Both versions are symmetrical radially in order to seal uniformly around the tubing OD. One piece ferrules are often available as asymmetrical or symmetrical. To this end, it is also important that the ferrule have a sharp forward edge. A uniform, “line contact” compression around the entire circumference of the ferrule will create the most reliable seal. Additionally, the relative angles of the ferrule and the fitting body will determine how much linear motion is converted into radial compression, and what level of contact (“line contact” or “surface contact”) is made with the tubing. ![]() Both components must be tapered in a manner that allows the ferrule to compress properly as the nut is tightened, while maintaining axial alignment with the tubing. The shape of both the ferrule and the mating angle of the fitting body are critical factors in the reliability of a compression seal. Some of the key factors of the ferrule design include: Ferrule Shape ![]() Ferrules however, are specifically engineered to create an optimal seal against both the tubing and the fitting body. Typically, metal-to-metal seals are considered leak-prone (for example, metal pipe threads are often reinforced with pipe tape). Metal ferrules are attractive because they are stable over a wide temperature range, and they can bear compressive loads without relaxing. The majority of ferrules in the marketplace however, are manufactured from metals. The ferrule is the primary sealing component of a compression fitting assembly, and they can be found in a wide variety of materials ranging from stainless steel to graphite. Chief among these are fitting and ferrule design, tubing selection, and installation procedure. The success of compression fittings in a given application can depend on a number of factors. It is this radial compression that creates the leak tight seal between the fitting, ferrule, and tubing, and gives the compression fitting its name. As the ferrule(s) moves axially into the fitting body, the body’s angled shape radially compresses the end of the ferrule onto the outer diameter of the tubing. ![]() The functioning principle of each component also remains more or less the same between designs: tubing is inserted into the end of the fitting, and the nut/screw is tightened, forcing the ferrule(s) into the fitting body. Whether it’s the water heater in your home or a pipe transporting hazardous chemicals, all compression fitting applications have several traits in common: they require easy assembly, long life, and absolutely no leaks.Ĭompression fitting assemblies vary in design from manufacturer to manufacturer, but are all made up of the same three basic elements: a compression nut or screw, one or more ferrules, and a compression fitting body. Miniature compression fittings are found in applications ranging from chromatography and bomb detection instruments, to medical devices and inkjet printing. Particularly useful for their extreme temperature and pressure capabilities, and their compatibility with aggressive fluids, compression fittings can be seen in systems varying from gas lines in refineries, to the plumbing under your sink. Compression fittings are one of the most common and versatile methods of connecting metal or hard plastic tubing.
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