Bostec XE Seals: 100% reliable drop-in replacement for C-seals

Drop-In Replacement — No Change To Your Gland

Bostec XE Seals Are Better:

Bostec XE-Seals are a drop-in replacement for C-seals and are guaranteed to seal 100% of the time! No need to alter your gland.  XE-Seals drop right in and seal first time, every time. If you are having c-seal problems, talk to us and we’ll find a solution for you.


Avoid These C-Seal Problems with Bostec XE Seals

  • C-seals are fussy and unreliable
  • First installation failures can be 40% or more
  • C-seals may require multiple attempts and heating to achieve leak tight.
  • Compression forces are too high
  • Hard to handle in production environments
  • Problems achieving surface finish, flatness and parallelism specs
  • CTE compatibility
  • C-seals are limited to 100º bake temperatures, which is often too low for true UHV
  • C-seal are very hard and often damage your flanges
  • C-seals have a single hardness value –– there is no way to modulate crush force
  • Long lead times to obtain


Key Benefits with Bostec XE Seals

1. Improved Leak Tightness: The primary concern with UHV applications is maintaining an extremely high-vacuum and low leak rate environment. Switching to XE-Seals achieves better leak tightness, reduces the risk of leaks and maintaining the integrity of the vacuum system.

2. Ease of Installation and Handling: XE-Seals are easier to install and handle and can streamline assembly processes and reduce the likelihood of errors during installation.

3. Enhanced Long-Term Stability UHV systems often operate continuously for extended periods, sometimes years, without interruption. Companies seek metal seals that offer greater long-term stability to minimize the need for maintenance and prevent unexpected failures that can disrupt operations.

4. Reduced Downtime and Maintenance Costs: Frequent failures or leaks with metallic C-seals can result in unplanned downtime and increased maintenance costs. By switching to XE-Seals, you will have reduced downtime and associated costs by minimizing the frequency of seal replacements and system troubleshooting.

5. Lower Cost: XE-Seals are almost always lower in cost than C-seals

6. Available in 6 to 10 Weeks: Bostec manufactures all its seals in the US and lead times are generally 6 to 10 weeks depending on the gasket material you choose.

7. Compatibility with Harsh Environments: XE-Seals can be produced in nickel, copper, aluminum, titanium and other metals capable of dealing with reactive gas and harsh environments.

8. Consistent Performance Across Applications: In some cases, our customers produce devices used in diverse applications or environments. XE-Seals offer consistent performance across different operating conditions and applications to maintain reliability and repeatability.

By addressing these key objectives, companies can mitigate reliability problems associated with metallic c-seals for UHV applications and achieve more consistent and dependable performance in their vacuum systems.



Why C-Seals are a problem:

C-seals are known to fail upon initial installation up to 40% of the time.  They are fussy to work with in production environments and require extreme levels of flatness, parallelism and perfection of the surface.  Companies find it difficult to manufacture glands that meet specification.

c-seal showing gaps created because seal is incapable of conforming

C-seals were developed in the late 1960s at CERN for use in harsh environments. The original design used an internal coiled spring to provide spring-back to absorb differences in thermal expansion. The concept seemed logical and millions of C-seals were installed in applications in aerospace, outer space, nuclear, oil and gas, and particle accelerators.

However, long term use uncovered fundamental problems with C-seals, the most significant being a high failure rate on first installation especially in sizes above 30mm. From a technician’s standpoint, C-seals are notoriously difficult to work with requiring delicate handling and special torquing patterns. At 120mm or more, the required gland surface finishes are difficult to produce and failure rates even with repeated attempts.

c-seal showing gaps created because seal is incapable of conforming

To understand the fundamental problem, you have to recognize the principle of gasket sealing is to prevent leakage by eliminating gaps between two mating surfaces. C-seals, with their hard outer shell, often inconel, are unable to conform to variations (undulations, machining marks, microscopic distortions, etc) in the mating flanges, leaving open gaps and therefore the junction leaks. For a seal to work, one side or the other must conform – either the seal molds itself to the flange or the flange must be distorted or dented by the seal. The gaps have to somehow be closed.

With C-seals, the rolled outer shell is too hard and rigid to conform to even small flange variations. The flange itself is structurally rigid because it has to be to perform its function and therefore neither side can adapt or mold itself to the other and the junction leaks.

c-seal showing gaps created because seal is incapable of conforming

Ideally, the gasket should do all the conforming so your flanges are not damaged. But C-seals are so hard (inconel) that flanges are routinely dented making them difficult to reuse. If the first C-seal fails and another one is tried, the flange has often been damaged by the first try and therefore has an even lower chance of sealing on the second try. C-seals are often the cause of their own problems. This is part of the fussiness technicians face with C-seals.

C-seal manufacturers specify extremely tight tolerances for flatness, surface finish and parallelism on the mating surfaces generally in the range of 2% of the seals height for each opposing side. Typical C-seals are around 0.090” in cross-section, which means the minimum specification is ±0.0018” flat and parallel. For a seal OD of 1” this tolerance is manageable, but for 2” or over, it becomes very difficult to machine. Over 4” OD, it’s not practical to even attempt for production parts.

The C-seal manufacturers make this requirement because they understand their own seals are incapable of conforming and filling gaps, so they insist your parts be at near perfect levels of finish, which is difficult for most manufacturing environments to produce. Flat and parallel to tenths adds enormous cost to manufacturing, and for flanges over 4” in diameter, the tasks can be nearly impossible.

To summarize, common C-seal complaints revolve around their installation difficulties and the stringent requirements for surface flatness and parallelism.

Common C-Seal Grievances

1. Failure on First Installation: C-seals have a high failure rate during the initial installation, with reported failure rates of more than 40%, often requiring multiple attempts, and occasional heating of flanges to achieve a leak-tight seal.

2. Bending Moment

3. Low Bake-Out Temperature: C-Seals are limited to a 100°C bakeout, which is insufficient for most applications where normal bakeout requirements range from 250°C to 350°C.

4. Difficulty in Achieving Surface Perfection: C-seals require extremely flat and parallel surfaces for proper sealing. Achieving the necessary level of surface perfection can be challenging for manufacturers, leading to production delays and higher costs.

5. Fussiness During Installation: C-seals are known to be fussy to work with during installation. Their design often requires precise alignment and careful handling, which can be time-consuming and labor-intensive.

6. Damage to your flanges

7. No springback

8. High Maintenance Requirements: Maintaining the required surface flatness and parallelism over time can be challenging, especially in dynamic environments or under harsh operating conditions. This can result in increased maintenance efforts and costs over the lifespan of the equipment.

9. No way to modulate crush forces: C-seals have a single crush value per circumferential inch and there is no way to modify the standard design to provide different force values or crush depths. XE and H-Seals can be adjusted for force and crush over a wide range of values either by altering the profile or penetration depth. Bostec’s seals provide much greater flexibility.

10. Stock size limitations:  Bostec specializes in producing seals to the exact size and force required for the given application. Bostec does not force customers to fit into stock sizes. All Bostec seals are custom designed to fit our customer’s exact requirements.

Our process for developing new XE or H-Seals for our customers

Until now, choosing the appropriate metal seal has meant selecting from a limited range of off-the-shelf CF gaskets or C-seals, usually with a larger footprint than necessary. Larger footprint means more and bigger fasteners and wasted space.

Bostec’s approach is the opposite. We start with conducting Force, Bake and UHV Tests.For applications were C-seals arebeing replaced with XE-Seals, we conduct force test on the existing C-seal and then match or reduce those forces with the XE drop in replacement.

When starting from scratch with a new design, we look at the available footprint and package size, how much room is available for fasteners and other limitations the metal seal has to accommodate.  We chose the appropriate seal profile based on the operating conditions and test values.


Force, Bake, UHV, UHP and Wear Testing

Bostec performs extensive force and UHV testing for each of our customer’s applications.  The purpose is to dial in the forces and validate the seals perform as intended.  Most of our customers have high imperative projects were failures are costly.  Outer space, radioactive medical isotopes, particle accelerators, aerospace components and so forth. Empirical testing allows

Bostec’s Force, Bake and UHV Lab is unique in the world, dedicated entirely to metal seal testing where we can conduct force tests to 1 million pounds total load and simultaneously validate UHV performance with or without bake, and conduct wearability tests for glands and knife edges.  Where required, UHV tests may also be combined with external pressure to simulate real-world high pressure environments.

For C-seal replacement projects, we start with developing a force profile of your existing C-seals.  To  accomplish this, we produce a replica of your junction (gland) and run multiple crush cycles using your existing C-seals.  We use calibrated digital force testing equipment for measurements and the empirical data produces a curve showing crush force vs compression from the unloaded state to full crush.

Based on that empirical force data, we produce XE replacement seals tuned to operate at higher or lower force values.  Most customers want lower forces and we can generally cut the crush force from 20% to 50% of your current loading.  The XE replacement seals are a drop-in replacement of the C-seal you have been using, the difference being the XE-Seals are 100% reliable.  Drop-in replacement means you do not need to change your existing gland.  The XE-Seal drops right in.

To validate your new XE seals, we can perform additional tests that include bake and helium leak testing to 2.5x10E-10 torr.  If required we can UHV test through the full room temperature to bake to cool-down cycle.

For H-Seal projects, we conduct the same force, bake and UHV tests, but with the objective of reducing penetration forces by tuning the knife angle and penetration depth.

Force testing advantages beyond compression force requirements

1. Optimized Seal Performance: By precisely measuring the compression force required for full contact metal-to-metal gland closure, customers can ensure optimal seal performance. This helps prevent leaks and ensures reliable sealing over the lifespan of the seal.

2. Enhanced Seal Lifespan: Force testing allows us to fine-tune the compression force of replacement seals to match or slightly reduce the force of the original C-seal. This optimization can help extend the lifespan of the flanges by minimizing wear and fatigue, ultimately reducing the frequency of replacements and associated maintenance costs.

3. Improved Efficiency and Cost Savings: Reducing the compression force required for sealing not only minimizes the size and number of fasteners needed but also reduces the overall load on the sealing system. This can lead to cost savings in terms of material usage, assembly time, and maintenance expenses.

4. Tailored Solutions for Specific Applications: Force testing enables customers to customize replacement seals to meet the specific requirements of their application. By fine-tuning the compression force, customers can address unique operating conditions, such as temperature variations, pressure fluctuations, or dynamic movements, to ensure optimal seal performance and reliability.

5. Consistent Quality Assurance: Implementing force testing as part of the manufacturing process ensures consistent quality and performance of replacement seals. Customers can have confidence that each seal meets the specified compression force requirements, resulting in reliable and predictable sealing performance across their systems.

6. Validation of Seal Design and Material Selection: Force testing provides valuable feedback on the effectiveness of seal design and the suitability of materials used in seal manufacturing. Customers can use this data to validate their design choices, identify areas for improvement, and make informed decisions for future seal procurement and development projects.

7. Enhanced Customer Satisfaction: Ultimately, force testing helps to deliver seals that meet or exceed customer expectations for performance, reliability, and cost-effectiveness. By providing optimized sealing solutions tailored to their specific needs, customers experience fewer issues, reduced downtime, and greater overall satisfaction with their sealing systems.

Overall, force, UHV and wear testing offers customers a comprehensive approach to seal optimization, ensuring consistent performance, efficiency, and cost savings across their operations.

In our force testing, we use calibrated digital force testing to determine closure force.  Values are read as pure force numbers, total pounds of force.  We do not use torque values from fasteners to determine total load, as torque values have too many variables such as friction, lubricant, thread size and pitch and so forth.


Additional advantages

1. Accuracy and Precision: Digital force testing provides precise and accurate measurements of the compression force required for seal contact. This allows for more reliable and repeatable results compared to other measurement methods, enhancing confidence in the data obtained.

2. Consistency Across Measurements Digital force testing ensures consistency in measurement techniques and equipment calibration, leading to uniform results across different testing sessions and operators. This consistency improves the reliability and reproducibility of the data, reducing variability and potential errors in the analysis.

3. Versatility and Customization Digital force testing systems offer flexibility in terms of test setup and parameters, allowing users to tailor the testing process to their specific needs and requirements. This versatility enables the testing of a wide range of seal configurations, materials, and operating conditions, enhancing the applicability of the results to real-world scenarios.

Using calibrated digital force testing to obtain pure force values offers numerous benefits, including improved accuracy, consistency, efficiency, and documentation capabilities.  These advantages contribute to better-informed decision-making, enhanced product quality, and increased confidence in seal performance and reliability.


Helium Leak Testing

We use helium leak testing to determine UHV leak rates and efficacy of the seal itself.  Our method is the first bake the part in the compression test to 200º C to drive off surface contaminants and water, then place the two compression flanges with a seal in between, then compress the parts to full metal to metal closure.  The flanges are connected to a helium leak detector with a turbo pump.  We pump down the assembly then bag the assembly and surround the parts with Helium and then have the leak detector tell us the leak rate with is expressed in atmosphere -cc/sec leak rate.  We are looking for 2.5 x 10E-11 or better which is considered true UHV.

Using helium leak testing to determine UHV leak rates and the efficacy of seals offers several benefits beyond confirming the seal’s ability to achieve true UHV conditions. Here are some additional advantages of this testing method:

Quantitative Leak Rate Measurement Helium leak testing provides a quantitative measurement of the leak rate, expressed in atmosphere-cubic centimeters per second (atm-cc/sec). This allows for precise assessment of seal performance and enables comparisons between different seals or sealing configurations.

Detection of Microscopic Leaks Helium leak testing is highly sensitive and capable of detecting even microscopic leaks that may not be detectable through other methods. This sensitivity ensures thorough evaluation of seal integrity and helps identify potential leakage points that could compromise UHV conditions.

Quality Assurance and Reliability The ability to verify seal integrity under UHV conditions through helium leak testing enhances quality assurance and reliability. Customers have confidence in the performance of seals knowing that they have undergone rigorous testing to ensure minimal leakage and adherence to UHV standards.

Compliance with Industry Standards Helium leak testing is often required to meet industry standards and specifications for UHV applications, particularly in sectors such as semiconductor manufacturing, aerospace, and scientific research. By demonstrating compliance with these standards, manufacturers can access new markets and assure customers of seal performance reliability.

Overall, helium leak testing provides comprehensive evaluation of seal performance, ensuring that seals meet stringent UHV requirements while also offering insights into manufacturing processes, quality control, and troubleshooting efforts. This method plays a critical role in maintaining the integrity and reliability of UHV systems across various industries.

Helium With Bake

Baking is a crucial step in the leak detection process for UHV systems, particularly when using helium leak testing. Baking serves several important purposes that enhance the effectiveness and accuracy of the testing:

Removal of Surface Contaminants and Water Baking the parts prior to leak testing helps drive off surface contaminants, such as oils, greases, dust, and other residues, that could interfere with the sealing surfaces or contribute to increased leak rates. Additionally, baking helps remove absorbed water molecules from the surface, reducing the potential for outgassing during testing, which could lead to false readings or higher background leak rates.

Improvement of Surface Cleanliness and Smoothness The elevated temperatures during baking promote the outgassing and desorption of contaminants from the surface, resulting in cleaner and smoother sealing surfaces. This enhances the effectiveness of the seal and reduces the likelihood of leaks caused by surface irregularities or imperfections.

Enhancement of Seal Performance By promoting surface cleanliness and smoothness, baking helps optimize the contact between the sealing surfaces, improving the effectiveness of the seal and minimizing leakage paths. This ensures more accurate and reliable leak rate measurements during helium leak testing.

Stabilization of Materials Baking can also help stabilize materials and reduce dimensional changes or shifts that may occur due to thermal expansion or contraction. This ensures consistency in the sealing geometry and minimizes variations in leak rates between different testing runs or conditions.

Prevention of Outgassing Outgassing of residual gases from materials or contaminants can occur at UHV conditions and contribute to background leak rates, making it difficult to distinguish between true leaks and background signals. Baking helps mitigate this by removing volatile compounds and minimizing outgassing during testing, resulting in more accurate and reliable leak rate measurements.

Overall, baking plays a critical role in preparing parts for helium leak testing in UHV systems by promoting surface cleanliness, improving seal performance, and reducing background signals. It ensures that leak rate measurements are accurate, reliable, and reflective of the true sealing integrity of the system. Therefore, baking is considered an essential step in the leak detection process for UHV applications.

Bostec XE Seals Size Chart

OD ±.001 inches
Nickel - 10pcs
Nickel - 100pcs
Nickel - 200pcs
Aluminum - 10pcs
Aluminum - 100pcs
Aluminum - 200pcs
OFS Copper - 10pcs
OFS Copper - 100pcs
OFS Copper - 200pcs

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