Under the Whyte notation for the classification of steam locomotives, 2-10-2 represents the wheel arrangement of two leading wheels on one axle, usually in a leading truck, ten powered and coupled driving wheels on five axles, and two trailing wheels on one axle, usually in a trailing truck. In the United States and elsewhere the 2-10-2 is known as the Santa Fe type, after the Atchison, Topeka and Santa Fe Railway that first used the type in 1903.
Other equivalent classifications are:
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The 2-10-2 evolved from the ATSF 2-10-0 Decapod. The ATSF’s existing 2-10-0 locomotives, used as pushers up Raton Pass, encountered problems reversing back down the grade for their next assignments. The 2-10-0s, being unable to track around curves at speed, had to run very slowly to avoid derailing. Consequently, the ATSF added a trailing wheel to the engines, allowing them to operate successfully in both directions.[1]
These first 2-10-2 became the forerunners to the entire 2-10-2 fleets. Like all ten-coupled designs, the long rigid wheelbase of the driving wheels presented a problem on curves, requiring blind drivers, lateral motion devices and much play on the outer axles. To limit this problem, plus the weight of the rods, the driving wheels were generally small, up to 64 inches (1,630 millimetres), which in turn generated the problem of insufficient counterweights.[1]
There were two forms of 2-10-2, the 'heavy' locomotive and a 'light' version. The 2-10-2's inherent problem was the low speed restriction on the type, which was about 35 miles per hour (56 kilometres per hour). Further, the 2-10-2 had other inherent restrictions. The massive cylinders that were required on USA locomotives for high tractive effort had the result that no reasonable sized valves could admit and exhaust steam at a sufficient rate to permit fast running. In addition the 2-10-2, like the 2-6-2, had its main rod connected to the third axle, very near to the centre of gravity, which created a violent nosing action when operating at speed.[1]
In the USA the peak of the 2-10-2 design limitations was reached in 1926, and was overcome with the advent of the superior 2-10-4 design.[1]
2-10-2s were used in a number of countries around the world, including those in North America, Western Europe, China, the Soviet Union and South Africa.
In North America the 2-10-2 was produced between 1914 and 1930, after which its limitations became apparent and larger locomotives were built. About 2,200 were built, including about 500 of the two USRA WWI standard designs. The heaviest 2-10-2s were the ten built by Baldwin for the Reading circa 1931, weighing 451,000 pounds (204.6 tonnes) engine only. The Illinois Central 2800-class rebuilds probably had the highest calculated tractive effort for any two-cylinder steam locomotive at 104,000 pounds-force (462.6 kilonewtons), even though the weight on drivers was only 333,000 pounds (151.0 tonnes).[2]
The Baltimore and Ohio placed its first order for a 2-10-2 with Baldwin in 1914 (No. 6000). From 1914 to 1956 these B&O engines bore numbers commencing with 6, hence their nickname 'big sixes'. Known as the S class, there were several variant sub-classes. The engines were heavy and powerful and they held off the diesel-electrics until 1951, when they gradually began to be withdrawn and were finally all scrapped by 1959.[2]
Continental Europe saw a fair number of 2-10-2s, although the type was always less popular than 2-8-2s and 2-10-0s. A large number of European 2-10-2s were tank locomotives, taking advantage of the symmetrical nature of the arrangement. Examples on the German railway systems included classes BR84 and BR85, both standard designs built in 1935 and 1937 respectively, and class BR95, built in 1922 by the Prussian State Railways. From 1936 the German railways built 28 3-cylinder 2-10-2 tender freight locomotives of class BR45, which were the largest steam locomotives on the system.
Romania designed the 151.000 Class as freight locomotives, in order to serve CFR. These locomotives used a straightforward two-cylinder (650x720 mm) engine with 1500 mm diameter driving wheels and a total weight in working order of 123 tons. The heating surface of boiler was 254.8 m2 of which 98.5 m2 was superheated and the grate area was 4.72 m2. At 21,294 kgf (46,950 lbf) (208.82 kN) tractive effort, they were the most powerful steam locomotives built in Romania.[3]
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In Spain, the 2-10-2 wheel arrangement had one series of 22 units. Initially ordered for the Norte Co., the RENFE kept the entire series on hand. Built between 1941 and 1944 in La Maquinista Terrestre y Marítima factory in Barcelona for hauling heavy coal trains, they were amongst the most powerful steam locomotives in Europe. They had three cylinders but used simple expansion and were known as "Santa Fe" locomotives.
On Cape gauge, this wheel arrangement was first used by the South African Railways (SAR) in 1927. Two Class 18 steam locomotives, the most powerful non-articulated locomotives to see service on the SAR, were introduced on the line between Witbank and Germiston in an attempt to ease problems that were being experienced with increasingly heavy coal trains. It was designed by Colonel F.R. Collins, Chief Mechanical Engineer of the SAR from 1922 to 1929, and built by Henschel and Son in Germany. They were three cylinder locomotives, with their two outer cylinders using Walschaerts valve gear and the inner cylinder using Gresley conjugated valve gear that was actuated by the motions of the outer cylinders.[4][5][6][7][8]
One more 2-10-2 locomotive, the Class 20, was designed by A.G. Watson, Chief Mechanical Engineer from 1929 to 1936, and built by the SAR at its Koedoespoort shops in Pretoria in 1935. In 1950 the sole Class 20 was modified to an experimental condensing locomotive, equipped with a condensing tender that was ordered from Henschel in 1948. Beginning in 1951, tests with the condensing Class 20 were conducted in the Eastern Transvaal and the Karoo. The positive results of the condensing trials proved the viability of condensing locomotives in South Africa and led to the introduction of the Class 25 4-8-4 condensing locomotive fleet in 1953.[4][5][6][7]
In the Soviet Union 2-10-2 type locomotives were used to haul heavy freight trains. Two series were relatively common, the FD (for Felix Dzerzhinsky) with more than 3000 built through the 1930s, and the LV (Lebedyanskii, modified by the Voroshilovgrad factory).[9]
The FD class was developed from ALCO and Baldwin heavy freight locomotives imported to Soviet Russia, where they were designated as Ta and Tb class respectively. In 1958, 1,054 FDs were sold to China, where they worked until the 1980s. A much lesser number were sold to North Korea around the same time.[10]
The LV class was developed from the previous L-class 2-10-0 locomotive by the Voroshilovgrad factory. It used a feedwater heater to increase thermal efficiency and it was the most efficient freight steam locomotive in the Soviet Union with thermal efficiency of 9.3%. The first prototype was named OR18-01 (October Revolution factory, 18 tonne axle load). 522 LV-class locomotives were built. Several were preserved, including the first OR18-01 and the last LV-0522.
2-10-2s were the mainstay of Chinese steam, this being the arrangement of the Chinese QJ class locomotives, based in turn on the Soviet LV class, which were built until 1988 and were still in widespread service until the final steam runs in 2003.
Some of these QJs are finding their way to the United States for excursion service. In 2006, Multipower International, Inc. restored two Chinese QJ 2-10-2 steam locomotives to FRA Part 230 specifications and delivered them to Railroad Development Corp.[11]
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