4-12-2

Union Pacific 9000-series
UP 9000 2.jpg
The prototype, UP 9000, as preserved at the Los Angeles County Fairplex in Pomona, California.
Type and origin
Power typeSteam
BuilderAmerican Locomotive Company
Build date1926–1930
Total produced88
Specifications
Configuration:
 • Whyte4-12-2
 • UIC2′F1′ h3
Gauge4 ft 8 12 in (1,435 mm)
Driver dia.67 in (1,702 mm)
WheelbaseLoco & tender: 91.50 ft (27.89 m)
Length102 ft 7 in (31.27 m)
Axle load59,000 lb (26,762 kg; 27 t)
Adhesive weight354,000 lb (160,572 kg; 161 t)
Loco weight496,500 lb (225,209 kg; 225 t)
Tender weight310,599 lb (140,885 kg; 141 t)
Total weight807,099 lb (366,094 kg; 366 t)
Fuel typeCoal
Fuel capacity42,000 lb (19,051 kg; 19 t)
Water cap18,000 US gallons (68,000 l; 15,000 imp gal)
Firebox:
 • Firegrate area
108.25 sq ft (10.057 m2)
Boiler pressure220 lbf/in2 (1.52 MPa)
Heating surface:
 • Firebox
591 sq ft (54.9 m2)
Superheater:
 • Heating area2,560 sq ft (238 m2)
CylindersThree
Cylinder size
  • Outside (2): 27 in × 32 in (686 mm × 813 mm);
  • Inside (1): 27 in × 31 in (686 mm × 787 mm)
Performance figures
Tractive effort97,664 lbf (434.4 kN)
Factor of adh.3.63
Career
OperatorsUnion Pacific Railroad
ClassUP-1 through UP-5
Numbers9000–9087
Retired1953 - 1956
PreservedOne preserved (No. 9000), remainder scrapped
DispositionNo. 9000 on static display at the RailGiants Train Museum

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

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

Only one type of locomotive with a 4-12-2 wheel arrangement 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.

In this front view of the same locomotive the third cylinder and the mechanism that controlled it can be seen below the smokebox.

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 the longest in the world until the Soviet Union built their 4-14-4 locomotive in 1934. 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 in (170 cm) 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 in (29.58 cm) from the centerline of the first axle. (UP drawings reproduced in Kratville and Bush's "Union Pacific Type" books show the inside rod 113 in (290 cm) long and the first and second driver axles 88 in (220 cm) apart. The inside cylinder axis was inclined 9.5 degrees and was 32 in (81 cm) above the plane of the driving axles at a point 181 in (460 cm) 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 Alco order number Alco serial numbers Union Pacific Number Notes
1926 1 UP-1 B-1684 66544 Union Pacific 9000 Preserved
1926 14 UP-2 B-1684 67024–67037 Union Pacific 9001–9014 9004 to OWR&N 9708, then back to UP 9004
1928 15 UP-3 B-1706 67581–67595 Union Pacific 9015–9029
1928 8 UP-3 B-1708 67596–67603 Oregon-Washington Railroad and Navigation Company 9700–9707 to Union Pacific 9055–9062
1929 25 UP-4 S-1646 67944–67986 Union Pacific 9030–9054
1930 15 UP-5 S-1701 68490–68504 Union Pacific 9063–9077 to Oregon Short Line 9500–9514
1930 10 UP-5 S-1701 68505–68514 Union Pacific 9078–9087
Total 88

Only one example has survived into preservation. Union Pacific 9000 which is the Prototype of the class, is preserved at the Railway and Locomotive Historical Society's museum at the Los Angeles County Fairplex in Pomona, California. It received a new boiler paint job in 2006-2007. Passengers can go inside the cab where they can blow 9000’s U.P. star brass 5 chime steam whistle (now air compressed.)

References[]