Америкалық K4 4-6-2 локомотивтерінің тарихы

Class of 425 American 4 6 2 locomotives

The Pennsylvania Railroad (PRR) K4 4 6 2 "Pacific" (425 built 1914–1928, PRR Altoona, Baldwin) was its 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. However, the low factor of adhesion of K5s meant that they were limited in their pulling power. By contrast, the T1s were very successful but suffered from greater maintenance costs, wheel slip due to poor springing, and inexperienced crews. The T1s also came too late in the game for steam traction. As such, the tried and tested K4s held their role as the PRR's primary express locomotives for thirty to forty years. The K4s hauled the vast majority of express passenger trains until they were replaced by diesel locomotives. The K4s were not powerful enough for the heavier trains they often pulled from the mid 1930s onward, so they were often double headed or even triple headed, sometimes with early Atlantics and E6s. This was effective, but expensive, and several crews were needed. The PRR did have the extra locomotives, many having been displaced by electrification east of Harrisburg. The two preserved K4s Nos. 1361 and 3750 were designated as Pennsylvania's official state steam locomotives on December 18, 1987, when Pennsylvania Governor Robert P. Casey signed into law House Bill No. 1211.

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. A World War I era prototype had distinctive "chicken coop" slat pilots, while the postwar versions had modern pilots.

The PRR experimented extensively with its K4s fleet, trying out streamlining, poppet valves, smoke deflectors, driving wheel types and others.

Several K4 locomotives had streamlining applied over the years, to varying degrees. All were later removed, restoring the locomotives to their original appearance.

Locomotive #3768 was clad in a shroud designed by famed industrial designer Raymond Loewy in February 1936. This was a very concealing, enveloping streamlined casing that hid most of the functionality of the steam locomotive, leading to its nickname of "The Torpedo" by train crews. Clay models of Loewy's design streamlined K4s and conventional K4s were tested in a wind tunnel for smoke lifting ability by Alexander Klemin of the Daniel Guggenheim School of Aeronautics of New York University (CMP). Of 24 variations, 4 were chosen for wind tunnel tests to determine the final design. At first, the locomotive was not painted in standard Dark Green Locomotive Enamel (DGLE) but instead in a bronze color. It was later refinished in DGLE. A matching tender ran on unusual six wheel trucks. Like most streamlined steam locomotives, the shrouds impeded maintenance and the covers over the wheels were later removed. For a time, the locomotive was the preferred engine for the Broadway Limited.

These four locomotives were streamlined in 1940 and 1941 with simpler, closer fitting casings that hid less of the steam locomotives' workings, In that sense, they were similar to Henry Dreyfuss's casings for NYC Hudsons. According to an interview with John W. Epstein, Special Projects Manager and vice president, Raymond Loewy & Assoc., these four streamlined K4s were designed by Raymond Loewy but, due to WWII, there was no publicity about it. PRR #1120 and #2665 were streamlined in 1940 for the South Wind, a named passenger train equipped and operated jointly by the Pennsylvania Railroad, the Louisville and Nashville Railroad, the Atlantic Coast Line Railroad (later Seaboard Coast Line) and the Florida East Coast Railway. The South Wind began operations in December 1940, providing streamliner service between Chicago, Illinois, and Miami, Florida. PRR No. 3678 and No. 5338 were streamlined in 1941 for The Jeffersonian, one of the PRR's premier, all coach trains between New York and St. Louis. They were also seen hauling the Broadway Limited (New York to Chicago), Liberty Limited (Washington to Chicago), and the Trail Blazer (New York to Chicago) occasionally. During World War II, these four locomotives formed a streamlined steam engine fleet within the PRR system, with another five locomotives that were also designed by noted industrial designer Raymond Loewy; they were the PRR S1 #6100, PRR Q1#6130, T1's #6110 and #6111; and K4s #3768. Streamlined shrouding of these four K4s Pacific locomotives was removed after 1950, together with PRR K4s #3678.