3ths at one side and gths at the other, and of course the least thickness governs the strength of the pipe. And again, there are in most cases shocks arising from the closing of cocks, &c., against which it is necessary to provide adequate strength. In thin pipes, therefore, the determination of the thickness becomes a practical question, and we must obtain an empirical rule from experience. The rule may take the following form :— In which D = the diameter of the pipe in inches. Table 24 has been calculated by this rule, and we have also given the approximate weights, from gas-pipes in which the pressure is practically nothing, up to 1000 feet of water. Engineers usually specify the weight of their pipes rather than the thickness, leaving the founder to fix that for himself, which long practice enables him to do with considerable precision. Of course absolute correctness cannot be attained, and should not be expected; a margin should be allowed, say one pound to the inch, either way; so that, for instance, a 10-inch pipe for 100 feet head, specified to weigh 4 cwt. 2 qrs. 10 lbs., as per Table 24, should not be rejected if its real weight is between 4 cwt. 2 qrs. 0 lbs. and 4 cwt. 2 qrs. 20 lbs., &c. Founders consider this to be a fair allowance for variation in weight. (83.) "Proportions of Socket-pipes."-The joints of waterpipes are usually made by sockets and spigots run with melted lead; and this is the best mode. Such pipes are easy to cast, and consequently cheap, the joints are more easily made than with flanges, and they admit a considerable departure from the strictly straight line which is sometimes very convenient. But to allow for this the sockets must be made of larger diameter than is necessary where the line is straight, and for this reason, perhaps, sockets are frequently made larger than they should be for making a good joint. For ordinary cases inch in thickness or inch in diameter will suffice for pipes of 3 inches diameter and under; say from 3 to 10 inches; and for larger sizes. Table 25 gives the general proportions for socket-joints, weight of TABLE 25.-Of the PROPORTIONS of JOINTS, &c., for CAST-IRON SOCKET-PIPES. lead, &c.: we have also added the average cost of laying pipes, including excavating the ground and making good the same; this will vary of course with the nature of the ground and the cost of labour in different localities. In Table 26 we have given the weights of socket-pipes and connections by Bailey, Pegg, and Co., of Bankside, Southwark : by reference to Table 24 it will be seen that these pipes are of a weight and strength suitable for about 150 feet head in the larger sizes, and 250 feet in the smaller ones. (84.) "Proportions of Flange-pipes."-Flange-pipes are not very often used for water, for reasons already given; but they are convenient for temporary purposes, where the joints have to be frequently broken. Table 27 gives the best proportions for the flanges, bolts, &c., which will be found to differ considerably from those adopted by many makers. The flanges of cast-iron pipes are frequently made excessively large in diameter and very light in metal. India-rubber rings form the most convenient kind of joint for flange-pipes. TABLE 27. Of the PROPORTIONS of CAST-IRON FLANGE-PIPES. inches. inches. Diameter of inches. Diameter of Circle of Bolts. inches. No. of Bolts. 1층 51 3344 ៖ (85.) "Strength of Lead Pipes."-The strength of lead pipe may be calculated by Barlow's rule (81), taking the cohesive strength of drawn lead at 2745 lbs. per square inch, as determined by direct experiment. Lead pipes are made of various weights to suit the varying requirements of practice; taking medium weights, and deducing the thickness therefrom, we obtain the following Table, in which the safe working pressure is taken at th of the bursting strain : Diameter of pipe Weight of pipe, lbs. per foot .. 1 11 11 12 2 1.331 471 872 804 33 6.0 6.75€ 0 232 183 174 151 152 140 122 116 (86.) "Power of Horses, &c., in raising Water."-The power of men, horses, &c., in raising water varies with the duration of the labour. The following Table gives the number of gallons raised 1 foot high per minute, with common deep-well pumps, and the mean velocity in feet per minute. A good high-pressure steam-engine should raise 3300 gallons 1 foot high per minute per nominal horse-power; the friction of the pumps being compensated by the excess of the indicated power over the nominal. (87). "Rainfall."-The depth of rain in this country varies very much with the locality; the east coast is the driest, the annual rainfall being in Northumberland about 28.67 inches, diminishing thence gradually to 23 in Norfolk and to 19.8 in Essex, which is the minimum. Thence southward and westward it gradually increases to 25.6 in Kent, 30.64 in Sussex, 38.75 in Dorset, 48.3 in Devon, and 50·6 in Cornwall. The midland districts have a medium fall: Middlesex 24·1, Leicester 26.0, Hereford 29 27, Cheshire 31.3, &c., &c. 66 Heavy Rains."-For town drainage and other purposes, we require to know the maximum fall of rain during storms. find that in 1 5 15 30 45 We 1.33 inches. which is at the rate per hour of 12 9 4 3.6 3.3 3.25 1.8 "Rain-water Tanks."-Where it is desired to utilize as much as possible of the rain falling on a building, the minimum size of tank becomes an important but complicated question. Taking a place with 24 inches annual rainfall, we have evidently an allowance for a regular consumption of 2 inches per month. But there may be a drought in which for one month no rain falls, and the tank must have 2 inches in store to supply the deficiency. There may also be a wet month with 6 inches of rain, and as only 2 inches is consumed, 4 inches must be stored. The tank must therefore hold 2 +4 6 inches, or th of the annual rainfall. Again, for two months we require 4 inches, but the rainfall varies from 14 to 7 inches, and the tank must hold (4 – 14) + (73 · 4)= 6 inches, as before. For three months we require 6 inches, but the rainfall varying from 2.4 to 8.7 inches, the tank should hold (62.4)+(8·76) = = 61.000A |