Tag Archives: o-ring

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

Installation of Linear Fluid Power 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 Nathan Wells, application engineer, Engineered Polymer Systems Division.


So, you’ve unboxed the shiny new Parker seals you ordered – now what?  Installing seals for the first time can be challenging without the right know-how and tools. In this article we’ll discuss best practices for seal installation in linear fluid power systems, and how to design your system to make seal installation fast and damage-free.

SEAL GROOVE STYLES

picture of closed rod seal groove

First, let’s look at three common groove styles:

•    Closed
•    Stepped, and
•    Open (or two-piece)

Closed groove

The closed seal groove fully encapsulates the seal and is the most common style used (see Figure 1).

Closed grooves are simple to machine and offer the best support for seals. Since seals in this configuration are surrounded by solid metal, without a well-developed process, installation can be challenging. Rod seals need to be folded to fit into internal (throat) grooves and piston seals must be stretched over the outside of the piston.

picture of cylinder head and piston seals

Notice how both designs shown in Fig. 2 and Fig. 3 utilize static seals (turquoise colored seal) on the opposing side of the dynamic, primary seals. Therefore, installation in either instance requires techniques and tools for both rod and piston seals.

Stepped groove

Typically utilized to ease seal installation, stepped grooves feature a reduced diameter on the low-pressure side of the seal as shown in Fig. 4 and Fig. 5.

picture of rod stepped groove

As shown, the “step” is just wide enough to hold the seal in place as the rod or piston strokes back and forth. This way, seals don’t have to be folded or stretched nearly as much when installing. This design works well for single seals only holding pressure from one direction, like Parker FlexiSeals™.

When using multiple seals stacked in series or in systems with bi-directional pressure, a closed or two-piece groove is needed for support on both sides.

Open and two-piece grooves

Open or two-piece grooves are used when the seal is either too small to be stretched or folded into a closed groove, or if it’s made of a material that doesn’t spring back after flexing.

Figures 6 and 7 show two examples of open grooves. Figure 6 uses a washer and a snap ring to hold the seal in place. Figure 7 uses a bolt-on cap. These groove designs can be used for bi-directional seals, too. As you can see, open grooves cost more to produce but seal installation is a snap.

picture of open rod groove

Open grooves also make removing the seal much easier – useful in systems which require periodic seal replacement. Continue reading Installation of Linear Fluid Power Seals

Reduce Downtime and Costly Seal Replacements: Seal Failure Diagnosis 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 William Pomeroy, applications engineer, Parker O-Ring & Engineered Seals Division.


There are many situations where an O-Ring may not last as long as one thinks that it should. When the expectation is realistic and yet the seal fails earlier than expected, Applications Engineering teams are often asked to help discover the seal failure mode(s).

Seal failure is often due to a combination of failure modes, making root cause difficult to uncover. When beginning a failure analysis, items usually asked for include: hardware information, how the seal is installed, application conditions (temp, fluids, and pressure exposure), and how long into the service that the seal failed. These details help bring the overall application into focus and enable a quick diagnosis to help resolve seal failures. In part one of the seal failure blog series, we will discuss compression set, extrusion, and spiral failure.

Compression set

  • picture of compression setCompression set is likely the most common failure mode for elastomer seals. Compression can be defined, or rather quantified, by the seals ability to return to its original shape after compression is removed. Zero percent compression set indicates that no relaxation (permanent deformation) has occurred, while 100% compression set indicates that total relaxation (seal no longer applies a force on the mating surface). When investigating material options, note that the lower the % compression set for a given compound, the more resilient the material is. However, it is extremely important to ensure you are making equal comparison in terms of time and temperature for the test conditions.
  • There are many potential causes for compression set.
    • Poor material properties
    • Improper gland
    • Fluid incompatibility
    • Temperature exposures above the recommended range for the material.

Extrusion and Nibbling

  • picture of extrusionThe driving force (pun intended) for this failure mode is the pressure load that the seal is exposed to. Extrusion most often occurs when a seal material deforms into the space between the bore and the outside of the tube (commonly referred to as the extrusion gap or “E-gap”). An approximation for the pressure rating for a seal can be determine by evaluating figure 3-2 of the Parker O-Ring handbook. The X-axis shows the size of the clearance gap (total gap, or diametral gap), and the Y-axis is the pressure load. The curves on the chart correspond to the hardness of the rubber. Extrusion can also occur due to gland overfill, when the deformation from compression of the seal fills the entire groove and lips over into the extrusion gap.
  • Face seals do not usually have an extrusion gap, so this orientation can achieve much higher pressure loads than a radial seal. Without a gap for the seal to extrude into, the risk of significant extrusion is highly diminished.
  • Extrusion in radial seals can by combated by reducing the clearance gap or by adding a back up ring.

Spiral Failure

  • picture of spiral failureSpiral failure can be more simply described as the O-Ring rolling in the groove. This failure more is most common in dynamic reciprocating O-Ring applications. However, spiral failure can also occur during installation. An image of spiral failure is unique, and relatively easy to diagnose, but the root cause of spiral failure can sometimes be difficult to pinpoint. Uneven surface finish, poor lubrication, side loading, eccentricity, or perhaps stroke speed can all contribute to spiral failure.

Check out Parker’s neat video about Seal Failure Modes:

Parker and Gallagher Fluid Seals can help diagnose seal failures and the best sealing solutions for your application.

Stay tuned for Part 2 in this series.


For more information about how Gallagher Fluid Seals can help you, contact our engineering department today.

How to Properly Measure an O-Ring

Measuring an O-Ring is quite simple when you have the right tools at your disposal. All that is required is a clean, level surface; an o-ring; and a measuring device such as a caliper or other measuring tools such as cones, gauges, and size charts.

Directions to Measure an O-Ring

To measure an O-Ring, following the directions below:

  1. Place your o-ring on a flat surface clean of debris.
  2. Determine the inside diameter (ID) and outside diameter (OD) of the o-ring. The o-ring dimensions chart below illustrates where on the o-ring each dimension is measured.
  3. Measuring the width, or cross-section (CS), can be tricky and is measured by lightly pressing the caliper ends onto O-ring as shown in section A-A.

For more information on O-ring sizes click to see the JIS B 2401 Standard O-Ring Size Tables.

Dimensionally specifying an o-ring can typically be done with just two dimensions, the inner diameter (ID) and the cross-section (CS). Occasionally, an O-ring may be specified with an outer diameter (OD) and cross-section or an inner diameter and outer diameter. If two of the three dimensions are known, the third can be calculated using the formulas shown below.

O-Ring Dimensions

O-Ring Dimensions

 

O-Ring Dimension Calculations

o-ring dimension calculations


The original article can be found on Dichtomatik’s website. Gallagher Fluid Seals is a distributor of Dichtomatik, a brand of Freudenberg.

For more information about measuring o-rings or determining the best o-ring to use, please contact Gallagher’s engineering department.

A Short Guide for Rubber Seals & Design

Rubber seals are used in numerous industries to prevent the unwanted leakage of liquids and gases in various components such as pumps, valves, pipe fittings, and vacuum seals, to name only a few. However, all seals are not created equally. Rubber seal design consists of several elements to ensure that the seal delivers optimal performance in the given environment.

One of the most common types of industrial rubber seals, the O-ring, relies on mechanical compressive deformation to act as a barrier between mating surfaces, thus restricting the flow of fluid in predetermined areas. Several factors must, therefore, be taken into account in O-ring seal design to sustain the compressive force and maintain an effective seal.

Key Design Considerations

Rubber seals are available in a large number of material compositions, each with its own set of advantages and limitations. The selection of the appropriate material involves the consideration of specific factors including:

Dimensional Requirements

To provide a proper seal, the O-ring needs to be compressed between the mating surfaces. The deformation caused by this compression is what prevents fluid leakage. To achieve the proper compressive force and deformation, the cross section of the O-ring needs to be sufficiently larger than the gland depth.

As the two mating surfaces press together, the O-ring seal compresses axially and exerts an equal and opposite force at the top and bottom ends of the seal. If the O-ring is too small, the seal may not compress when the surface come together. On the other hand, an O-ring that is too large will over pack the gland and disrupt the connection between the mating surfaces.

Friction

Friction considerations are essential in dynamic applications – in situations that involve relative movement between the mating surfaces.

In reciprocating applications, these movements can generate frictional forces which may cause failure due to abrasion or extrusion and successive nibbling of the seal. In rotary applications, friction may generate excessive heat and seal expansion due to the Joule effect. In both of these applications, proper groove design, along with appropriate lubrication and speed of operation can help to avoid these issues. Silicone and related materials such as Fluorosilicone, liquid silicone rubber, and medical grade silicone are often avoided in dynamic applications due to their low abrasion/tear resistance.

temperature considerationTemperature

Long-term exposure to excessive heat can cause inappropriate rubber seals materials to deteriorate physically or chemically over time. Excessively high temperatures can cause specific materials to swell and harden, resulting in permanent deformation. Conversely, overly cold temperatures may cause material shrinkage and result in leakage due to loss of seal contact, or insufficient compressive force due to stiffening of the rubber compound.

Therefore, the appropriate seal material should be selected to withstand the expected temperature ranges of the environment. The length of exposure should also be considered. For example, would the temperatures be sustained in short intervals or at sustained levels?

Pressure

Differential pressures tend to push rubber seals (o-rings) to the low-pressure side of the gland causing it to distort against the gland wall. This action blocks the diametrical gap between the mating surfaces and results in the formation of a positive seal. Excessively high pressures can cause softer O-ring materials to extrude into the diametrical gap resulting in permanent seal failure and subsequent leakage. To avoid this situation, seal materials that operate optimally within the expected temperature range should be selected.

chemical compatibilityChemical Compatibility

One of the most critical considerations for rubber seals design and material selection is determining the material’s resistance to exposure to specific chemicals. Some fluids can react negatively with certain materials while having little to no effect on another. For example, Nitrile is highly resistant to petroleum-based oils and fuels, while the use of Butyl is avoided in applications with exposure to petroleum and other hydrocarbon-based solvents due to its poor resistance.

Remember to keep dimensional requirements, friction, temperature, pressure, and chemical compatibility in mind when it comes to customizing a rubber seal solution for your application.


For more information about custom seal designs or to see which seal might be the best fit for your application, contact Gallagher Fluid Seals.

The original article can be found on Precision Associates website, and was written in January 2019.

Engineered Materials and Sealing Solutions for Flow Batteries

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.
Original content can be found on Parker’s Blog.


Sealing can often be a frustrating challenge when dealing  with flow batteries. Determining what materials are compatible with certain chemistries or developing a profile that provides optimal sealing under available compression can be a time-consuming task for those outside the sealing industry. A trial and error approach can have a significant overall cost impact through multiple prototype iterations, prolonged testing, and ultimately, delaying product commercialization.

Specialized support

Parker’s design and material engineers can provide support to your team in the critical, early stages of product development. With hundreds of engineered elastomeric materials to choose from, our team can identify and recommend a compound that works with your specific electrolytes or other fluids. With the exceptionally long lifetime requirements of flow batteries, our homogeneous rubber provides the elasticity needed to handle the many charge-discharge cycles the battery will see in its life.

Continue reading Engineered Materials and Sealing Solutions for Flow Batteries

TetraSeals: Alternate Sealing Solution

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.
Original content can be found on Parker’s Blog.


TetraSeal: An Alternate Sealing Solution When an O-Ring Isn’t Working

Parker TetraSeals

Our applications engineering team takes more than a few calls each month where the O-ring is leaking, either immediately or after just a short time in service. Once we drill down to the details, we learn the failure mode is an improperly sized groove and O-ring. It isn’t all that uncommon for a groove to be cut in a flange and a novice designer learns the hard way that standard O-rings cannot fit in just any groove geometry. For hardware that has already been machined, frustration ensues as the caller learns the O-ring solution requires tooling. Tooling can have a lead time of at least a month to cut and can cost thousands of dollars. Parker offers a TetraSeal® solution, which often does not require tooling and can be made of many of the same materials used for O-rings.

Benefits of TetraSeals

The TetraSeal is a circular precision-cut seal with a square cross-section. Unlike O-rings which require a unique mold for each material family and size, TetraSeals are extruded, cured and machine cut to the target thickness. Our manufacturing facilities in both Spartanburg, South Carolina and Goshen, Indiana are tooled in a variety of interchangeable extrusion dies, making this type of seal an easily sourced seal solution without the lead time and cost of a custom molded O-ring.

Continue reading TetraSeals: Alternate Sealing Solution

Innovative Solutions Improving Seal Retention

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.
Original content can be found on Parker’s Blog.


Seal Retention - Pre-applied PSA

We receive many requests from customers asking for recommendations on how to retain seals in an application. One of the most popular “quick fixes” is to apply liberal amounts of adhesive to a standard O-ring type product without respect to groove shape or sealing function. However, Parker OES provides a wide array of sealing technologies, offering innovative solutions to accommodate the challenging and vast sealing needs of our customers.

Replacing RTV with Pre-Applied PSA

A customer had been using a standard O-ring product on an outdoor electronic device. This part was sealing the external edge of the enclosure and meant to keep out water and dust. The enclosure was plastic injection molded so this extreme edge had irregular geometry to accommodate the molding process. The original proposal was to shove O-ring cord in place and adhere it down with RTV (Room Temperature Vulcanization) so that it did not fall out during assembly. This left a rust colored stripe exposed on a  consumer device due to fitment issues. Parker’s proposal was to replace the O-ring cord with a custom hollow extrusion that fit the available space and allowed complete closure, thus not exposing the seal to be visible. The RTV process was replaced with PSA (Pressure Sensitive Adhesive) that was preassembled to the seal and allowed for quick and clean placement during assembly and retention for any maintenance needed.

Innovative Solutions Improving Seal Retention, Hollow Teardrop Profile Seals, O-Ring & Engineered Seals Division

Continue reading Innovative Solutions Improving Seal Retention

NEW! Elastomer Failure Modes – Part 3

Failure ModesGallagher recently published its Failure Modes of Elastomers in the Semiconductor Industry White Paper, now available for download on our site.  This white paper discusses common issues that occur with elastomer seals in the semiconductor industry. The excerpt below is the third section of our new white paper, discussing O-Ring Stretch, Chemical Attack, Plasma Cracking, and Permeation.  To download the entire white paper, visit our Resources Page, or click on the image to the right.


Failure Modes of Elastomers in the Semiconductor Industry

Failure ModesHigh performance elastomers are found in many applications in the semiconductor industry (see paper titled Perfluoroelastomers in the Semiconductor Industry). Though perfluoroelastomer (FFKM) seals are formulated to meet the highest performance requirements of integrated circuit (chip) manufacturers, even these elastomers can’t solve every sealing application nor will they last forever in service. Additionally, end users need to understand subtle performance differences between perfluoroelastomers in the same product line. For example, one product may be better at minimizing particle generation while another may be better for high temperature services.

Continue reading NEW! Elastomer Failure Modes – Part 3

How To Install an O-Ring in any Application

O-Rings continue to be the most widely utilized sealing product.  While the ‘Donut’ shaped profile has by and large been kept intact since their inception, continued elastomeric development has pushed o-ring temperature and chemical compatibility to limits unimaginable several decades ago.

Typically, O-Rings fail due to adverse effects of a number of factors, from improper installation and lubrication to incorrect size and design.  The collection of videos below will help you minimize installation errors that may lead to failure (be sure to bookmark this page for future reference).


How To Install an O-Ring – Standard Male Gland

Continue reading How To Install an O-Ring in any Application