Energizers for Spring Energized Seals
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.