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Piping foundations – relevant knowledge: Properties of plastic pipes Advantages: Good insulation properties. It is easy and cheap to process. It has acid and alkali resistance, is not prone to corrosion, and is suitable for use in areas where corrosive substances and gases are emitted. Disadvantages: Not suitable for areas with very high temperatures (below 60°C). Plastic pipes have a high coefficient of expansion, low thermal conductivity, and are poor at dissipating heat, which reduces the safe current capacity of the wires. The mechanical strength of plastic pipes is lower than that of metal pipes. Specifications of plastic pipes and their processing To cut PVC pipes, a steel saw, a cutting blade, or a PVC pipe cutter can be used. When using a steel saw, the teeth should face outward; apply force in that direction. When using a cutting blade, the teeth face toward the user, and force is applied as the blade is retracted. It is important to ensure that the cut surface is perpendicular to the pipe’s axis. The rough edges on the cut surface can be smoothed out using a file or a utility knife. The diagram shows the key points for cutting pipes. Production of bell mouths During piping, the bell mouth serves as a connector between the pipe and the connection box or valve; the working procedure is as follows: (For the shape and dimensions of the bell mouth, please refer to the diagrams and tables.) The pipe end should be made smooth, and heating should be applied evenly over a range of 1.5 times the pipe’s thickness from the end of the pipe (for a 1/2\" thick pipe, this is 2 mm, so 3 mm). After the tube end has softened, press it at a 30° angle onto a hard plate and rotate it once. Apply vertical pressure on the flat plate; after cooling, cut it at a length equal to 1.2 times the inner diameter (1/2\" is approximately 21.6 mm). Tube expansion When connecting PVC pipes together or to sockets, it is necessary to expand the pipe ends as shown in the diagrams and tables. The length over which the pipe is heated is 1.5 times its outer diameter (33 mm for 1/2\"); the expansion length is 1.2 times the outer diameter (26.4 mm for 1/2\"). To carry out this expansion, an expander made of wooden logs can be inserted into the heated section, and then removed after cooling. S-shaped bend: When a PVC pipe is connected to a junction box or connection box, there is a small distance between the hole in the box and the surface where the pipe is laid; therefore, an S-shaped bend (offset) should be made near the hole in the box. The procedure for this is shown in the diagram. Make a mark a about 2D from the tube end. Measure a length of L=2(d+1.5H) from point a, and mark it as b. Heat evenly between a and b; once it has softened, step on the area to the left of point b, and use the right hand (it is best to wear gloves) to lift the section at point a to a height corresponding to H. Make sure that the area to the right of point a remains parallel to the surface on which it is laid. Then, use the left hand to gently press on both sides of the bent area in order to prevent further bending. Finally, cool the bent area with a damp cloth. Right-angle bends: According to Article 224 of the electrical code’s regulations regarding internal wiring, the inner radius of the bend in the piping must be no less than 6 times the inner diameter of the pipe. The angle of the bend must be at least 90°, and there should not be more than 4 right-angle bends between two connection boxes; otherwise, it will make it difficult to pass the wires through. The calculation of the arc length for a right-angle bend is as shown in the figure: Arc length l = radius (r) × angle (θ) = (6×d + 1/2d + tube thickness) × π/2 = 1.57 × r. Taking a 1/2” PVC tube as an example, the arc length l = 1.57 × 12 cm = 18.8 cm. The procedure for making a right-angle bend is as follows: refer to the diagram (bending from box A to box B). Draw a horizontal and a vertical line from the two connection boxes; their intersection point is m. Insert the PVC pipe about 0.7 cm into the armor-piercing cartridge, and make a mark at point m on the opening of the cartridge. From point m, draw a line in the direction of box A with a length of r = 6d + D/2 ≒ 12 cm, and mark it as a. Mark the length of 18.8 cm, which is the folding amount from a, as b (or take a length of 18.8 cm – 12 cm = 6.8 cm in the opposite direction from point m). Use a blowtorch to heat at an angle of 30° between a and b until softening begins, then bend the pipe. Advantages of EMT tubes: Good corrosion resistance – uses zinc with a high purity and minimal alloy content. Moreover, the galvanized layer provides a quite strong corrosion-resistant protective film, thus giving the structure excellent rust resistance. The seam also has good corrosion resistance. After being formed into tubes, the wire pipes are coated with zinc through continuous melting; as a result, the seam areas are coated evenly just like the other parts, making rust formation less likely and ensuring good corrosion resistance. No further painting is required on the surface; the coated surface features a uniform zinc coating that gives it a beautiful silver color. Due to its shiny luster, it is referred to as WHITE. It can also blend in well with the internal fixtures in buildings and factories. Construction method for metal tube (EMT) pipes: (I) 90° bend (1) After inserting the metal tube into the retaining ring, pull it back by 0.5 cm, mark point 1, and use a one-time bending tool to bend it to 90°, as shown in Figure (a). (2) Mark point 2 and use the same one-time bending tool to bend it to 90° (be sure it is parallel to the first right angle and slow down the bending speed), as shown in Figure (b). (II) Small S bend (1) Mark the area on the metal tube where it contacts the panel surface. (2) Place the metal tube on the ground (with the flat side facing down) and make marks at 8 cm and 14 cm; draw a circle at 14 cm. (3) Start bending with the painted side facing up; at this point, there is a mark at 14 cm (which makes it less likely to bend incorrectly). Then replace the metal tube with the painting and bend at the mark at 8 cm. Introduction to Pipe Fittings: Copper faucets at 90 degrees, copper tees, copper connectors; plastic elbows, plastic tees, plastic faucets at 90 degrees, copper-plastic unions; plastic valve connectors. Tools: ◦ Ruler (60 cm), compass, tape measure, set square, angle grinder, level. Tools: ◦ Vise, plastic pipe scissors; thin pipe cutters, steel pipe cutters; thread formers, pipe wrenches; adjustable wrenches, open-ended wrenches; flat files, round files, half-round files, triangular files; hand saws, saw blades; pliers, diagonal pliers, needle-nose pliers, electrician’s pliers; spray gun, igniter. Pipe Processing: Cutting steel pipes (using a hand saw), cutting steel pipes (using steel pipe cutters); trimming burrs; cutting using a high-speed grinder; cutting plastic pipes, trimming burrs on plastic pipes; cutting and trimming copper pipes; threading steel pipes. ◦ Knobs, proper handling techniques; sleeves, lubrication (cutting oil); buttons, rotation; completion of threading (8–10 threads)