Document LgmBVnx9zXZD248MGDEkkQae5

Heating Ventilating Air Conditioning Guide 1938 threads are used. To facilitate drainage, some elbows have the thread tapped at an angle to provide a pitch of the connecting pipe of 34 in. to the foot: These elbows are known to the trade as pitched elbows and are commercially available. Malleable iron fittings, like brass fittings, are cast with a round instead of a flat band or bead, or with no bead at all. Fittings are designated as male or female, depending on whether the threads are on the outside or inside, respectively. Flanged fittings are generally used in the best practice for connecting all piping above 4 in. in diameter. While screwed fittings may be used for the larger sizes and are satisfactory under the proper working con ditions, it will be found difficult either to make or to .break the joints in these large sizes. A number of different flange facings in common use are plain face, raised face, tongue and groove, and male and female. Cast-iron fittings for 125 lb pressure and below are normally furnished with a plain face, while the 250 lb cast-iron fittings are supplied with a Jfj-inch raised face. The standard facing for steel flanged fittings for 150 and 300 lb is a Jfg-inch raised face although these fittings are obtainable with a variety of facings. The gasket surface of the raised face may be finished smooth or may be machined with concentric or spiral grooves often referred to as serrated face or phonograph finish, respectively. The dimensions of elbows, tees and crosses for 125 lb cast-iron screwed fittings are given in Table 7, whereas the dimensions for 125 lb cast-iron flanged fittings are given in Tables 8 and 9. For low temperature service not to exceed about 220 F, a number of paper or vegetable fiber gasket materials will prove satisfactory; for plain raised face flanges, rubber or rubber inserted gaskets are commonly employed. Asbestos composition gaskets are probably the most widely used, particularly where the temperature exceeds 250 F. Jacketed asbestos and metallic gaskets may be used for any pressure and tem perature conditions, but preferably only with a relatively narrow recessed facing. WELDING Erection of piping in heating and ventilating installations by means of fusion welding has been commonly accepted in the past few years as a competitive method to the screwed and flanged joint. Since the question of economy of welding as against the use of screwed and flanged fittings is dependent on the individual job, the use of welding is generally recom mended on the basis of a greatly reduced cost of maintenance and repair, of less weight resulting from, the use of a lighter-weight pipe, and of increased economy in pipe insulation, hangers, and supports rather than on the basis of any economy that might be effected in actual erection by welding. Fusion welding, commonly used in erection of piping, is defined as the process of joining metal parts in the molten, or molten and vapor states, without the application of mechanical pressure or blows. Fusion welding embraces, gas welding and electric arc welding, both of which are com monly used to produce acceptable welds. 366 Chapter 18. Pipe. Fittings, Wedding Welding application requires the same basic knowledge of design as do the other types of assembly, but in addition, requires a generous know ledge of. the sciences involved, particularly as to welding qualities of metal, their reaction to extremely high. temperatures, and the ability to determine and use only the best quality, welding rods. This requirement applies equally to employer and employee with the employer accepting Table 7. Tentative American Standard Dimensions of Elbows, 46 Deg Elbows, Tees, and Crosses (Straight Sizes) for 125 Lb Cast-Iron Screwed Fittings 1--A-H Elbow prr_ * f*-A - H 1i i u W1 tee ELBOW A Nominal Pips Silk CENTER to End, Elbows, Tees and Cbossxs cB E Center to End, 45 Deo Elbows Length of Thread Min. Width of Band, Min. F Inside Diameter of Fitting Min Max. <7 a Metal Thickness, Mm. Outside Diameter of Band. Mm. M . 2 2H 3 3H 4 5 6 8 10 12 14 O.D. 16 O.D. 0.81 0.95 1.12 1.31 1.50 1.75 1.94 2.25 2.70 3.08 3.42 3.79 4.50 5.13 6.56 8.08 9.50 10.40 11.82 0.73 0.80 0.88 0.98 1.12 1.29 1.43 1.68 1.95 2.17 2.39 2.61 3.05 3.46 4.28 5.16 5.97 0.32 0.36 0.43 0.50 0.58 0.67 0.70 0.75 0.92 0.98 1.03 1.08 1.18 1.28 1.47 1.68 1.88 2.00 2.20 0.38 0.44 0.50 0.56 0.62 0.69 0.75 0.84 0.94 1.00 1.06 1.12 1.18 1.28 1.47 1.68 1.88 2.00 2.20 0.540 0.584 0.675 0.719 0.840 0.897 1.050 1.107 1.315 1.385 1.660 1.730 1.900 1.970 2.375 2.445` 2.875 2.975 3.500 3.600 4.000 4.100 4.500 4.600 5.563 5.663 6.625 6.725 8.625 8.725 10.750 10.850 12.750 12.850 14.000 14.100 16.000 16.100 0.110 0.120 0.130 0.155 0.170 0.185 0.200 0.220 0.240 0.260 0.280 0:310 0.380 0.430 0.550 0.690 0.800 0.880 1.000 0.93 1.12 1.34 1.63 1.95 2.39 2.68 3.28 3.86 4.62 5.20 5.79 7.05 8.28 10.63 13.12 15.47 16.94 19.30 VI .LUC icsjjuijsiDinry. thus the employer should select his welding mechanics with good judgment, provide them with first-class equipment and tools, arrange for their training and use of acceptable workmanship standards, and at regular intervals subject their work to prescribed tests. Industry will not accept the employment of mechanics of undetermined ability nor on the basis of past experience. Neither does industry accept the statement that a weld is only as good as the workman who makes it. The control Codes now in process of adoption will be the law governing 367