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A water joint is any device or procedure used to facilitate the joining of water pipes or the inclusion of ancillary equipment while preserving the integrity and continuity of the pipe circuit. Water pipe joints may be permanent or removable depending on the application and type of pipe involved. These joints may be rigid or flexible or even include bellows type expansion elements to provide for increases in water pressure. Water joints may include no external parts and rely on welding, brazing, or soldering of the pipes or fittings alone or consist of separate joining elements. Water joints should be able to carry the same pressure as the rest of the pipe circuit without leaking or experiencing mechanical failures.
Water pipe systems are typically made up of many separate sections of piping and numerous pieces of ancillary equipment such as valves, pressure compensation bellows, flow meters, back-flow protectors, and access port fittings. The average water pipe installation also changes direction or elevation frequently and will have many branches, splits, or extensions along its route. All these deviations and additions require a water tight joint between different pipe sections, fittings, and external equipment. The type of joint used depends on a number of factors. These include pipe size, pipe material, system pressure, and whether or not the joint or fitting will require periodic removal or maintenance.
There are several distinct types of water joint each having its own benefits and particular area of application. The two main classifications of water pipe joints are permanent and removable. Permanent water joints include welded, brazed, and soldered unions and are generally used on smaller copper water pipes and very large steel distribution mains. The welded water joint on large mains pipes is typically a part of a system of prefabrication of pipe sections and is generally carried out off-site prior to installation. Steel water pipes may, however, be welded in-situ to effect repairs or system additions.
Smaller local copper pipe systems are often joined by brazing or soldering the pipes and fittings together. If correctly carried out, a welded, soldered, or brazed water joint is often the strongest and most resilient of all joints. Removable joints typically consist of flanges, clam-shell, and two part compression fittings. A flange water joint consists of two similar discs which are placed on the ends of the pipes to be joined. A packing element is introduced between the two and they are bolted together. This pulls the two flanges tightly up against one another, thereby forming a watertight joint.
Compression and clam-shell joints are typically two part fittings with internal compression seals. One half is located on each pipe end and are screwed together, thus compressing the seal element and forming a watertight joint. This type of joint is quick to replace should the seals become worn or damaged and allows for easy extension of the pipe circuit or the inclusion of other fittings. Simple single element sleeve joints are also often used on steel pipes and consist of a simple threaded sleeve sealed with hemp twine or PTFE tape. The most important defining characteristic of all water joints is their ability to carry the system pressure without leaking or allowing the ingress of contaminants and air.