Tag Archives: eclipse engineering

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 This spec was superseded with AS8791, which eventually evolved into AMS3678.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.

How Material and Spring Type Affect Friction Calculation

Dynamic Sealing Applications

This article will discuss how we understand and control friction in dynamic sealing applications.

It’s easy to stop a leak in a system by just welding it shut. But when you create a dynamic application, you generally have a limited amount of power to move the device you’re sealing.

Friction is a force that must be overcome in all moving pieces. Controlling friction allows us to make efficient equipment that can have a long wear life and move with a limited amount of force.

There are many factors that drive friction up or down in a dynamic application. Although this blog will focus on shaft seals, the same considerations apply to piston or face seals.

Below we’ll cover the following factors and how they affect the friction calculation in our seals:

  1. Shaft material, hardness, and finish.
  2. If the system will operate when lubricated or dry.
  3. The system pressure or vacuum.
  4. System operating temperature
  5. Seal material and the types of fillers.

canted flange with hardware

Seal Substrate

As a seal supplier, we usually like shaft materials to be hardened steel with surface finishes that are highly effective. Hardness above 50 Rc usually gives long wear life.

Having a good finish of 8 Ra. will insure long seal life and carry lubrication. However, depending on the application, there are times when a super finish of 2 or 3 Ra is justified.

Depending on shaft loading, there are many choices of surface finish that can reduce friction and improve the life of the seal. Understanding the bearing load under the seal helps to understand what finish is required to withstand the operating conditions.

There are some finishes that are detrimental to seal life. An example is a heavy chrome surface that looks sturdy, but usually can’t be ground smooth and is left with large peaks or valleys. Thin, dense chrome is often the opposite, giving good seal life if applied correctly. The engineers at Eclipse Engineering are prepared to make recommendations on hardness and finish. Continue reading How Material and Spring Type Affect Friction Calculation

The Advantages of Crimped Can Seals

A combination of crimped can seals will handle a variety of applications when a rubber lip seal is not your solution.

Rotary seals are often secured in sealing hardware by crimping the sealing element in a metal can. One of the most common rotary seals is a molded rubber lip seal in a can. 

While not crimped, the can retains the sealing element, and stops the seal from rotating in the gland. Rotary sealing elements for low pressure (under 15 psi), are often nitrile or Viton rubber sealing elements.

This style of seal comes in many cross sections, and may include garter springs to help the seal stay engaged with the shaft. These seals are typically low in cost, and produced in high volume.

These seals are found in many low-pressure applications. However, as the pressures begin to climb over 10 psi and speeds run over 500 ft/min, friction generates heat, which accelerates wear on the rubber element and in turn begins to wear the mating shaft material.crimped can seal

Overcoming Friction

Friction or the resultant heat is the largest concern in rotary service.

The crimped can seal with PTFE (Teflon) elements can run with pressures in excess of 500 Psi and PV (pressure- velocity) reaching over 350,000psi-ft/ min. The crimped can allows these elements to remain secure.

The crimped case seal causes all the relative motion to remain at the sealing lip interface. With the crimped can, we have the opportunity to install multiple lips or seal cross sections to handle a variety of loads. This allows us to control leakage, and keep friction to a minimum.

We can seal most any fluid or run dry sealing gases with little or no lubrication. With widely varying temperatures, we can include springs to maintain seal contact, offset some eccentricity of shafts, keep dirt out or keep very light loads.

Continue reading The Advantages of Crimped Can Seals

Case Study: Replacing U-Cups with PTFE Spring Energized Seals in High Temperature Applications

Being commodity items, U-Cups are readily available in a number of materials and can be found on-the-shelf from multiple distributors and manufacturers in many standard sizes.

Named for the shape of their cross-section, a U-Cup’s design will be pressure energized increasing sealing effectiveness when compared to a standard O-Ring.

This means as pressure increases, the sealing lips are continually forced into the mating hardware surface, ensuring good contact at all times.

The simple and easily moldable design is an effective sealing solution to many systems in both hydraulic and pneumatic applications. Modifications in lip thickness and inclusion of an O-Ring Energizer can tailor sealing loads and wear life to specific situations.Spring Seal and U Cup

A key advantage to an elastomeric U-Cup is the relatively small and simple hardware space needed. Because of their flexible compounds, most U-Cups can be installed in a solid gland configuration.

A basic ID or OD groove is all you need for proper seal retention. Plus, no special tools or considerations need to be taken for correct installation.

U-Cups are available in many of the same compounds as standard O-Rings such as Nitrile, Fluorocarbon, and EPDM, but polyurethanes may be the most common material.

Urethane provides a good combination of elasticity/pliability and toughness. Therefore, it exhibits good sealing characteristics as well as, durability and wear resistance.

These desirable qualities make U-Cups an optimal solution for many sealing systems across multiple industries and they can be found in countless standard products. But Eclipse is approached many times a year with customers pushing the limits of standard U-Cups and in need of better solutions.

The Client’s Issue

Eclipse was approached by a leading pneumatic cylinder manufacturing seeking a sealing solution for a unique application.

While U-Cups typically provide optimal sealing performance in pneumatic cylinders, this application presented a difficult challenge.

The air cylinder was to be used as an actuator for a latch on a large industrial oven. While pressures, speeds, and cycle times were nothing out of the ordinary, the temperature at which it had to operate at was — a continuous 500°F.

Continue reading Case Study: Replacing U-Cups with PTFE Spring Energized Seals in High Temperature Applications

Rubber Energized Seals Webinar – Section 3

Cost vs. Lead Time for Rod & Piston Seals

Gallagher recently recorded the Rubber Energized Seals webinar, discussing rubber energized rod or piston seals, and the advantages and disadvantages to using some of the most common seal profiles.  This webinar is presented in conjunction with one of our trusted partners, Eclipse Engineering, Inc.  Eclipse is a designer and manufacturer of high performance engineered polymer solutions.

This section of the webinar will discuss cost vs. lead time in rod and piston seals, as well as how to choose the right seal for your application.

To view the webinar in its entirety, visit our Resources page and fill out the form, or click on the image below.Rubber Energized Seals - Webinar

Rubber Energized Seals Webinar – Section 2

Gallagher recently recorded the Rubber Energized Seals webinar, discussing rubber energized rod or piston seals, and the advantages and disadvantages to using some of the most common seal profiles.  This webinar is presented in conjunction with one of our trusted partners, Eclipse Engineering, Inc.  Eclipse is a designer and manufacturer of high performance engineered polymer solutions.

This section of the webinar will discuss some of the more common profiles for rubber energized seals, including x-rings, u-cups, buffer rings, cap seals, etc.

To view the webinar in its entirety, visit our Resources page and fill out the form, or click on the image below.Rubber Energized Seals - Webinar

Rubber Energized Seals Webinar – Section 1

Considerations When Choosing a Rubber Energized Seal

Gallagher recently recorded the Rubber Energized Seals webinar, discussing rubber energized rod or piston seals, and the advantages and disadvantages to using some of the most common seal profiles.  This webinar is presented in conjunction with one of our trusted partners, Eclipse Engineering, Inc.  Eclipse Engineering, Inc. is a designer and manufacturer of high performance engineered polymer solutions.

This first section of the webinar will discuss some of the things you should consider when designing a seal for an application, as well some of the more basic seals, such as o-rings, gaskets, etc.

Continue reading Rubber Energized Seals Webinar – Section 1