4-12-2

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Union Pacific 9000-series
UP 9000 2.jpg
The prototype, UP 9000, as preserved at the Los Angeles County Fairplex in Pomona, California.
Specifications
Power type Steam
Builder American Locomotive Company
Build date 1926–1930
Total produced 88
Configuration 4-12-2
UIC classification 2′F1′ h3
Gauge 4 ft 8 12 in (1,435 mm)
Driver diameter 67 in (1,702 mm)
Length 102 ft 7 in (31.27 m)
Weight on drivers 355,000 lb (161.0 t)
Locomotive and tender
combined weight
782,000 lb (354.7 t)
Fuel type Coal
Fuel capacity 42,000 lb (19.1 t)
Water capacity 18,000 US gallons (68,000 l; 15,000 imp gal)
Boiler pressure 220 lbf/in2 (1.52 MPa)
Cylinders Three
Cylinder size
  • Outside (2): 27 in × 32 in (686 mm × 813 mm);
  • Inside (1): 27 in × 31 in (686 mm × 787 mm)
Tractive effort 96,650 lbf (429.9 kN)
Factor of
adhesion
3.66
Career
Operator(s) Union Pacific Railroad
Class UP-1 through UP-5
Number(s) 9000–9087
Disposition One preserved, remainder scrapped
Front view of the same locomotive. The third cylinder and the mechanism that controlled it can be seen below the smokebox.

Under the Whyte notation for the classification of steam locomotives, 4-12-2 represents the wheel arrangement of four leading wheels, twelve coupled driving wheels, and two trailing wheels.

Other equivalent classifications are:
AAR wheel arrangement: 2-F-1
UIC classification: 2′F1′ (also known as German classification and Italian classification)
French classification: 261
Turkish classification: 69
Swiss classification: 6/9

This arrangement was named the Union Pacific type, after the only railroad to use it.

Only one type of 4-12-2 was built: the Union Pacific Railroad's 9000-series locomotives, 88 of which were built by ALCO between 1926 and 1930. These locomotives were used to increase the speed of freight trains in flat country, and were fairly successful, but were maintenance nightmares, largely because of their use of an inside third cylinder driving the cranked second driving axle between the frames. There was no inside valve gear to worry about, however. ALCO had obtained permission to use the conjugated valve gear invented by Sir Nigel Gresley. This system used two hinged levers connected to the outer cylinder's valves to operate the inner cylinder's valve. The 9000 class locomotives were the largest to use Gresley gear.

Between 1934 and 1940 eight of the first fifteen locos had their Gresley gear removed and were converted to a "double Walschaerts" valve gear which utilized a double eccentric (return) crank and second link on the right side (similar to the gear Baldwin used on its 3-cylinder experimental compound 4-10-2 #60000), which operated the valve for the inside cylinder. Union Pacific referred to this system as the "third link." The 4-12-2's constructed from 1928 utilized roller bearings in the Gresley lever bearings, thus none of these engines were converted. The pre-1928 engines not converted received the roller bearing levers in 1940, and no further conversions were made.

During design the third and fourth driving axles were planned to be "blind" (flangeless) in order to improve curve handling, but ALCO's lateral motion devices on the first and sixth axles (which allowed the axles to slide up to two inches to the side) made this unnecessary. They had the longest rigid wheelbase in North America, and until the Soviet Union built the 4-14-4 AA20-1 in 1934, the longest in the world. The trailing truck carried the same axle load as the drivers, which was unusual.

There has been debate as to whether the first driving axle of the 4-12-2 was cranked to provide clearance for the main rod connected to the second axle. Union Pacific drawings show no such crank on the first axle, and the Railway Age article says "The 67-inch drivers permit the use of a straight axle on the front drivers..." The spacing between the first and second axles was increased by 18 in (46 cm) to provide clearance. Based on the published dimensions, this means at its closest the centerline of the inside rod was 11.645 inches from the centerline of the first axle. (UP drawings reproduced in Kratville and Bush's "Union Pacific Type" books show the inside rod 113 inches long and the first and second driver axles 88 inches apart. The inside cylinder axis was inclined 9.5 degrees and was 32 inches above the plane of the driving axles at a point 181 inches ahead of the second driving axle, so the cylinder axis missed the centerline of the second axle by 1-11/16 inches. The rod centerline is closest to the axle when the crank is 54.49 degrees below horizontal.)

Union Pacific UP classes
Year Quantity Class Builder Union Pacific Number Notes
1926 1 UP-1 Alco 66544 Union Pacific 9000 Preserved
1926 14 UP-2 Alco Union Pacific 9001–9014 9004 to OWR&N 9708, then back to UP 9004
1928 15 UP-3 Alco Union Pacific 9015–9029
1928 8 UP-3 Alco Oregon-Washington Railroad and Navigation Company 9700–9707 to Union Pacific 9055–9062
1929 25 UP-4 Alco Union Pacific 9030–9054
1930 15 UP-5 Alco Union Pacific 9063–9077 to Oregon Short Line 9500–9514
1930 10 UP-5 Alco Union Pacific 9078–9087
Total 88

One example survives: Union Pacific 9000 (seen at right) at the Railway and Locomotive Historical Society's museum at the Los Angeles County Fairplex in Pomona, California.

References[edit]

  • Three Cylinder Steam locomotives maintained by Wes Barris
  • Drury, George H. (1983), Guide to North American Steam Locomotives, Waukesha, Wisconsin: Kalmbach Publishing Company, pp. 397–398, 404, ISBN 0-89024-206-2, LCCN 93041472 
  • Hollingsworth, Brian (2000). The Illustrated Dictionary of Trains of the World. London: Salamander Books Ltd. ISBN 1-84065-177-6. 
  • Kratville, William W.; Bush, John E. (1990). The Union Pacific Type, Vol. 1. Omaha, Nebraska: Barnhart Press. LCCN 90082171. 
  • Kratville, William W.; Bush, John E. (1995). The Union Pacific Type, Vol. 2. Omaha, Nebraska: Barnhart Press. LCCN 90082171. 
  • Westcott, Linn H. (1960). Model Railroader Cyclopedia - Volume 1: Steam Locomotives. Kalmbach Books. ISBN 0-89024-001-9. 

External links[edit]