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EDITOR’S CHOICE
Figure 6. A preassembled cartridge for a medium-pressure mechanical grip fitting ensures the ferrules and the nut are always properly aligned during installation.
Figure 5. For hydrogen applications in particular, leaks can increase the danger to consumers and technicians alike. That is why fittings must be able to handle vibrations without backing off.
fitting from loosening when vibration occurs (Figure 5). Double-ferrule fittings create long lines of sealing contact between the ferrules and the tube and allow for a particularly strong gas seal. Double ferrule designs are frequently used when leaks must be avoided at all costs.
MEDIUM-PRESSURE TUBE FITTINGS For leak tight gas seal and vibration resistance in applications up to 20,000 PSI, medium-pressure tube fittings can offer reliable performance and ease of installation. Medium-pressure tube fittings differ from compression-style fittings, as they feature a dynamic wedge that allows remarkable pull-ups by torque or a number of turns. A two-ferrule design provides a robust tube grip with enhanced vibration resistance and a leak-tight gas seal upon initial installation and each remake. Additionally, most medium-pressure mechanical grip fittings contain a preassembled cartridge holding both ferrules and a nut (Figure 6). The cartridge ensures that the ferrules are always properly aligned and installed according to best practices. This reduces installation times and keeps installation and assembly costs down. At the same time, the connection is more reliable and provides enhanced uptime for many applications.
CONE AND THREAD FITTINGS Lastly, cone and thread fittings are most often used in situations in which both medium and high pressure will be applied to the fitting. Typically, they are the connection of choice in most high-pressure situations across multiple demanding applications.
If cone and thread fittings are to be used, they must be paired with specific tubing that has
UKManufacturing Spring 2024
Figure 7. It is crucial to ensure there are no burrs, scratches, or gouges during tube fitting installations to prevent leaks from occurring.
thicker walls and higher pressure ratings. Ideally, cone and thread fittings should feature a gland, a collar, a port, and a weep hole, which allows technicians to ensure proper installation and find leaks if they occur. Unlike other fitting configurations, cone and thread fittings require specific tools to make leak-free connections, and technicians must apply lubricant during cutting to lower friction. Additionally, the tube must be properly coned and threaded before the fitting is introduced to the system. There must be no burrs, gouges, or scratches during installation (Figure 7), or the connection will not remain leak-free, which can be problematic particularly in small molecule gas applications such as hydrogen. After proper preparation, technicians should thread a collar onto the tubing and insert a gland nut into the fitting body before it is tightened. If the system regularly experiences shocks or vibrations, anti-vibration components can extend the life of the tubing when installed properly.
THE IMPORTANCE OF TRAINING Understanding the intricacies of various fitting technologies is only the beginning of your journey. Though you are now better equipped to choose the right fittings for your system, there is much more to know. Working with a trusted supplier who can provide additional training opportunities is critical to understanding the full complexity of tube fitting selection and installation. Ideally, such training should provide in-depth information on meeting the day-to-day challenges related to fluid system design, operation, and maintenance. The courses should also be hands-on and taught by experienced instructors to master tube fitting selection, installation, inspection, and troubleshooting. With a complete education about tube fittings, you will be prepared to make the right decision on which fitting most effectively meets your application’s requirements.
Swagelok Company
www.swagelok.com
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