are to be joined. The purpose of dielectric fittingsuniform plastic state, joining the componentsis to curtail galvanic or electrolytic action. Thetogether, and then allowing the two surfaces tomost common dielectric fittings are the union,fuse into a homogeneous bond as the materials coolcoupling, and bushing.to room temperature.Fittings are identified by the sizes of pipe thatare connected to their openings. For example, a3- by 3- by 1 1/2-in. tee is one that has twoopenings for a 3-in. run of pipe and a 1 1/2-in.reduced outlet. If all openings are the same size,only one nominal diameter is designated. Forexample, a 3-in. tee is one that has three 3-in.openings.Joints and ConnectionsThere are various methods of joining pipes forwater distribution systems. Each method used isdesigned to withstand internal (hydrostatic)pressure in the pipe and normal soil loads if jointsand connections are belowground. Some of thesemethods produce the types of joints andconnections described below.FLARED AND SWEATED JOINTS.— Thesejoints are generally used with copperpipeandtubing. The end of a copper pipe is formed intoa funnellike shape so that it can be held in athreaded fitting when a line joint is being made.This method is called FLARING, and the resultis called a FLARED JOINT. A SWEATEDJOINT is made with soft solder instead of threadsor flares. In plumbing, copper pipe or tubing isoccasionally fused by heating with a gas flame andsilver-aIloy filler metal called SILVER BLAZING(also called HARD SOLDERING).SOLVENT WELDED, FUSION WELDED,FILLET WELDED, THREADED, ANDFLANGED JOINTS.— These types of joints arecommon to plastic pipes. In the production ofa SOLVENT WELDED JOINT, a solvent cementwith a primer is used. Before solvent is applied,the pipe and fitting must be thermally balanced(caused to have similar temperatures). Thisprocess should not be undertaken when thetemperature is below 40°F or above 90°F or whenthe pipes are exposed to direct sunlight.FUSION WELDED JOINTS are produced bythe use of a gas- or an electric-heated welding tool.The process consists of simultaneously heating themeeting surfaces of the pipe and fitting to aFILLET WELDED JOINTS are made by theuse of a uniform heat and pressure on the weldingrod during application of the bead. This processcan also be applied to repair leaks inthermoplastics.In plastic pipes, THREADED JOINTS arecommonly used for temporary and low-pressurepiping since threading reduces the pipe wallthickness. Only certain heavy pipes can bethreaded with a special strap wrench. Teflon tapeis often used for pipe joint compound when thismethod of joining pipes is used.FLANGED JOINTS are extensively used forprocess lines that are dismantled frequently.Plastic pipes are joined together by the use ofplastic flanges with soft rubber gaskets.BELL-AND-SPIGOT AND MECHANICALJOINTS.— These types of joints are mostcommonly used with cast-iron pressure pipe andfittings for water mains. These service lines arejoined by the use of lead, lead wool, or sometimesa sulfur compound. Mechanical joints are madewith rubber sealing rings held in place by metalfollower rings that are bolted to the pipe. Theseare designed to permit expansion and contractionof the pipe without injury to the joints.THREADED PIPE JOINTS are commonlyused on galvanized steel, galvanized wroughtiron,and black-ironpipe. The processincludes connecting threaded male and femaleends. Nontoxic compounds are used for t breadlubricant on water pipes, while powdered graphiteand oil are used for steam pipes.ValvesValves are devices that are used to stop, start,or regulate the flow of water into, through, orfrom pipes. Essentially, valves consist of a bodycontaining an opening and a means of closing theopening with a valve disk or plug that can betightly pressed against a seating surface aroundor within the opening. Many different valvedesigns are available; however, only the three mostcommon types of valves will be discussed here.They are the gate, check, and globe valves.8-6
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