About PTFE o-rings and spring-loaded PTFE history as following:
In dynamic applications requiring sealing at low to moderate speeds and pressures, design engineers replace poorly performing elastomeric O-rings with spring-loaded PTFE “C-ring” seals.
When O-rings and other traditional sealing methods don’t work, diagnostic and drug delivery device engineers are taking a new, more cost-effective approach to boosting the performance of their existing equipment designs: PTFE “C-Ring” spring seals.
C-seals were originally developed for diagnostic instruments using a piston reciprocating at 5 feet per minute operating in a water bath at approximately 100°F. Operating conditions are mild, but with large tolerances. The original design called for an elastomeric o-ring to seal the piston, but the o-ring could not maintain a permanent seal, causing the device to leak.
After the prototype was built, the engineers started looking for alternatives. U-rings or standard lip seals, commonly used in pistons, are not suitable due to large radial tolerances. It is also impractical to install them on full-stage recesses. The installation requires too much stretching, which leads to deformation and premature failure of the seal.
In 2006 , NINGBO BODI SEALS .,LTD came up with an experimental solution: a canted helical spring wrapped in a PTFE C-ring. Printing works exactly as expected. Combining the low friction properties of PTFE with a streamlined boot geometry, “C-Rings” provide a reliable, permanent seal and are smoother and quieter than O-Rings. In addition, C-rings are suitable for full-stage o-rings, which are generally not recommended for inelastic materials. Thus, the C-ring can be installed without changing the original equipment design or using any special tools.
The original C-seal was two years old. The use of C-rings improves product performance and extends equipment life by reducing downtime and maintenance costs.
Medical imaging equipment, insulin pumps, ventilators, and drug delivery devices often use O-rings to seal short axial spaces. But when extreme radial deflection capabilities are required, O-rings cannot compensate for this, often resulting in wear, permanent deformation, and leaks. Despite these shortcomings, engineers continue to use o-rings because other solutions (eg U-cups, lip seals) cannot meet radial deflection requirements and typically require more axial space than o-rings.
The C-ring is different in that it can fit into the smaller axial space normally provided for an O-ring, while standard seals cannot. In addition, C-rings can be fully customized to suit the needs of the application. It can be configured with an ultra-thin and flexible lip for cryogenic applications or a thick lip for dynamic applications where the seal requires more wear resistance.
Because C-rings allow both rotational and reciprocating motion, they are a versatile solution for a wide range of products that require low to medium speed sealing, including medical robotics, portable medical devices, and probe/tubing connectors. C-rings allow unusually large radial tolerances—at least five times greater than standard seals of the same cross-section. The tolerance range depends on the ambient pressure, the type of medium and the surface treatment conditions. C-rings also work well in static applications where components need to be protected from environmental contaminants.
By removing the PTFE material from the original C-ring boot design, the engineers were able to increase its elasticity and flexibility. As a result, C-rings have proven to be more stretchable and flexible than originally expected, making them suitable for non-circular applications. C-rings have been used in drug delivery pumps with oval pistons. Because the seal lip can be made from virgin PTFE or filled PTFE, the C-ring is an extremely versatile seal compatible with metal and plastic parts.
C-rings, originally designed for use with water-based diagnostic tools, consist of PTFE-jacketed helical springs. But C-rings can also be made using helical band springs as activators. By replacing canted helical springs with helical band springs, C-rings can provide very high sealing contact pressure, ideal for cryogenic or static applications.
Bal Seal Engineering calls its C-ring “the perfect seal for an imperfect world” because of its ability to provide extended service life in environments where gaps, surface finishes and other design characteristics vary widely. While there is no perfect seal, the versatility and customizability of C-rings certainly makes them an interesting and potentially useful option in some medical and diagnostic devices. This is a relatively lightweight seal ideal for low pressure (<500 psi) and low speed (<100 ft/min) applications where low friction is required. For these environments, C-rings can provide a better sealing solution than elastomeric O-rings or other standard seal types, offering designers the ability to increase service life and reduce noise levels without costly equipment modifications.
David Wang is Global Marketing Manager for Medical Devices at Bal Seal Engineering. An engineer with over 10 years of design experience, he works with OEMs and Tier 1 suppliers to create sealing, bonding, electrical conductivity and EMI solutions that help set new standards in equipment performance.
The opinions expressed in this blog post are solely those of the author and do not necessarily reflect the views of MedicalDesignandOutsource.com or its employees.
Chris Newmarker is the Managing Editor of WTWH Media’s life sciences news sites and publications, including MassDevice, Medical Design & Outcommerce and more. An 18-year-old professional journalist, a veteran of UBM (now Informa) and the Associated Press, his career spanned from Ohio to Virginia, New Jersey and, most recently, Minnesota. It covers a wide range of topics, but in the last decade its focus has been on business and technology. He holds a bachelor’s degree in journalism and political science from The Ohio State University. Reach out to him on LinkedIn or email cnewmarke
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Post time: Aug-10-2023