Category Archives: Eclipse Engineering

How HEPA Filters and Boundary Seals Help Protect Us During Pandemics

Boundary seals that help keep a certain environment sealed in while keeping the world out are everywhere.

If you look around your home, you may be surprised to see there are seals surrounding every door — and not just at the bottom. Your oven, microwave, and of course refrigerator door all have seals around them.

All these seals are different, yet they perform the same function. Your microwave is especially interesting, as its primary purpose is to keep microwaves from escaping the chamber that’s cooking your food. Your refrigerator seal has a magnet built into it, which keeps the door sealed shut.

Boundary seals are also found in many cell phones and electronic devices, keeping them water-resistant or water-proof (depending on the manufacturer). And in the industrial world, we have seals to create explosion-proof boxes in hazardous environments. The simple O-ring is found at the end of every cylinder cap to keep fluids in and the environment out.

We all go through great expenses to seal our houses from the outside with sturdy doors, only to find that we need fresh air here and there. Our windows have a series of seals around them keep the heat or the cold outside, but can be opened to allow fresh air when we want it.

In the same way that boundary seals work, the pandemic has many of us thinking about how to keep hazardous germs from entering into our homes. And if we have to fly, we may wonder how fresh the air is in the cabin, and if viruses have an easier time spreading inside of an airplane.

Boundary Seals in Aviation

Let’s begin with general aviation aircraft with pressurized cabins. The door’s seal is in the form of a bladder, which you pump up with the same type of bulb often found on a blood pressure cup.

Doors are especially difficult to seal, as they’re required to open and close. A rubber seal that would compress and seal the door completely would make the door too difficult to open and close.

After the door is closed, the pilot pumps up the bladder to seal the door. As the engines are wound up, the flight deck begins the process of pressurizing the aircraft. A pressure system from the engine maintains the pressure within the cabin around 8000 feet, allowing the pilot to breathe without the use of supplemental oxygen.

While these seals are not dynamic in the true sense of the word, they are constantly changing based on the altitude of the aircraft.

Most of the pressurization seals on our modern jets are static. But every door, including the luggage compartment, has seals that must be pressurized in order for the aircraft to maintain a safe level of oxygen in the cabin.

picture of HEPA filter by GoreDo Jet Planes Blow Clean Air?

Many travelers worry about getting sick on airplanes. With tight quarters and no ability to open a window and get some air, travelers may wonder whether the air from the vents above them is blowing fresh air — or if it’s circulating stale air and germs.

A few months ago, Cliff at Eclipse Seal performed a non-scientific study on a flight by asking the passengers next to him what they thought of the circulated air in modern aircraft today. Cliff was not surprised to find a wide range of answers, varying from someone envisioning a squirrel blower forcing air around the cabin, with others believing 100% of the air comes from the outside.

HEPA Filters on Airplanes

The truth lies somewhere in-between. Turns out, 50% of the air blowing through jet cabins is actually coming from the outside.

That’s one of the reasons why the air that blows through the vents is so cold — the 50% of air that comes from outside is around -30F, which is why stewardesses need to turn the heat on to keep us comfortable.

The rest of the air is recirculated air through a HEPA filter system, or “High Efficiency Particulate Air.”

This is the same air found in surgical operating theaters or clean rooms, with an efficiency that oftentimes exceeds 99% pure. In our modern-day aircraft, this filter helps stop the spread of whatever just came out of that guy’s mouth 5 rows up, cleans cigarette smoke, and even works to stop the spread of infectious viruses through the cabin.

If you’re traveling on one of the silver birds, your best option for the cleanest air is to turn that overhead jet on high and let it blow around your face. This funnel forces air that may be lingering around your nose and mouth aside, providing a fresh stream of cool, clean air.

Cliff even spoke to the pilot or driver of an A320, who has seen the process of cleaning the HEPA Filters. He claimed it was about as nasty as cleaning…well…you get the point.

Another pilot friend of Cliff’s even suggested that if you have to travel during the coronavirus outbreak, you should turn the air on and allow the HEPA filters the opportunity to blow clean, fresh air over your nasal cavities, promoting a safer ride and reducing the probability of infection.

So, bundle up, turn on the jets, and sit back and enjoy the ride. The door seals will keep you breathing, and the HEPA filters could keep you safe.


The original article was written by Cliff Golstein, CEO at Eclipse Seal and can be found on their website.

Gallagher Fluid Seals is an authorized distributor of Eclipse Seal. For more information about how Gallagher and Eclipse can help for your custom application, contact Gallagher.

The Advantages and Disadvantages of the Channel Seal

The Channel Seal (or Cap Seal, as it’s often referred to), was one of the earliest forms of Polymer or Teflon sealing in the seal industry.

The product is easily applied. It didn’t replace the O-ring, but instead offered improved life while reducing drag.

In doing so, hydraulic and pneumatic systems operated cooler and quieter, while improving overall performance of the product.

picture of channel seal

Evolution of the Channel Seal

Before the Channel Seal, the Backup ring was established. The first Backup rings started out as leather, as this material was readily available and could be easily formed into any shape with simple dies to stamp the Backup ring out.

Back up rings provided support for the O-ring, allowing the O-ring to operate at higher pressures, while closing off the Extrusion or “E” gap. This stopped the O-ring from being nibbled in the extrusion gap, therefore extending the life of the O-ring.

Teflon Backup rings were a big improvement, as they would better fill the gap and would stay put (as opposed to leather, which tended to shift in the groove). With the use of two Backup rings, an O-ring was well supported from pressure in both directions.

It was a simple matter to connect the two Backup rings with a thin membrane of Teflon, which removed the O-ring from the sealing surface. This change reduced drag and improved performance, while still maintaining an excellent mechanism for extrusion resistance.

This design was relatively simple to machine out of Teflon, but installation was a challenge, as the Backup rings were full depth. This caused the seal to become distorted during the install process. Today, we almost never see this type of design.

With CNC machining, the ability to nestle, and an O-ring design in a complex Teflon shape, it gave rise to what is referred to today as the Channel Seal, or Cap Seal.

This style seal offers an abundance of advantages over standard back-up rings and the early version of the Channel Seal, which was simply a Backup ring with the membrane of Teflon in-between. Continue reading The Advantages and Disadvantages of the Channel Seal

The Manufacturing Challenges of Tiny Spring Energized Seals

tiny spring energized sealEclipse Engineering has in-house capabilities to manufacture seals up to 55 inches in diameter, and over 100 inches through production partners.

While seals with huge diameters certainly grant their own significant levels of intricacy, here we’ll look at the other end of the spectrum: the micro-sized seals.

We won’t just look at a simple seal ring, but an inherently more complicated and geometrically detailed spring energized seal. As we’ll see, very small diameters make multiple manufacturing aspects more involved and challenging.

The Client’s Issue

A sealing solution in a customer’s epoxy dispensing equipment. They needed an effective seal for the reciprocating rod responsible for the flow-control and metering of the epoxy while being dispensed.

Operating Conditions:

  • Reciprocating Rod Seal
  • Epoxy Dispensing Head
  • Rod Diameter: 1.2mm [0.047”]
  • Stroke Length: 6mm [0.236”]
  • Cycle Rate: 15 per min
  • Media: Epoxy
  • Operating Pressure: 1,500 PSI
  • Temperature: 70° to 150°F

In general terms, most viscous media sealing solutions have three things in common:

  1. A variant of UHMW for the seal jacket,
  2. heavy spring loading, and
  3. multiple point contacts with increased interference.

In most cases, multiple nested V-Springs are incorporated to provide optimal load and energize the compound contact points on the seal. With this formula, we’ve had great success sealing media like epoxy, urethane, silicones and acrylics.

The heavy loading is necessary to effectively wipe the reciprocating rod. This is balanced with the correct material and design geometry to provide long wear life of the seal, which has the potential to be compromised under such loading.

The challenge in this case was to incorporate these same proven principles in a micro-sized seal.

The Eclipse Solution

Continue reading The Manufacturing Challenges of Tiny Spring Energized Seals

The History and Ingenuity of the Buffer Ring: Part 1

Back in the mid 70’s, an engineer named Roy Edlund of Busak & Luyken designed a high-pressure seal that had an uncommon effect of rocking in the groove. This action occurred when pressure was created on the retract side of a cylinder as the rod was being retracted into the cylinder.

The material used for the seal was generally a bronze-filled Teflon, which could resist extrusion and have a long seal life. Because the seal ring was made from a grade of filled Teflon, a small amount of oil would leak under the lip as the cylinder was being extended.

One of the most unique features of this style seal was that as the rod was being retracted back into the cylinder, the buffer ring would rock or rotate slightly to the low pressure side thereby forcing leaked oil back into the retract side of the cylinder under the buffer ring.

This seal is commonly called a Buffer Ring (for reasons we’ll explore in this blog), but this seal helped usher Teflon into most high-pressure hydraulic systems today.

picture of buffer ring

Pre-Buffer Ring Sealing Problems

Manufactures of high-pressure hydraulic systems in equipment, such as back hoes or hydraulic cranes found that their products were having seal failures prior to reaching warranty. This resulted in downtime and large warranty expense to repair these cylinders in the field.

In normal operations, the standard U-Cup made from a variety of Urethanes did an excellent job of creating a “near” zero leak sealing system. The problems would occur as the “bulk” oil temperature rose due to usage, pressure spikes in the system would cause premature failure of the Urethane U-Cup.

It was the pressure spikes that usually wreaked havoc with the U-cup seal design, causing the urethane to break down and eventually crack, creating a leak, and resulting in equipment shut-downs.

The Buffer Ring Solution

The Buffer Ring turned out to be the answer. By adding another sealing element in front of the Urethane U-cup, the life of the U-cup was greatly extended, overall friction in the system was reduced, and the bulk temperature in the hydraulic system was lowered.

All these advantages came by adding a sealing element. The true savings showed up in dramatically improving equipment up time. This also reduced warranty costs of equipment to the OEM.

How Does the Buffer Ring Work?

The answer to this question was initially difficult for many manufacturers to understand. Normally, putting one seal in front of another should cause a pressure trap, sending pressure loads much higher than relief valve settings, which locks up the cylinder.

The secret was in the way the Buffer Ring performed its job.

The seal leaking is very important to its design. If oil didn’t reach the U-Cup, the U-cup would generate heat and begin to wear out prematurely. So, since the Buffer Ring allowed a small amount of fluid to seep under the lip, this fluid lubricated the U-cup and kept its friction to a minimum.

Being elastomeric in nature, the U-cup did an excellent job of wiping the rod nearly completely dry.

But what about the pressure trap?

picture of buffer ring in application

The Buffer Ring and its unique quality allowed fluid back into the system. Testing verified that this would happen anywhere from zero to about 100 PSI.

The U-cup spent most of its life in a well-lubricated, low-pressure / low-temperature environment compared to the original design.

The Buffer Ring also made suppliers of U-Cups extremely happy, as their failed seal had been given new life compared to the holes blown through the back of their urethane product. Continue reading The History and Ingenuity of the Buffer Ring: Part 1

Spring Types and Materials in Sealing Systems

Springs are an integral part of all sealing systems. A simple air cylinder has O-rings to seal in the air, and the O-ring exhibits spring-like qualities to ensure a good seal over a broad temperature range.

But what are the different types of springs and materials in sealing systems? And how do you choose the best for your application?

image of metal spring types

Metal Springs

Metal springs, such as the Cantilever and Canted Coil spring, are used to energize polymers such as Teflon and ultra high molecular weight polyethylene (UHMW) to allow sealing in a wide range of temperatures. Selecting the correct spring material is critical to the life of the seal.

Metal energized seals are often subjected to a wide variety of fluids and temperature ranges, which then requires the correct material choice for the life of the seal in the application.

One of the earliest metal springs was the flat band or marcel expander, often made from common materials like 300 series Stainless Steel or heat treated 17-7 Stainless Steel.

These materials are often chosen for their tensile strength. But due to the cost to manufacture and the high volumes of spring required, these two expanders were often relegated to industrial or aerospace hydraulic systems.

If system fluids were not compatible with Stainless Steel, customers generally went to a different sealing system to avoid the high cost of short runs in these styles of energizers.

O-Rings cover a wide range of temperatures, and fluids, but generally not both. If there are multiple fluids involved, O-Rings often fail to provide compatibility over a range of fluids.

The use of Cantilever, Canted Coil or Helical coiled spring allowed for long runs and lower costs. The most common spring material is Stainless Steel, but these styles of spring lend themselves to materials that have a wide range of chemical and temperature range while maintaining tensile strength.

Alternative Spring Materials

Some of the more common alternative materials are Hastelloy and Elgiloy. While 17-7 is available, it’s seldom used because Elgiloy (while more expensive per pound) is often run at a higher volume, bringing the overall cost down making 17-7 less attractive due to cost.

Another style metal spring for polymers is the Garter spring. Garter springs are normally run on a per job basis, but because it’s made from wire, it can easily be wound from any material like Elgiloy or Stainless.

Garter springs are often used in rubber style lip seals, but we often find them coupled with polymer-style seals.

Mechanical Seals

Mechanical face seals typically marry a material with the fluids the seal will be running in. Mechanical seals have the overall body and internal springs made from specific materials capable of handling variations in temperature and fluids.

PEEK in Seals

Polymers are thought of as seal materials, but PEEK has been used as a spring in polymer-style seals. PEEK can be wound into helical style springs, and also formed into cantilever springs. As a Helical style, it can be wound into a diameter to energize Teflon or rubber lip seals.

If you consider radiation service, a PEEK spring makes an excellent choice keeping metals out of the seal.

How to Choose the Right Spring Material

While there are a variety of metals, often economics determine the practicality of specialty metals.

A consideration is reviewing the hardware used in the application as to what spring material is acceptable in an application. We often review what the customer is using in the rest of the service for determining a spring material.

Temperature is often a key factor in determining materials for spring. Elgiloy tends to do an excellent job in maintaining tensile strength at elevated temperatures.


The original article can be found on Eclipse Engineering’s website and was written by Cliff Goldstein.

Gallagher Fluid Seals is an authorized distributor of Eclipse engineering. For more information about choosing the right spring material for your application, contact our engineering department today.

The Many Uses of Polytetrafluoroethylene Seals (Teflon)

Better known as Teflon in the industry, Polytetrafluoroethylene is widely used in practically every industry on and off the planet (and even beneath its surface!)

Medical Uses

white ptfe o-ring-teflonThis material’s primary claim to fame is its resistance to most chemicals. It inherently has an extremely low coefficient of friction, it’s easily machined from rods, tubes, or compression-molded shapes.

It’s one of the few polymers that are approved for medical implants due to its inertness to bodily fluids — the immune system principally ignores its presence in the body.

Moving away from the body, you’ll find PTFE or Teflon products in medical devices such as heart lung machines, rotary tools for cutting, and sealing devices for maintaining fluid streams for irrigation and pumping. Tiny fragments that may come loose during usage are not harmful to the body, and simply pass through the system.

Pharmaceutical Uses

In the pharmaceutical industry, Teflon is used in the processing of drugs for equipment used to manufacture such as mixers, presses, and bushings. Teflon is found in a variety of applications, as any debris from the seal will pass through the body without consequence.

When considering press machinery (which are often water driven to ensure any leakage will not spoil the product), Teflon seals are often used to help reduce friction — especially in repetitive presses where a build-up of heat would be detrimental to the seal and the product.

Food & Beverage Uses

Mixers are another area to ensure keeping grease and other contaminants from the motor to not descend into the product from the mixer shaft.

Another area is pressure vessels where two shells are clamped together to ensure product remains sealed inside. Failure of these seals usually results in loss of product.

Non-metal bearings that don’t requiring grease in rotary motion are an excellent place for Teflon style bushings. These bushings provide long life with very low friction while not contaminating the product. Shaft wear from the bushing may be eliminated with the use of Teflon.

Types of PTFE (Teflon) Seals

Seals in the medical field can be as simple as a static O-Ring, or a mechanical face seal which is costly and requires special consideration during installation. Most dynamic applications can be resolved with spring-energized style seals, which often have very low friction and can be clean in place (CIP) if required.

There are different styles of springs, such as cantilever or canted coil that provide varying loads. The cantilever-style spring-energized seal provides a linear load based on deflection providing a high level of seal-ability. It can be silicone-filled to provide CIP for ease of washing, and there are a variety of materials that are FDA compliant and that work well in both viscous and pure aqueous fluids.

Canted coil spring-energized seals provide a unique feature of controlling the load the spring exhibits on the sealing element. This allows for control of a device being manipulated during a procedure.

The polymer properties give the user materials with the lowest possible friction, while still sealing in an application. The load from a canted coil spring allows the user to feel a tool in a catheter while passing the catheter through a tube, and still retaining a seal.

As you can see, PTFE has a variety of uses across a broad range of industries. GFS’ partner, Eclipse Engineering, manufactures PTFE and can help provide solutions to customers facing both simple fixes or complex problems.

Contact us today to see if PTFE might be the right choice for your application.


For custom engineered parts, or for more information about a variety of PTFE seals we can provide, contact Gallagher Fluid Seals today.

The original article was written by Eclipse Engineering and can be found on their website.

Angled Spring Grooves for Custom Spring Energized Ball Seats

A ball valve is a simple and robust valve used in applications and industries across the spectrum. It consists of a ball with a hole through the center that can be rotated 90°.

custom spring energized ball seat

The hole is either aligned with flow and open, or perpendicular to flow and closed. The straightforward, quarter-turn action is fast and simple to operate, and the position of the handle provides a clear indicator of whether the valve is open or closed.

Most ball valves are typically used as a shut-off valve. Many households likely use ball valves at some point in the water supply plumbing.

Not relegated to common plumbing, many industries use ball valves for critical control applications including aerospace and cryogenics. Their reliable operation and high-pressure handling ability make them an attractive solution for many specialty operations.

Seals Inside a Ball Valve

The seals inside the ball valve play an important role in their performance and reliability. There are two main seals in a common ball valve, which are referred to as seats.

The seats are typically machined or molded to match the diameter of the ball and are mechanically compressed against the ball face. Seat material varies by application needs, but virgin PTFE is frequently used for this application.

The Client’s Issue

The customer wanted a very specialized ball seat: utilizing a spring energizer in the seat. While easy to suggest, this would create a significant challenge in how the seal is manufactured.

The customer was looking for a sealing solution for a ball valve in their industrial gas processing plant. The ball valve would serve as a critical shut-off point in the system. The valve would be actuated by an electric motor, and could therefore be operated remotely.

The customer was looking for an improvement in the overall wear life of the ball seats, while still providing consistent and predictable actuation torque. Being motor activated, the torque required to move the ball open or closed was limited—so the friction generated by the ball seats would need to be carefully controlled.

Operating Conditions:

  • Ball Valve Seat
  • Ball Diameter: Ø2.500”
  • Media: Petroleum Processing Gases
  • Pressure: 100 PSI
  • Temperature: -40° to 175°F

The Challenge

Continue reading Angled Spring Grooves for Custom Spring Energized Ball Seats

5 Polymer Bearing Configurations and Their Advantages

Polymer BearingPolymer wear rings were developed to offer an alternative to dissimilar metal wear rings.

One of the advantages to using a polymer material such as nylon or filled-Teflon instead of a metallic bearing . Whereas when you use bronze or metallic bushings, these materials are prone to point loading on the edges of the bearing.

This property of polymer bearings combined with solid lubricants can yield a product that is much less likely to damage moving components.


5 Advantages to Polymer Wear Rings

  1. Polymer style bearings can be held to very close tolerances in the radial dimension to provide support without excessively opening the extrusion (E) gap by a large amount. Polymer bearings such as filled Teflon can support a compressive load up to 1000 PSI. Nylons up to 36,000 PSI and polyester fiber with resin, up to 50,000 PSI.
  2. Hydraulic cylinders that are found in excavators often use higher compression materials because they experience extreme side and shock loads. However, most applications do very well with filled Teflon materials.
  3. Bearings come solid or split. If designed properly, split bearings provide equivalent support, while improving installation options with no compromise in performance. Solid bearings, or bushings, are convenient when installing on the outboard side of a rod groove. Split bearings are essential when installing in a piston groove designed to function internally in a system.
  4. Nylon or composite bearings are typically cut to allow for installation due to their stiffness. However, a Teflon bushing can be made into a ring, or cut from a roll of sliced strip.
  5. The only time a bushing needs to be cut from a ring is if installation does not allow the strip to be deformed for a clean install. Strip installation allows for variability in length, lower manufacturing costs, and the product can generally be acquired off the shelf.

Materials for Polymer Bearing Configurations

When selecting materials, we must consider the maximum load, the speed of the system, and whether there is any lubrication in the system.

The load (or pressure over area) that the bearing will see is the first consideration. This dictates which materials will be the best fit.

It’s important to use a material that has a minimum compressive strength rating so that it will not fail under the highest loading condition. The industry standard is to employ a safety factor so that the bearing is specified to be used well beyond its design limit.

Teflon should be your first consideration due to cost and ease of installation. Nylon or composites will provide much higher load rating, but the cost and installation need to be considered.

Teflon and composites provide service without lubrication, and the composites provide excellent service in aqueous solutions. Bushings are typically used in medium to slow reciprocating service. Rotary creates challenges that may or may not work depending on the design of the bushing.

There are many series of injection molded nylon bushings. However, nylon in low-lubrication or high-loading may create high-friction, and can be noisy. Nylon, as a low-cost bushing, can be used in some high load situations.

A final consideration before going into large scale production is the cost of taking a bearing design into high production. Some bearing materials are expensive and can only be processed by machining, which limits the cost reduction scenarios at high volumes.

Eclipse Seal

Materials such as filled-PTFE or thermoplastics that can be molded offer cost competitive solutions for high-production applications. Eclipse provides bearings in everything from low-quantity applications, such as bridges and dams, to mid-quantity applications in aerospace.


Gallagher Fluid Seals is a preferred distributor of Eclipse Engineering. Call us at 1-800-822-4063 for more information on Eclipse seals.

Article written by Cliff at Eclipse Engineering, Inc. For the original article, visit their website.

How AMS3678 Ensures Consistency in Sealing Materials

When it comes to designing and developing seals, the aerospace and industrial industries need a basis to allow production anywhere in the world.

One of the first PTFE (Teflon) standards, AMS3678, describes Teflon and the addition of fillers. This was used in conjunction with Mil-R-8791, which is one of the Mil specs describing a backup ring device.

The origin of all these specs dates back to the creation of the O-ring.

AMS3678The Origin of the O-Ring Patent

In 1939, Niels A. Christensen was granted a U.S. Patent for “new and useful improvements in packings and the like for power cylinders.” These referred to improved packing rings made of “solid rubber or rubber composition very dense and yet possessive of great liveliness and compressibility.” These products were suitable for use as packings for fluid medium pistons (liquid or air). The improved packing ring is the modern O-ring.

There was a progression of standards for the O-rings created by individual countries, such as AS568, BS 1806, DIN 3771, JIS B2401, NF T47-501, and SMS 1586. Eventually, AS568 became more accepted in the industry.

The backup ring was originally created to help improve the O-ring’s ability to resist extrusion. Teflon was widely used as one of the materials for backup ring devices. Standards were created to unify the production of this Teflon device.

The Progression of Mil Specs

The progression of standard changes has led to AMS3678/1 for Virgin PTFE through AMS3678/16. These standards describe a group of Virgin- and filled-PTFE materials accepted by the industry for manufacturing seals and back-up ring devices.

Mil-R-8791 was canceled in February 1982. This spec was superseded with AS8791, which eventually evolved into AMS3678.

AMS3678 is a tool used by customers and Teflon suppliers to create uniformity in the manufacturing and processing of seal and bearing materials. The standard is inclusive of most of the compounds upon which the industry was built.

When customers approach with an old “mil spec”, they are pushed to the new AMS spec which is currently active. Eclipse manufactures to the spec so their customers will have the confidence that they manufacture to a known standard.

When crossing custom materials from well-known sources, customers are driven to an accepted spec that is equivalent to the original source of the material. This helps customers sell their products with internationally-known materials rather than custom, home-grown compounds that are often intended to single source those materials.

There are several qualifications of the spec that suppliers must observe. This includes dimensional stability tests. This test ensures the material has been properly annealed, and that the seal or backup ring will fit and function as it was originally intended.

Eclipse is uniquely qualified to supply parts to the latest AMS3678 specification. They understand the scope of the specification which allows us to ship parts with fully traceable certification.

AMS3678 helps validate a material to a customer to ensure they get the same material processed the same way with each order. Beyond this, there are other ways to determine what makes a part process-capable.

Continue reading How AMS3678 Ensures Consistency in Sealing Materials

Case Study: Balancing Extrusion Gap and Wear Ring Exposure in a High-Pressure C02 Extraction Application

Seal designers often feel caught in the constant struggle to balance the demands of a sealing application with physical and material constraints.

picture of piston

At Eclipse, it’s an engineer’s job to understand and weigh these limitations with the goals of the application. For example, when a customer needs an extremely low friction seal that also has very high sealability, there’s always a compromise that needs to happen.

A magical seal material that has the pliability and excellent seal characteristics of rubber, and the low-friction, high-wear resistance and temperature range of PTFE simply doesn’t exist.

Another frequent scenario is a customer needing a seal to accommodate loose or poor hardware tolerances, yet has a very small physical envelope to incorporate a seal. The smaller the seal, the smaller the effective deflection range due to the physical limits or an O-Ring or spring.

While the application might need to cover the range of a 400-series spring or O-Ring, there may only be room for a seal the size of a zero series, which presents a problem. Similarly, a customer might have the desire for a seal with very long wear life, yet the hardware assembly may be severely limited in the area meant for the seal.

There have been several times where Eclipse has been approached with applications where a space for a seal was never considered in the original design. Without a properly sized seal, wear life has the potential to be restricted due to the fact there is less seal material available to be worn away before the structural integrity and sealability is compromised.

Another common problem in sealing applications where bearings are needed is the balance between having enough exposure for the wear rings and not creating too large of an extrusion gap, which can lead to complications for the seal. Eclipse was approached by a customer facing this issue in their high-pressure, supercritical CO2 extraction equipment.

The Client’s Issue

With the growing popularity of cannabis-derived products such as CBD oil, extraction processes are being examined for increased productivity and durability.

A customer was looking to redesign the piston seals used in their CO2 SFE extraction equipment. The ideal seal would have improved wear life and longevity as well as improved lead-time and availability of the seals once they needed to be replaced.

The customer’s increased production volumes and run-rates where quickly wearing out the OEM seals, and they were unhappy with the lead-time and service of the original seal supplier.

With some of the best lead-times in the industry for custom PTFE seals, Eclipse knew it could deliver if an improved seal design could be implemented.

Operating Conditions:

  • Reciprocating Piston Seal
  • Bore Diameter: Ø3.250”
  • Stroke: 6”
  • Cycle Rate: 35 cycles per minute
  • Media: CO2
  • Pressure: 800–5,000 PSI
  • Temperature: 65° to 175°F

The customer was willing to redesign the piston seal gland configuration, but the overall length of the piston couldn’t be changed to ensure correct functionality in the original equipment.

Since there was significant side-loading of the piston, wear rings would be necessary for both proper piston guidance and to safeguard against any potential metal-to-metal contact between the piston and bore.

If metal-to-metal contact occurred and the bore was scratched or galled, the customer would face extensive down-time while they waited for a replacement part. This would cost them a significant amount of money from lost productivity, not to mention the cost of the replacement bore.

To mitigate this potential risk, the customer didn’t want to eliminate wear rings or reduce their width. Eclipse needed to find a solution that worked with this specific design constraint, and with the amount of axial space available on the piston for the seal.

This space constraint presented a challenge. With the importance of proper wear ring exposure in the system, the extrusion gap needed to be sizable. And with limited space to either substantially extend the heel of the seal or incorporate a back-up ring, Eclipse needed to utilize special design techniques and features to present a high wear life seal.

The Eclipse Solution

Balancing extrusion gap and wear ring exposure is a very typical problem in the seal industry. In systems where operating pressures are relatively low, this might not be a problem. But when pressures increase, seal integrity can quickly become compromised.

In a piston application, wear-ring exposure and seal extrusion gap become the same entity. In most cases, once tolerance stack-ups are performed with both the bearing and hardware dimensions, the resulting necessary exposure dimension will be far beyond the typical maximum extrusion gap recommendation for the seal.

If not given enough exposure on the piston, the wear ring has the potential to be loose in the groove, making it ineffective as a bearing. This would place undue side loading on the seal, leading to premature failure and/or the piston contacting the bore.

In almost every case, this metal-to-metal contact will likely gall or score the bore enough to destroy a proper sealing surface finish, if not more extensive damage.

On the other hand, if the extrusion gap that results from the need for bearing exposure is too large, the seal will eventually be pushed into the gap by the pressure and ultimately cause a failure. The higher the pressure of a system, the smaller a recommended extrusion gap will be.

Without any other considerations, extrusion gaps are typically suggested to be made as small as possible. This fact is obviously diametrically opposed to the need for bearing exposure.

To combat large extrusion gaps, spring energized seals can be made with an extended heel design. This physically puts more sealing material behind the seal, which can be deformed into the gap without affecting the critical area of the seal.

The other common solution is to incorporate a back-up ring behind the seal. A back-up ring can be designed to reduce the size of the extrusion gap that the seal is exposed to.

Both of these solutions require additional axial space on the piston, which Eclipse didn’t have the luxury of working with.

The first step: using a smaller spring series than the hardware cross-section would typically call for. The smaller spring would effectively allow the heel of the seal to be extended, aiding in the extrusion resistance of the seal. This also means the sealing lips would be thicker than normal.

Eclipse utilized this extra material in the lips to modify the seal geometry to further fortify against high pressure failure. The ultimate failure mode of a spring energized seal due to extrusion is usually when deformation of seal reaches the hinge point of the spring cavity. To guard against this, Eclipse offset the location of the spring groove to thicken this vulnerable hinge point.

Eclipse chose its ET040: Polyimide/MoS2 filled PTFE for the spring energized seal jacket. While this isn’t the most extrusion resistant material Eclipse has to offer, the customer’s stainless-steel bore material was limiting on how aggressive the seal material could be.

ET040 would provide a good level of toughness without wearing the bore. The added internal lubricity reduces friction, and the fine particle size of the Polyimide improves sealabilty while sealing gases such as CO2.

Eclipse chose its ET010: bronze-filled PTFE for the wear rings. This industry standard bearing material fit well within the design objectives of the project.

How the ET040 and ET010 Performed

With Eclipse’s revised seal and piston design, the customer saw increases in seal life and reliability. This allowed them to run their production processes for longer intervals between scheduled maintenance.

The reduced downtime increased plant productivity, positively affected the customer’s bottom-line, and allowed them stay on top of shipments of their high demand product.

The customer was also very pleased with Eclipse’s comparatively short lead-time and reliable delivery on replacement seals. Their moderate investment in redesigning their piston configuration to use Eclipse seals proved to be a profitable choice.

eclipse engineering seal and wear rings


Article written by Eclipse Engineering, Inc. For the original article, visit their website.

Gallagher Fluid Seals is a preferred distributor of Eclipse Engineering. Call us at 1-800-822-4063 for more information on Eclipse seals.