Tag Archives: O-Rings

How Much Do You Know About Compressive Stress Relaxation? CSR Part 1

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s Website and was written by Dan Ewing, senior chemical engineer, Parker Hannifin O-Ring & Engineered Seals Division.


black o-ringsCompressive Stress Relaxation (CSR) is a means of estimating the service life of a rubber seal over an extended period of time. As such, it can be thought of as the big brother of compression set testing. Rather than measuring the permanent loss of thickness of a compressed rubber specimen as is done in the compression set, CSR testing directly measures the load force generated by a compressed specimen and how it drops over time. In part 1 of our blog series, we will explore the theory of CSR testing, common test methods, and how CSR differs from compression set testing.

Theory of Compressive Stress Relaxation Testing

To understand the value of CSR testing and how it differs from compression set testing, it is helpful to return to the basic theory of how a rubber seal functions. In a standard compressed seal design, a rubber seal is deformed between two parallel surfaces to roughly 75% of its original thickness. Because the material is elastic in nature, the seal pushes back against the mating surfaces, and this contact force prevents fluid flow past the seal, thus achieving a leak-free joint. Over time, the material will slowly (or perhaps not so slowly) relax. The amount of force with which the seal pushes against the mating surfaces will drop, and the seal will become permanently deformed into the compressed shape. In compression set testing, the residual thickness of the specimen is measured, and it is assumed that this residual thickness is valid proxy for the amount of residual load force generated by the compressed seal. In CSR testing, the residual load force is measured directly.

In practice, compressive stress relaxation results are typically presented very differently from compression set results. In CSR testing, it is common to see multiple time intervals over a long period of time (3,000 hours or more of testing), thus allowing a curve to be created (see Figure 1). In practice, however, specifications are written such that only the final data point has pass/fail limits. In compression set testing, it is common to see a single data point requirement with a single pass/fail limit. Multiple compression set tests can be performed to create a curve, but this is almost always done for research purposes rather than for specification requirements. In most cases, compounds that excel in compression set resistance also demonstrate good retention of compressive load force over time. However, there are exceptions.

Figure 1: Typical CSR curve. These results display a fluorocarbon seal material immersed in engine oil at 150°C.

Continue reading How Much Do You Know About Compressive Stress Relaxation? CSR Part 1

How to Properly Choose Commercially Available O-Ring Cross Sections

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s website and was written by Dorothy Kern, applications engineering lead, Parker O-Ring & Engineered Seals Division.


There are 400+ standard O-ring sizes, so which is the right one for an application? Or maybe you are wondering if one O-ring thickness is better than another. This short article will walk through some of the design considerations for selecting a standard, commercially available O-ring for an application.

Design Considerations

Hardware geometry and limitations are the first consideration. A traditional O-ring groove shape is rectangular and wider than deep. This allows space for the seal to be compressed, about 25% (for static sealing), and still have some excess room for the seal to expand slightly from thermal expansion or swell from the fluid.  Reference Figure 1 as an example. Once the available real estate on the hardware is established, then we look at options for the O-ring inner diameter and cross-section.

AS568 Sizes

From a sourcing perspective, selecting a commercially available O-ring size is the easiest option.  AS568 sizes are the most common options available both through Parker and from catalog websites.  A list of those sizes is found in a couple of Parker resources including the O-Ring Handbook and the O-Ring Material Offering Guide. They are also listed here.  The sizes are sorted into five groups of differing cross-sectional thicknesses, as thin as 0.070” and as thick as 0.275”, shown in Table 1 below.
Continue reading How to Properly Choose Commercially Available O-Ring Cross Sections

Reduce Downtime and Costly Seal Replacements: Seal Failure Diagnosis Part 2

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s Website and was written by William Pomeroy, applications engineer, Parker O-Ring & Engineered Seals Division.


As mentioned in part one of Parker’s seal failure blog series, O-ring and seal failures are often due to a combination of failure modes, making root cause difficult to uncover. It’s important to gather hardware information, how the seal is installed, application conditions, and how long a seal was in service before starting the failure analysis process. In part 1, compression set, extrusion and nibbling, and spiral failure were discussed. In part 2 of Parker’s series, they will review four other common failure modes to familiarize yourself with before diagnosing a potential seal failure in your application.

Rapid gas decompressionRapid Gas Decompression

Rapid gas decompression (commonly called RGD, or sometimes explosive decompression (ED)) is a failure mode that is the result of gas that has permeated into a seal that quickly exits the seal cross section, causing damage.

Detection of this failure mode can be difficult, as the damage does not always show on the exterior.  When the damage is visible, it can look like air bubbles on out the outside, or perhaps a fissure that has propagated to the surface.  The damage may also be hidden under the surface.  If the seal is cut for a cross section inspection, RGD damage will look like fissures in the seal that may or may not propagate all the way to the surface.

Parker’s guidance as to how to avoid this failure mode is: 1) Keep the depressurization rate lower than 200 psi per minute.  If this cannot be achieved, they would suggest 2) RGD resistant materials.  Parker offers these RGD resistant options from the HNBR, FKM, EPDM, and FFKM polymer families.

AbrasionAbrasion

Abrasion damage is the result of the seal rubbing against a bore or shaft, resulting in a reduction of cross sectional thickness due to wear.  As the seal wears, it has the potential to lose compression on the mating surface.  This wear is compounded by the fact that dynamic applications already have lower compression recommendations.

To reduce risk for this failure mode, it requires consideration during design and seal selection.  The surface finish and concentricity of the hardware will be very important considerations.  A smooth surface results in less friction (suggest 8 to 16 RMS), which in turn results in less wear.  Increasing the durometer of the seal material helps resist wear, and there are also internally lubricated materials that could be employed.  If the application is high temperature, one should consider the impacts of thermal expansion on the elastomer being used.  The thermal expansion increases contact pressure, which would increase friction / wear. Continue reading Reduce Downtime and Costly Seal Replacements: Seal Failure Diagnosis Part 2

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

Semiconductor Fabs Lower Cost of Ownership with HiFluor Materials

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s Website and was written by Nathaniel Reis, Applications Engineer for Parker O-Ring & Engineered Seals Division.


parker hifluor processIn our semiconductor entry from last month, we noted that lowering the cost of ownership is a multi-faceted goal. We discussed how one of the areas for potential improvement is mechanical design and how the Parker EZ-Lok seal is a major solution to mechanical seal failure. In this entry, we’ll investigate a notably different type of cost-reduction opportunity – material selection – and see how Parker’s innovative HiFluor compounds can reduce seal costs to as little as half.

Critical Environments

When it comes to the seal industry, the semiconductor market is well known as one where the most premium, chemical-resistant compounds are a necessity. Microelectronic manufacturing processes involve chemistries that push the limits of what elastomeric compounds can withstand in terms of both chemical aggressiveness and variety. The perfluorinated materials (FFKM) capable of withstanding these environments require intricate manufacturing processes regulated by closely-guarded trade secrets and the significant investment of resources.

These factors drive the price of FFKM compounds to the point of being as much as 50 times the cost of any other variety. Cutting just a slice out of this cost can result in significant savings – a chance to take out a quarter or even half the pie would be advantageous to the overall bottom line. Fabricators should be continually on the lookout for more cost-effective compounds that show equal performance in their pertinent operations.

hifluor compound pictureThis is why Parker’s HiFluor compounds offer an opportunity for cost savings that shouldn’t go unnoticed. A unique hybrid of performance between FFKM and the simpler technology of fluorocarbon (FKM) elastomers, HiFluor offers the most superb chemical compatibility in the many semiconductor environments where the high temperature ratings of FFKM aren’t necessary – and at a fraction of the cost.

Not only can HiFluor be used where even FKM is lacking, but its performance in applications with aggressive plasma exposure is spectacular as well. This can be observed by its overall resistance to plasma-induced material degradation. However, Parker has also developed multiple formulations that display extremely low particle generation when most materials would be expected to suffer severe physical and chemical etch.

Solutions and Cost Savings

As an example: One major semiconductor fab had several factors (other than their seals) dictating the frequency of their preventative maintenance (PM) intervals. The fab wanted to replace their seals at these intervals as a precautionary measure to limit the chance of them becoming another PM-increasing factor. However, this caused these premium FFKM seals to be a source of inflated cost. Parker assisted with a process evaluation that resulted in over half the seals being replaced with cost-effective HiFluor O-rings, while the tool regions with more intense plasma exposure were reserved for the elite performance of Parker’s FF302.

Another major fab in the microelectronics industry switched from FKM to FFKM seals in their oxide etch process. The tool owner achieved the desired performance improvement, but soon began searching for less expensive options. The owner recognized the plasma resistance and low particulate generation of Parker’s HiFluor compound, HF355. After implementing this change, he retained the performance improvement, but at a fraction of the cost.

Semiconductor tool owners understand that their aggressive processes require the most robust, expensive FFKM seal materials. The price tag on these seals is greater than those from any other compound family. Fortunately, HiFluor is a proven sealing solution that can bridge the gap and provide the same kind of high performance at a much lower cost.


For more information about Parker O-Rings, including HiFluor, or to find a custom solutions for your application, contact Gallagher Fluid Seals today.

Semiconductor Fab Processes Benefit From Retention Ribbed EZ-Lok Seals

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s Website and was written by Nathaniel Reis, applications engineer, Parker O-Ring & Engineered Seals Division.


When it comes to semiconductor fabrication processes, reducing the cost of ownership is a multi-faceted goal approached from a variety of angles. Tool engineers and equipment technicians take pride in their ability to identify factors that limit tool uptime. One constant headache they face is the mechanical failure of seals in dynamic environments. This can lead to premature downtime or reduced preventative maintenance (PM) intervals, both of which lead to a higher cost of ownership. Fortunately, tool owners have begun to implement seal designs better suited for these dynamic environments: Parker EZ-Lok is a proven solution.

Spiral Failure

picture of spiral o-ring failure

One of the more extreme forms of mechanical failure to be prevented is twisting and spiraling of an O-ring during operation. This occurs with O-rings in dovetail glands where one of the sealing surfaces is a door that opens and closes against the seal. The combination of stiction to the door and stretch in the gland causes the O-ring to roll and twist repeatedly with each cycle, resulting in permanent cyclic deformation. This means that a seal profile with a flat contact surface is vital for this type of dynamic function.

Other designs

The basic D-profile is the fundamental simple shape that serves as the basis of the EZ-Lok solution. The flat portion of the “D” holds the seal in place and prevents rolling, while the opposite, round contact surface focuses the sealing force and helps keep volume requirements at a minimum. These geometric features make for sound sealing function while preventing the drastic spiral damage seen so often in the industry.

picture of d-profile

A standard D-ring is still more limited by volume requirements than traditional seals like O-rings. In addition, a D-ring’s sharp corners can become difficult to install past the top groove radii if the seal is made much wider than the groove opening. On the other hand, a seal made any narrower would be easily removed without intention, such as that induced by stiction to the door. These reasons are why the basic D-profile alone is not the answer to these failure modes.

The Solution

picture of Parker EZ-Lok seal

The solution to these dilemmas is a unique D-shaped profile with a geometry that lends itself to the spacial constrictions of dovetail glands, prevents rolling, and locks into place: the Parker EZ-Lok seal. These seals are designed with special retention ribs placed with precise frequency around the seal circumference that allows for smooth installation and keeps the seal retained in the gland. This design also removes any tendency to stretch the seal during installation, which is often seen with more conventional seals.

The combination of retention ribs with a fundamental D-ring profile makes EZ-Lok the ideal geometry for effective use of the high-performance compounds typically required for aggressive semiconductor chemistries. EZ-Lok seals allow for lower cost of ownership through PM-minimization and reduced seal overhead costs, made possible by effective mechanical design. This is an example of how Parker’s effective design engineering can reduce the cost of ownership and bring premier solutions to the table.


For more information about Parker’s full suite of solutions and sealing products, contact Gallagher Fluid Seals’ engineering department.

Reduce Maintenance Costs When Sealing Dry Running Equipment

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s Website and was written by Nathan Wells, Application Engineer, Parker Engineered Polymer Systems Division.


My grandpa used to have a rusty, old air compressor in his shop. As a child, when my siblings and I would visit him, he’d use it to power air wrenches, grinders, and inflate flat soccer balls for us. I noticed it had a port labeled “ADD OIL DAILY” that was covered in the same thick layer of greasy dust as all the other unused junk in his shop. Knowing my grandpa, if asked about adding oil he probably would have said, “Oil is expensive. That’s how the companies get ya!” The compressor’s seals leaked so badly, you could hear the hissing even over the loud motor. I was certain one day it would explode.

picture of dry running equipmentPneumatic tools are common in factories, tool shops, and DIY garages around the world. Using compressed air for power is convenient, simple, and — when maintained properly — safe and efficient. However, air treatment costs can add up fast. Traditional rubber seals used in air tools require clean, low moisture, compressed air with the proper amount of lubrication added. Good Filter/Regulator/Lubricator systems (FRLs) cost as much as the tools themselves! So, what would happen if we didn’t have to provide pristine air?

Today we have the technology to create seals for tools which don’t require daily or even yearly upkeep. You’ll find these tools labeled “maintenance-free,” which sounds great to the guy responsible for maintenance. It sounds even better to the guy paying for maintenance … and to engineers designing tools who want to keep warranty costs down.

Seal materials for dry running

Early pressure seals were made out of leather. My grandpa’s compressor probably wasn’t that old, but even since his time, we’ve come a long way.

When I’m asked for seal recommendations in totally dry-running applications, my mind clicks to a material called PTFE (chemical name polytretrafluoroethylene). Most people know PTFE by the brand name Teflon® and are familiar with its use when applied to cookware as a high temperature, slippery, non-stick coating.

PTFE is a semi-hard plastic which feels slick to the touch thanks to its low friction properties. It’s considered self-lubricating because it leaves micro deposits on the sealing surface and reduces friction after just a few strokes. Because of this, it’s good for high-speed sealing and can operate completely dry.

By adding fillers to PTFE, seal manufacturers can tailor materials for greater suitability in meeting performance requirements for a wide range of conditions. String-like additives including fiberglass and carbon fiber increase pressure rating, wear resistance and seal life. Dry lubricant-type additives such as graphite or molybdenum disulfide (MoS2) further increase a seal’s ability to run without lubrication, and at higher speeds and pressures. In pneumatic medical, pharmaceutical, and food processing systems, clean grade mineral-based strengtheners may be used as additives.

PTFE seals for dry running equipment are available in several profile configurations:

Continue reading Reduce Maintenance Costs When Sealing Dry Running Equipment

What to Know, Avoid, and Consider When Planning Seals for Medical Devices

Seals are one of the most important components in many medical devices. While small in cost, seals for medical devices have a profound affect on the function of said device and the outcome of a medical procedure.

Engineered sealing solutions have advanced to meet the new medical device designs due both to new materials and to new processes for producing these seals. An understanding of the fundamentals of seal design, the tools available to assist in the manufacturing process and pitfalls to avoid will help in achieving a successful seal and medical device outcome.

Classifying the three basic seal designs

When approaching a new seal design, It is important to classify the seal based on its intended function. All seals fall into one of three distinct groups. While certain applications may combine more than one group, there is always one that is dominant. The three basic seal designs are:

Static — seal applications where there is no movement.
Reciprocating — seal applications where there is linear motion.
Rotary — seal applications where there is rotation.
Static seal applications are the most common and include those that prevent fluids and drugs from escaping into or out of a medical device. The seal design can range from basic O-rings to complex shapes. Static seals can be found in the broadest range of medical devices from pumps and blood separators to oxygen concentrators.

trocar design
New advances in trocar designs incorporating specialized seals allow multiple instruments to be inserted in the single trocar.

A reciprocating seal application with linear motion would include endoscopes that require trocar seals. These trocar seals are complex in design and allow the surgeon to insert and manipulate instruments to accomplish the medical procedure. These procedures range from relatively simple hernia repairs to the most difficult cardiac procedures. All of these minimally invasive surgeries employ endoscopes with seals that rely on seal stretch, durability and ability to retain shape during lengthy and arduous procedures. This particular seal application combines both reciprocating and rotary motion with the main function being linear motion.

A rotary seal application most commonly includes O-rings used to seal rotating shafts with the turning shaft passing through the inside dimension of the O-ring. Systems utilizing motors such as various types of scanning systems require rotary seals but there are many other non-motorized applications that also require rotary seals. The most important consideration in designing a rotary seal is the frictional heat buildup, with stretch, squeeze and application temperature limits also important.

Function of a particular seal design

What is the function of the seal? It is important to identify specifically if the design must seal a fluid and be impermeable to a particular fluid. Or will the seal transmit a fluid or gas, transmit energy, absorb energy and/or provide structural support of other components in device assembly. All of these factors and combinations need to be thoroughly examined and understood to arrive at successful seal design.

A seal’s operating environment

In what environment will a seal operate? Water, chemicals and solvents can cause shrinkage and deformation of a seal. It is important therefore to identify the short and long term effects of all environmental factors including oxygen, ozone, sunlight and alternating effects of wet/dry situations. Equally important are the effects of constant pressure or changing pressure cycle and dynamic stress causing potential seal deformation.

There are temperature limits in which a seal will function properly. Depending on the seal material and design, a rotary shaft seal generally would be limited to an operating temperature range between -30° F and +225°F. To further generalize, the ideal operating temperature for most seals is at room temperature.

Expected seal life – How long must the seal perform correctly?

Continue reading What to Know, Avoid, and Consider When Planning Seals for Medical Devices

VA179: Industry Leading High Temperature FKM

High Temperature FKM - VA179The O-Ring & Engineered Seals Division of Parker Hannifin Corporation, the global leader in motion and control technologies, recently announced the launch of VA179, a new extreme high temperature fluorocarbon (FKM) compound. VA179 is an innovative, 70 durometer rubber seal material providing increased high temperature limits while maintaining chemical resistance and low temperature sealing consistent with standard FKMs.

VA179 consists of a breakthrough rubber technology increasing the FKM continuous high temperature limit an additional 20°C (68ºF) over standard FKM materials on the market today. This provides a new industry sealing solution to long-term compression set issues for customers using traditional fluorocarbons and silicones.

“In markets such as aerospace, automotive, and heavy-duty, we are frequently challenged to expand the temperature capabilities of our rubber compounds,” says Nathaniel Sowder, aerospace, military and chemical processing business development engineer, O-Ring & Engineered Seals Division, “With the launch of VA179, we now have a solution that will reach higher temperatures without sacrificing the low temperature and chemical resistance attributes that make standard FKM such a popular choice.”

Continue reading VA179: Industry Leading High Temperature FKM

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