. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. hick?iess of Pipes.—The strains which pipes of this nature have tostand are due to internal pressure, bending, expansion, sudden shocks,and possibly, also, a crushing strain by the creation of a vacuum. Thethickness of the pipes to withstand a pressure due to a head of 80 of course easily be got at, but seeing that the sudden shocks whichmight arise from the quick closing of the valves and the tardy actionof the safety appliances cannot be ascertained with any degree of
. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. hick?iess of Pipes.—The strains which pipes of this nature have tostand are due to internal pressure, bending, expansion, sudden shocks,and possibly, also, a crushing strain by the creation of a vacuum. Thethickness of the pipes to withstand a pressure due to a head of 80 of course easily be got at, but seeing that the sudden shocks whichmight arise from the quick closing of the valves and the tardy actionof the safety appliances cannot be ascertained with any degree of accuracy,we decided to err on the side of safety, and basing ourselves on theknown results obtained at other installations of a similar character inFrance, commenced with a thickness of 4 mm. and increased it graduallyup to 8 mm., and for the lower half of the pipes used double rivetedjoints. The pipes themselves are in mild steel, each 3 metres long withflanged joints, and are bolted together. The joints are made withtarred cord. Safety Appliances.—In order to prevent the possible formation of [PLATE Fig. 314.—Pierrefitte Electric Power Station : Con-struction of Intake Canal. {To face page 4S6. THE PIERREFITTE ELECTRIC POWER STATION. 487 a vacuum in the pipes and their consequent collapse, a blast pieceis fixed at the upper end close to the intake chamber, shown in fig. 312,which is simply a small chimney rising above the water-level, and whichwould permit the entrance of air if the gratings became choked. After the pipes were laid, with the exception of the middle one, theexpansion as between midnight and midday with the pipes empty wasfound to be 30 mm. = i^ in., and a double diaphragm expansion jointof the form shown in fig. 315 was put in at this point. Seeing, however,that the temperature of the river water is practically the same all theyear round, it is probable that the expansion with the tubes full willnever reach the amount provided for. The tubes are
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