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October 31, 2018
Compression fittings (sometimes called "lock-bush fittings") consist of a tapered, concave conical seat; a hollow, barrel-shaped compression ring (sometimes called a ferrule); and a compression nut which is threaded onto the body of the fitting and tightened to make a leakproof connection. They are typically made of brass or plastic, but stainless steel or other materials may be used.
Although compression connections are less durable than sweated connections, they are easy to install with simple tools. However, they take longer to install than sweated joints and sometimes require re-tightening to stop slow leaks which may develop over time. Because of this possible leakage, they are generally restricted to accessible locations (such as under a kitchen or bathroom sink), and are prohibited in concealed locations such as the interiors of walls..
Flared connectors should not be confused with compression connectors, with which they are generally not interchangeable. Lacking a compression ring, they use a tapered conical shaped connection instead. A specialized flaring tool is used to enlarge tubing into a 45º tapered bell shape matching the projecting shape of the flare fitting. The flare nut, which had previously been installed over the tubing, is then tightened over the fitting to force the tapered surfaces tightly together. Flare connectors are typically made of brass or plastic, but stainless steel or other materials may be used.
Although flare connections are labor-intensive, they are durable and reliable. Considered more secure against leaks and sudden failure, they are used in hydraulic brake systems, and in other high-pressure, high-reliability applications.
Flange fittings are generally used for connections to valves, inline instruments or equipment nozzles. Two surfaces are joined tightly together with threaded bolts, wedges, clamps, or other means of applying high compressive force.Although a gasket, packing, or O-ring may be installed between the flanges to prevent leakage, it is sometimes possible to use only a special grease or nothing at all (if the mating surfaces are sufficiently precisely formed). Although flange fittings are bulky, they perform well in demanding applications such as large water supply networks and hydroelectric systems.
Flanges are rated at 150, 300, 400, 600, 900, 1500 and 2500 lbs or 10, 15, 25, 40, 64, 100 and 150 bars of pressure. Various types of flanges are available, depending on construction. Flanges used in piping (orifice, threaded, slip-on, blind, weld neck, socket, lap-joint, and reducing) are available with a variety of facings, such as raised, flat, and ring-joint.
Slip-on flanges are slipped over the pipe and welded to provide strength and prevent leakage. This flange is less expensive than a weld neck and requires less accuracy when cutting pipe to length. Blind flanges are used to shut off a piping system or opening, while still allowing easy access for inspection.
A weld neck flange is joined to a piping system by butt welding. Although its long neck (or hub) makes it expensive, it reduces mechanical stress on piping by distributing stress between the base of the flange and the wall at the weld. Turbulence and erosion are reduced due to the matching size of the pipe and flange.
A socket flange appears similar to a slip-on flange, but its bore is counter-bored to accept pipe. A fillet weld around the hub of the flange attaches the flange to the pipe, with an interval weld added in high-stress applications. It is most frequently used in high-pressure systems, such as hydraulic and steam lines.
A lap-joint flange is similar to a slip-on, with room at the intersection of the bore and the flange face for a lap stub end. The face of the stub end conforms to the gasket face of the flange. It is used where sections of piping need to be dismantled quickly and easily for inspection or replacement.
Manufacturers such as Victaulic and Grinnell produce sleeve-clamp fittings which are replacing many flange connections. They attach to the end of a pipe segment via circumferential grooves pressed (or cut) around the end of the pipe to be joined. They are widely used on larger steel pipes, and can also be used with other materials.
The chief advantage of these connectors is that they can be installed after cutting the pipe to length in the field. This can save time and considerable expense compared to flange connections, which must be factory- or field-welded to pipe segments. However, mechanically fastened joints are sensitive to residual and thickness stresses caused by dissimilar metals and temperature changes.
A grooved fitting, also known as a grooved coupling, has four elements: grooved pipe, gasket, coupling housing, and nuts and bolts. The groove is made by cold-forming (or machining) a groove at the end of a pipe. A gasket encompassed by coupling housing is wrapped around the two pipe ends, with the coupling engaging the groove; the bolts and nuts are tightened with a socket or impact wrench. The installed coupling housing encases the gasket and engages the grooves around the pipe to create a leakproof seal in a self-restrained pipe joint. There are two types of grooved coupling; a flexible coupling allows a limited amount of angular movement, and a rigid coupling does not allow movement and may be used where joint immobility is required (similar to a flange or welded joint).
Crimped or pressed connections use special fittings which are permanently attached to tubing with a powered crimper. The fittings, manufactured with a pre-installed sealant, slide over the tubing to be connected. High pressure is used to deform the fitting and compress the sealant against the inner tubing, creating a leakproof seal.
The advantages of this method are durability, speed, neatness, and safety. Some crimped fittings are designed to be used with copper tubing, without requiring flux or filler metal. The connection can be made even when the tubing is wet. Although crimped fittings are suitable for drinking-water pipes and other hot-and-cold systems (including central heating), they are substantially more expensive than sweated fittings.
Pressfittings with either V and M profile (V Contour & M Contour) in stainless steel, carbon steel and copper are highly popular in Europe, and several manufacturers such as, Viega, Gebrit, Swiss Fittings, and ISOTUBI, distribute system dependent press fittings. When compared to other connection types, press fittings has the advantage of installation speed, and safety. Pressing a stainless steel fittings can be completed within 5 seconds with the correct equipment. Major pressing of fittings to pipes or other fittings is completed through electric press machines, however also mechanical press machines are available. Most of the major brands further have a plastic slip on the end of the press fittings allowing a simple identification if a press fittings has securely been installed. Further, the installation does not use any welding, thus press fittings, with appropriate and region specific certification, be installed for gas lines. Stainless steel and carbon steel press fittings can hold up to 16 bars of pressure.
Cast iron piping was traditionally made with one spigot end(plain) and one socket or hub end(cup shaped). In use, the spigot of one segment was placed into the socket of the preceding one and a ring of oakum was forced down into the joint with a caulking iron. After this the remainder of the space in the hub was filled up. Ideally, this would be done by pouring in molten lead, allowing it to set, and hammering it tightly with a caulking tool. If this was not possible due to position or some other factor the joint could alternatively be filled with lead wool or rope heavily packed down one layer at a time.
Cast iron DWV fittings are still used in premium construction because they muffle the sound of wastewater rushing through them,but today they are rarely joined with traditional lead joints. Instead, pipe and fittings with plain (non-belled) connections are butted against each other, and clamped with special rubber sleeve (or "no-hub") fittings.The rubber sleeves are jacketed with stainless steel clamps, which compress the rubber to make a tight seal around the pipes and fittings. Although the materials are not cheap, they are durable (the rubber is typically neoprene or PVC).
An advantage of flexible rubber fittings is that they can accommodate small misalignments, and can be flexed slightly for installation in tight locations. If necessary, the joints can be disassembled later, and the fittings and pipe may be reconfigured; however, it is often not customary to re-use the clamps and rubber sleeves.
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