup but likely involve hot gas connections.

Spring Energized Seals: A Rocket Sealing Solution

One of the most reliable, harsh environment sealing solutions is the spring energized seal. Unlike conventional seals, a spring energized seal includes an energizer that enables the seal lip to stay in contact with the mating surface through extreme variations in pressure and temperature,and  dimensional changes, as well as out of roundness, eccentricity, hardware misalignment, and some degree of wear. Vibration, cryogenic temperatures, and high temperatures are also an area where spring-energized seals offer outstanding performance.

They are highly durable in operating environments where other seals simply cannot survive. In fact, the performance of such seals has been well established in aviation and aerospace, including both NASA and commercial rockets. 

A wide variety of jacket materials are available, with some of the most widely used aerospace options being PTFE (trade name Teflon) and Hytrel. Materials such as Teflon and Hytrel can handle extreme temperatures, are chemically compatible with media involved, are heat resilient, provide low friction, have excellent wear characteristics, and are typically self lubricating. In addition, both materials are available in grades that provide key characteristics such as improved wear, lower friction, additional stiffness, better strength, etc.

And the same is true for spring energizers, which vary in both geometry and material used. For example, vacuum pressure and cryogenic applications often utilize V-springs (also known as V ribbon springs), high pressure environments may use coil springs, and vacuum pressure operating conditions with medium speeds may utilize helical springs. Various materials can be used for the spring, which will be enclosed within the seal jacket; because of this, the spring material will be protected from whatever media is being sealed.

Conclusion

If you are in need of spring energized seals for space applications, allow the seal specialists at Advanced EMC help you. We have a long history of providing our customers with the seals they need, including custom engineered and manufactured solutions that not only meet their specifications but also the rigorous standards that may be involved. Advanced EMC has the design, manufacturing, and testing capabilities you need to make your design a success. Contact us today to learn more.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Benefits of Spring-Energized Seals for Wind Turbines

According to Statista, installed wind power worldwide reached a cumulative capacity of almost 743 GW (gigawatts) in 2020 and is expected to reach almost 841 GW by 2022. As it remains a competitive source of renewable energy, engineers are looking for ways to enhance the efficiency and reliability of wind farms and the turbines that comprise them. One design aspect under consideration is the seals that are used in these turbines. This week, we will discuss the various benefits of spring-energized seals for wind turbines. 

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by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring Energized Seals in the Food and Dairy Industries

The food and dairy industries are tough on seals, whether it is extreme pressures and temperatures or the limitations posed by using only FDA-approved materials. Spring-energized seals, however, can prove an excellent solution for the challenges posed by these industries. In this week’s blog post, we will discuss spring energized seals in the food and dairy industries.

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by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Best Materials for Spring Energized Seals

The polymers most commonly used in spring-energized seals are PTFE, PEEK, UHMW PE, Vitron, and Hytrel. All of these are high-performance engineering polymers, but some are better adapted for certain applications than others. In this week’s blog post, we will discuss the best materials for spring energized seals, and how they can be applied for each industry. 

Spring-Energized Seals with Polymer Jackets

Polymer sealing jackets are often chosen over their rubber counterparts for various reasons, including better performance at extreme temperatures, a wider range of chemical compatibility, and lower friction. And, depending on the material under consideration, polymers often provide better specific strength and stiffness. Because of these and other properties, they are often used as the sealing jacket for spring-energized seals.

However, knowing which polymer is best adapted for a specific application can be challenging, especially since there are a wide range of engineered polymers that offer excellent mechanical and chemical properties. What follows is a discussion of the most popular spring-energized seal materials for five industries.

Food and Dairy 

Food and dairy applications can make the design of spring-energized seals more challenging, especially when it comes to the choice of the seal jacket material. Materials must be compliant with FDA CFR 177, contained in Title 21 of the Code of Federal Regulations. And other standards may also apply, such as NSF/ANSI standard 61 for drinking water systems,  3A Dairy sanitary standards 18-03 and 20-27, and (EU) 1935/2004.

Because of such regulations, the two most commonly used jacket materials for spring-energized seals in the food and dairy industry are PTFE (both virgin and certain grades of mineral-filled) and UHMW PE (Ultra High Molecular Weight Polyethylene). Besides their FDA approval, these materials also provide low friction, compatibility with most cleaning and sanitation routines, and a good range of operating temperatures. In addition, both materials are self-lubricating, which eliminates the problem of finding a lubricant that is safe to use.

Aerospace and Defense

Aerospace and defense applications that require a spring-energized seal often turn to materials such as PEEK (Polyether ether ketone)  and PTFE. Spring-energized seals are used with hydraulic systems, fuel systems, actuators, and gimbal pods in everything from massive airliners and space rockets to lightweight, nimble drones. Operating environments may involve extreme temperatures, exposure to aggressive chemicals, and mission-critical performance. Some operating conditions may also involve cryogenic temperatures, for which PTFE and Hytrel work extremely well. Note that Hytrel is a TPC-ET thermoplastic polyester elastomer.

In space applications, temperatures can range from cryogenic vacuum conditions to extremely high temperatures and pressures. For spring-energized seals used in rockets, PTFE is the most common due to its wide operating temperature range, outstanding chemical compatibility, and extremely low friction. In addition, PTFE lends itself to the weight constraints and pressure fluctuations involved with space travel, and has been proven over and over that it can provide mission critical levels of reliability.

Automotive

Automotive seals must withstand rugged, extreme environments that may involve everything from corrosive chemicals to extremely high temperatures. When selecting a seal material for automotive applications, properties such as low friction, wear resistance, resistance to abrasion, and durability are major concerns. 

For automotive applications, the most common choice of seal jacket material for spring energized seals include PTFE and Viton (fluoropolymer elastomer). To provide the best performance in the demanding environment of automotive seals, additives such as MoS2 (Molybdenum Disulfide) or carbon may be added to increase strength, wear resistance, and stiffness or achieve low friction.

Renewable Energy

One of the most common areas in renewable energy that requires the use of spring-energized seals is wind energy. Seals for wind turbines can be extremely challenging to design because of the wide range operating temperatures involved, problems with lubricants that can freeze in cold temperatures, extremely low friction so that energy is not wasted, and reliable performance over a long life. Seals must also exhibit low moisture absorption. 

Wind turbine seals typically use PTFE and UHMW PE, known for their low friction and self-lubricating properties. They also offer extremely low moisture absorption, a good range of operating temperatures, and good wear resistance. In addition, they have good resistance to degradation under constant UV exposure.

Oil and Gas

In the context of the oil and gas industry, LNG plants figure heavily in applications that require the use of cryogenic spring-energized seals. For such cryogenic applications, PTFE and UHMW PE have been found extremely effective. For non-cryogenic environments, Hytrel (thermoplastic polyester elastomer) is another commonly used material along with PTFE. These materials offer good performance in sub-freezing temperatures and are reliable enough to support the spring-energized seal design as it prevents leaks that could be devastating not just to humans but to the environment as well.

For other applications, issues of extremely high temperatures and pressures are involved, such as sealing solutions for wellheads. For those jobs, PEEK is often the preferred material. It possesses low friction, excellent chemical compatibility, a wide operating temperature range, and high strength. In addition, it is also one of the few polymers that can maintain its performance in sour gas environments.

Conclusion

Spring-energized seals can provide gas-tight, highly reliable sealing solutions for some of the most difficult operating environments imaginable when combined with the right material. For many sealing solutions out there, high performance polymers are a perfect complement to the ruggedness of a spring-energized seal in many different industries. If you need a spring-energized seal, regardless of industry, we can help you select the right material to provide a durable, effective seal. Contact Advanced EMC today!

by Sara McCaslin, PhD Sara McCaslin, PhD 1 Comment

PTFE Spring Energized Seals for Cryogenic Applications

When cryogenic temperatures are involved, a failed seal can have extremely serious repercussions that can include personal safety, explosions, damage to local ecosystems, and highly expensive downtime. One of the most dependable solutions to date for sealing in cryogenic environments is PTFE spring-energized seals. In this week’s blog post, we will discuss PTFE spring energized seals for cryogenic applications!

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by Jackie Johnson Jackie Johnson No Comments

Energizers used in Spring Energized Seals

PTFE spring-energized seals are one of the most popular choices for engineers in a variety of industries including oil and gas, medical, food and more. The reasons for their popularity are many, including their long service life, even wear, and their ability to perform in some of the harshest environments.  They work well in extreme temperatures; can even perform well in situations where operating conditions can vary significantly.  They usually offer a low compression set, have a long shelf life, and work very well in non-lubricated applications. One of the main reasons for these is the use of energizers, of which there are several different kinds.

As one of the key components of spring energized PTFE seals (it’s even in the name!), each of these energizers offers a different set of characteristics that allow engineers to find just the type of seal to suit their application’s needs.

In this week’s blog post, we are going to look at five different types of energizers, and where they are best used: coil springs, V springs, helical flat springs, cantilevered finger springs, and elastomeric O-rings.

Coil Spring

When people picture the spring energizing seal, the first image that comes to mind may well be the wire coil spring, also known as a spiral pitch spring.  One of its outstanding characteristics is low friction.  The angled coil spring works well where low friction and high pressure are involved, and works best in medium speed applications

V Springs

The V Spring is a cantilever, general-purpose energizing spring, which offers good performance at a relatively low cost.  The V ribbon spring (V ribbon spring energized seal) is the one to look at for the harshest, most severe applications your industry has to face.  It has been accepted as an excellent candidate for cryogenic and vacuum applications.

The v shape of this spring provides a moderate load over a wide deflection range and is used in dynamic and static applications.

Helical Spring

The helical flat spring, also known as a compression spring, is another commonly used alternative. It is typically a cylindrical shaped spring, and uses it’s coiled, mechanical form to store and release energy, which then absorbs impacts or shocks to resist compression or pulling objects.

This energizer is well adapted to a wide range of pressures, from high all the way down to vacuum conditions. It has been found especially suitable for sealing in lightweight gases or liquids. It performs the best under medium speed conditions.

Finger Spring

One outstanding performer is the cantilevered finger spring, also known as a finger spring (probably because it the shape of it reminds you of the end of your finger).

Finger spring energized seals are suited for sealing viscous media as the load is applied to the edge of the sealing lips. Seals energized by this spring also have extremely low friction, and offer low to high pressure sealing. They are best adapted to applications with speeds ranging from low to medium.

Elastomeric O-Ring

While elastomer is often synonymous with rubber, it is actually a highly modifiable polymer. Because of its affordability, ease of installation, and small space requirements, the Elastomeric O-ring is known as one of the most widely adapted sealing solutions. Known for their durability and versatility, elastomeric O-rings are suitable for dynamic or static applications with a wide range of temperature requirements.

An elastomeric O-ring energizer is especially useful when the use of metal must be avoided. It’s adapted well to extreme pressures, much like the helical flat spring.  It also works well when dead volume needs to be minimized.

In Conclusion

PTFE spring energized seals offer extreme temperature, high pressure, chemically inert static and dynamic sealing for the most demanding applications. They achieve this by using a variety of energizers, each with their own benefits depending on the application.

Whether your application is dynamic or static, low pressure or high, there is a spring energized seal for you. And Advanced EMC Technologies can help you find it!

Want to learn more about spring energized seals? Visit our product page HERE! Need sealing solutions? Contact us today.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring Energized Sealing Solutions For Cryogenic Services in LNG Plants

There are a limited number of reliable sealing solutions for cryogenic services in LNG plants, two leading polymers in use are spring-energized PTFE or UHMW seals.

Challenges of Working with LNG

Leaks involving LNG (Liquified Natural Gas) at cryogenic temperatures are dangerous to the health and safety of workers and to plant operation. Issues such as toxicity, extreme cold, asphyxiation, flammability, and explosions resulting from rapid expansion of LNG all point to the need for a reliable, leak-proof seal.

Finding an effective sealing solution for use in the cryogenic work environment of LNG plants can be extremely challenging. Keep in mind that nitrogen exists in liquid form under normal atmospheric pressure between -346°F and -320.44°F. It’s liquid to gas expansion ratio is very high at 1:694, which means as it boils (starting at its boiling point of -320.44°F) it will expand 694x its original volume. This can lead to an extremely high-pressure change if it occurs in a sealed environment, and most LNG seals must remain functional at either vacuum pressures or extremely high pressures.

Cryogenic Seals for LNG Plants

The temperatures involved with LNG happen to lie where many elastomeric and polymeric materials lose their elasticity and begin to behave as brittle materials. Some seals will also experience dimensional fluctuations related to temperature changes, further increasing the probability of failure. If temperature fluctuations are cyclical, there are going to be problems related to cyclic stress. Yet another issue related to dynamic cryogenic seals is lubrication: at such low temperatures, standard lubrication solutions simply will not work.

The Options For Sealing are Limited two either UHMW or PTFE Polymers and a Full Contact- Anti-Shrink Spring is Essential.

Both seal jacket materials can be specified PTFE, often known by its trade names Teflon or Flourolon 1000. The Ultra High Molecular Weight PE or UHMW, Fluorolon 5000 can handle the low temperatures involved in cryogenic service without becoming brittle (some grades can handle temperatures as low as -350°F) or succumb quickly to the effects of cyclical stress. In addition, both UHMW and  PTFE are self-lubricating, low friction supports dry running, and is a nonstick/slip material. In addition, both products are compatible with a wide range of chemicals, including those it would encounter in an LNG plant.

A spring-energized seal is a seal assembly that includes an energizing spring that forces the seal lip against the mating surface to achieve a highly leak-proof seal. This seal design, when combined with a PTFE lip, has been found ideal for cryogenic applications involving LNG. The spring energizer adds permanent resilience to the seal and can compensate for lip wear, eccentricity, hardware misalignment, and (perhaps most importantly when working with LNG) extreme pressures and dimensional changes. 

The recommended geometry for the spring energizer is a simple helical spring when cryogenic temperatures and either static, reciprocating, or rotary motion is involved. However, oscillatory or static motion may require the use of a solid spring. Recommended spring materials include  17-7 precipitation hardening stainless steel, 301/304 stainless steel, or, in some applications, Hastelloy, 316 stainless steel, Inconel, or Elgiloy.

Conclusion

The design of cryogenic seals for use in LNG plants can be challenging and must meet extremely high standards for reliability and safety, but PTFE spring-energized seals are an excellent starting point.