In the same way if eight " bolts are used, the pitch would require to be about 5", which is greater than five times the diameter. Using nine bolts, or adding to the thickness of cover would meet the case. EXAMPLES. Calculate the number and diameter of bolts for connecting the following flanges or covers :- 3 " EX. 1.-Pipes of 8" diameter, thickness steam pressure 100 lbs. per square inch above atmosphere. EX. 2.-Cover for condenser 9" diameter of hole, internal pressure 5 lbs. per square inch above atmosphere. EX. 3.-Cover for slide valve chest, size inside chest 124′′ × 6", steam pressure 120 lbs. per square inch above atmosphere. (48) Pipes.-Pipes for the conveyance of steam, gas, or water are made of wrought iron or steel, cast iron, and of copper, the latter being chiefly restricted to marine work. The thickness of cylindrical pipes to resist bursting may be easily found as follows, when the maximum pressure, diameter, and resistance of the material is known :— Let dp = internal diameter in inches (when the thickness is great, d, should equal the mean diameter). . = length of pipe or cylinder, neglecting flanges, in inches. t = Р = thickness of pipe or cylinder in inches. maximum internal pressure in lbs. per sq. inch. f = safe stress in the material in lbs. per sq. inch. Then the bursting effort is equal to Px dxl, and this is resisted by the tensile strength of the two sections of the shell, each being of length 7 and thickness t, the total resistance being 2 (lxtxfi). P.dp 2 ft In actual engineering practice the thickness of pipes, especi ally when made of cast iron, is always in excess of the thickness, calculated in this way in order to meet the requirements of manufacture. (49) Iron and Steel Pipes.-Wrought-iron or steel pipes or tubes are generally manufactured as a speciality, and are obtained by the users from the makers who guarantee them of given strength. They are usually made in lengths of from 12 to 16 feet. Tubes of 12" diameter may be used with a working pressure of 500 lbs. per square inch, the pressure increasing as the diameter decreases. It is, therefore, sufficient for the of this work to notice only the following proportions:— 1 to 23 3 to 41 to 6 purposes 7 Diameter in inches, Thickness in inches, (50) Cast-Iron Pipes.-The thickness of cast-iron pipes is a question of foundry possibilities rather than one of theoretical strength. It is impossible to cast thin pipes with any degree of uniformity, the result being that cast-iron pipes and cylinders are invariably much thicker than theoretically necessary. A workable thickness is given by taking the greatest resistance of the material as equal to 1,800 lbs. per square inch, taking care that the minimum thickness is not less than for short lengths, and for long lengths. The following are practical proportions for pressure up to 250 lbs. per square inch :— (51) Copper Pipes.-Copper pipes are made from malleable sheets and may be as thin as". The thickness for any diameter and working pressure may be found by taking the greatest resistance of the material as equal to 3,000 lbs. per square inch. The following are practical sizes for pressures up to 100 lbs. per square inch : - Diameter in inches, Thickness in inches, 1 to 6 1 to 1 8 to 12 12 to 18 The thickness of copper sheets is usually measured with the Birmingham Wire Gauge. (52) Pipe Connec Wrought iron or steel pipes are often connected by a simple screwed socket, as shown in Fig. 123. The pipe ends PP and the socket S are screwed with right- and left-handed threads, so that the two pipes are drawn closely together until the ends meet, a ring of packing being often inserted between them. The socket should embrace a length of each pipe equal to from 1 dp to 1 dp, and in thickness is equal to one and a-half times the pipe thickness. Figs. 124a, b, c, d, show standard forms of pipe connections. (53) Cast-Iron Pipes (a).-Here the flanges F F are cast with the pipes PP, a "fillet" of radius equal to the pipe thickness up to a maximum of 1" being cast at the junction of the flange and pipe. The flange thickness equals from 13 to 1.5 times the pipe thickness. As this is in excess of the thickness required from considerations of bolt diameter, the bolts used for cast-iron pipe flanges are generally smaller in diameter than the thickness of the flange. (54) Wrought-Iron Pipes (b).-Flanges, F F, of cast iron made thicker next the pipe by a spigot, S, in order to give a greater length of thread. Some makers are satisfied with simply screwing the flange tightly on, as in the lower pipe, others use "back nuts," B N, as shown on the upper pipe, which jamb against the back of the spigot, and make a more rigid joint. These nuts are better octagonal when of large size. The total depth of the flange and spigot is made about one and a-half to one and three-quarter times the flange thickness, when as on the lower pipe. In the upper pipe the depth should not be less than two and one-quarter times the flange thickness, in order to keep the back nuts clear of the flange-bolts and nuts. The back nuts do not follow the sizes of ordinary nuts. They need not exceed a thickness of " to ", and a size across the flats arranged to give a minimum width of metal of 8" to 9". The spigot diameter depends upon the nut, and should not be less than the size across the flats of the nut, due regard being paid to sufficient thickness of metal. Thickness of flanges need not be less than bolt diameter. (55) Copper Pipes (c).Flanges, F F, of gunmetal, made thicker by a beading, B, next the pipe, the flange and pipe being brazed together. Beading for pipes up to 8" diameter, from 1" thick x 5" deep to 5" thick x" deep. The flange thickness may be from three to four times the pipe thickness, and should not be greater than the bolt diameter. It is important to note that, although the general aim in designing flanges of pipes and + Fig. 124c. F F B valves is to keep the diameter as small as possible, yet in cases where there is a long range of horizontal piping, the flanges serve materially to stiffen the pipes and to prevent buckling. In such a case the diameter is often made larger than usual, and similarly with a valve having one flange bolted to a cylinder or condenser and the other flange supporting a line of piping where a rigid joint is very necessary. Also, the question of how near the bolts may be placed to the pipe is modified by whether the pipe is easily getatable, or placed where it is difficult to use a spanner. These points should always be looked to. (56) Union Joint (d).-This joint is used for small brass and copper pipes, where it may be necessary to frequently break and make the joint, as in connections to pressure gauges, portable pumps, &c. Each pipe is screwed fast into a socket, A and B, of which A is made with a screwed end and a nut part, N, for holding with a spanner, and B with a small collar or flange. A loose, partly covered nut, N', forms part of the connection B, which, screwing on to the screwed end of A, draws the two pipes tightly together against a ring of packing placed between the ends of A and B in the space marked p. The connections are of cast brass, and the nuts are made octagonal for compactness, and of a size across the flats equal to some size of Whitworth standard nut. (57) Elbows and Tee Pieces.-Lengths of piping are connected together at different angles by means of short bent lengths called "elbows," "bends," or "tee pieces.' An elbow or bend has usually two flanges at an angle to each other, and when fixed in a line of piping alters the direction of the line according to the angle. A tee piece has three flanges, and really consists of a short length of pipe connected at right angles to another length, and, therefore, resembling the letter T. It is |