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steam locomotive[′stēm ‚lō·kə¦mōd·iv]
a locomotive that uses a steam engine as its power source. The basic components of a steam locomotive are the steam boiler, steam engine, and undercarriage. Supplies of fuel, water, and lubricants are usually stored in a tender attached to the locomotive; in tank locomotives, these supplies are located in the locomotive itself. Combustion of coal, fuel oil, combustible shale, peat, wood, or other fuels in the firebox of the steam boiler generates heat; the heat is transferred through the firebox walls and through five tubes and flues to the boiler water, which is converted into steam. In order to increase locomotive efficiency, the steam is superheated and the temperature is significantly increased. The steam engine converts the thermal energy into the mechanical energy of the pistons that move back and forth in steam cylinders; a crank and connecting-rod assembly transfers this motion to the driving wheels. The undercarriage of the locomotive includes the frame, wheel pairs with axle boxes, leading and trailing trucks (with one or two wheel pairs), spring suspension, and coupling mechanisms.
The first steam locomotives were built in 1803 and 1814 in Great Britain by R. Trevithick and G. Stephenson, respectively. The first steam locomotive designed in Russia was built by E. A. Cherepanov and M. E. Cherepanov in 1833. Steam locomotives remained the most important means of transport for over a century, until replaced by electric and diesel locomotives everywhere in the 1950’s. Although the production of steam locomotives ended in the USSR in 1956, the locomotives are still used on some minor railroad lines and in industrial enterprises. Low efficiency was the principal reason for the replacement of steam locomotives by other types of locomotives; thermal efficiency of the best models did not exceed 9 percent, with average efficiency measuring 4 percent.