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The Pennsylvania Railroad's K4s 4-6-2 "Pacific" (425 built 1914–1928, PRR Altoona, Baldwin) was their premier passenger-hauling steam locomotive from 1914 through the end of steam on the PRR in 1957. Attempts were made to replace the K4s, including the K5 and the T1 duplex locomotive, but none was really successful, and the K4s hauled the vast majority of express passenger trains until replaced by diesel locomotives. The K4s was not powerful enough for the heavier trains it often pulled from the mid-1930s onward, so they were often double or even triple headed. This was effective, but expensive—several crews were needed. The PRR did have the extra locomotives, many having been displaced by electrification. It is recognized as the State Steam Locomotive of Pennsylvania. On December 18, 1987, Pennsylvania Governor Robert P. Casey signed into law House Bill No. 1211 naming the PRR K4 as the “official” state locomotive, according that title to both K4 survivors, 1361 and 3750. == Development == The K4s was designed under the supervision of PRR Chief of Motive Power J.T. Wallis, assisted by Chief Mechanical Engineer Alfred W. Gibbs and Mechanical Engineer Axel Vogt, as one of a pair of classes with the L1s 2-8-2 "Mikado", sharing a boiler and other features. Some inspiration came from the large experimental K29s Pacific built in 1911 by the American Locomotive Company. Also influential was Gibbs' design for the successful E6 4-4-2 "Atlantics", from which the K4s inherited its heat-treated, lightweight machinery, its cast-steel KW trailing truck, and much of its appearance. The K4s design increased grate area from previous classes' . The boiler barrel was fatter than previous classes, and the increase in heating surface and boiler size gave the class good steam-generating capability. Equipment on the prototype, built in 1914, was conservative and included a screw reverse (power reverse would soon be added), a small 70-P-70 tender holding only of water and 12½ tons of coal set up for hand firing, a wooden cowcatcher pilot, a square-cased, old-fashioned headlight and piston tailrods (soon to go). The K4s design was successful enough that it influenced other locomotive designs, and not only those of other PRR locomotives. London and North Eastern Railway Chief Mechanical Engineer Nigel Gresley incorporated much of the boiler design (including the tapered shape) into his famous Class A1 Pacific.〔(【引用サイトリンク】 title=LNER Encyclopedia - The LNER A1 and A3 Gresley Pacifics )〕 A World War I era prototype had distinctive "chicken coop" slat pilots, while the Post-War versions had modern pilots. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「PRR K4s」の詳細全文を読む スポンサード リンク
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