Union Pacific 4-12-2 Locomotives in the USA

Union Pacific 4-12-2

In the mid 1920s many western railroads were using the 2-10-2 "Santa Fe" type and 2-8-8-0 Consolidation Mallet type locomotives for mainline freight trains. These locomotives were getting the job done but were limited to about 20 mph. The Union Pacific Railroad experimented with a three-cylinder 4-10-2 "Overland" type in 1925 and actually bought ten of them. The 4-10-2 locomotives were capable of slightly greater speed while being capable of pulling about 20% more tonnage. The Union Pacific wanted more and approached the American Locomotive Company about a design for a 4-12-2. The locomotive would have more power and would ride better at higher speeds.

The Union Pacific Railroad ordered a single locomotive with a 4-12-2 wheel arrangement and the American Locomotive Company delivered it in March of 1926. This locomotive was the first locomotive built with this wheel arrangement and was given the name "Union Pacific" for the Railroad that first used this type of locomotive. It was designated as Class UP-1 and assigned road number 9000. It had 67" diameter drivers, three 27" diameter cylinders (two with 32" stroke and one with a 31' stroke), a 220 psi boiler pressure, it exerted 96,646 pounds of tractive effort and weighed 495,000 pounds. Later in 1926, fourteen more of these locomotives were delivered from ALCO and were designated as Class UP-2 and given road numbers 9001 through 9014. These locomotives were similar to number 9000.

In 1928, 1929 and 1930 a total of seventy-three more "Union Pacific" type locomotives were added to the UP roster. Class UP-3 included twenty-three locomotives, which were assigned road numbers 9015 through 9029 for those used on the UP and road numbers 9055 through 9062 were assigned to the eight locomotives that were used on the OWR&N. Twenty-five locomotives were designated as Class UP-4 and were assigned road numbers 9030 through 9054. The last group of twenty-five was designated as Class UP-5 and included 9078 through 9087 for those locomotives used on the UP and numbers 9500 through 9514 for the fifteen that were used on the OSL.

The American Locomotive Company built all eighty-eight of these fast freight locomotives for the Union Pacific Railroad. They were three-cylinder locomotives with the third cylinder located in the center of the steam chest. The third cylinder drove an eccentric in the axel of the second pair of drivers. The fourth set of drivers were flangeless, but it was later determined that this was not necessary and a small flange was added to these drivers. They were built to the same basic specifications as its first delivered "Union Pacific" type locomotive, number 9000. The UP ran the 4-12-2 "Union Pacific" locomotives at 50 mph hauling 120 car trains.

There is one surviving UP 4-12-2 "Union Pacific" type locomotive. It is number 9000 displayed at the Los Angeles County Fairplex in Pomona, CA


ClassQty.UP NumbersRoadRoad NumbersYear BuiltBuilderNotes
UP-1 19000UP90001926ALCO1
UP-3 89055-9062OWR&N9700-97071928ALCO5
  1. Number 9000 was retired in 1956. It is preserved and is located in Pomona, CA.
  2. Number 9004 was sold to OWRR&N in September 1928; renumbered to OWRR&N 9708; sold back to UP in September 1929; renumbered back to UP 9004. Numbers 9001-9014 scrapped as follows: 9002 & 9008 in 1952, 9004, 9005 & 9012 in 1954, 9001, 9003, 9006, 9009, 9010, 90011, 9013 & 9014 in 1955 and 9007 in 1956.
  3. Number 9018 wrecked due to boiler explosion on October 20, 1948 at Upland, KS. Numbers9015-9029 scrapped as follows: 9018 in 1948, 9025 in 1953, 9019, 9020, 9021, 9022, 9023, 9024, 9027, 9028 & 9029 in 1954, 9015, 9016 & 9017 in 1955 and 9026 in 1956.
  4. Numbers 9030-9054 scrapped as follows: 9034 in 1953, 9030,.9032, 9036, 9039, 9045, 9047, 9049, 9053 & 9054 in 1954, 9031, 9033, 9035, 9037, 9038, 9041, 9042, 9043, 9044, 9046, 9048, 9050 & 9051 and 9040 & 9052 in 1956.
  5. Numbers 9055-9062 were built as OWRR&N numbers 9700-9707 in 1928; sold to UP in September 1929; renumbered to UP numbers 9055-9062. Numbers 9055-9062 scrapped as follows: 9056 in 1953, 9055, 9057 & 9059 in 1954, 9061 in 1955 and 9058, 9060 & 9062 in 1956.
  6. Numbers 9500-9514 were ordered as UP 9063-9077; delivered as OSL 9500-9514. Numbers 9500-9514 scrapped as follows: 9504, 9506, 9507, 9511, 9513 & 9514 in 1954, 9502, 9503, 9508, 9509, 9510 &9512 in 1955 and 9500, 9501 & 9505 in 1956.
  7. Numbers 9078-9087 scrapped as follows: 9081 in 1953, 9079, 9080, 9083 & 9087 in 1954 and 9078, 9082, 9084, 9085 & 9086 in 1955.

Class Details by Steve Llanso of Sweat House Media

Class UP-1 to UP-5 (Locobase 290)

Data from UP 10-1936 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also Alfred W Bruce,The Steam Locomotive in America - Its development in the twentieth century (New York: W W Norton, 1952), pp 302-303). (Thanks to Chris Hohl for his 9 May 2015 email commenting on tender weights and capacities.) Brooks works numbers were 66544 in March 1926, 67024-67034 in August, 67035-67037 in September, 67581-67584 in June 1928, 67585-67595 in July. Schenectady followed with works numbers 67596-67603 in July 1928, 67944-67949 in 1929 (month undetermined), 67950-67968 in July 1929, 68490-68504 in July 1930, 68505-68514 in August 1930. (NB: With the exception of two Mikado tanks for logging service and a snowplow, these were the last locomotives turned out at Brooks' Dunkirk Works.

Valve motion had limited cutoff. The firebox's enormous heating surface included 62 sq ft (5.76 sq m) of arch tubes and a long combustion chamber. observed that part of that combustion chamber was created by a low wall placed just behind the last driving axle. Thus the effective grate was reduced, but overall direct heating service was preserved. Further thermal encouragement took the form of a Worthington 5-S feed water heater.

The two outside cylinders had 32-in strokes; the inside cylinder was driven by Gresley conjugated gear and had a 31-in stroke. Notice the very rare instance of identical tube and flue diameters. Although the center motion gave some maintenance problems and the fixed wheelbase was the longest ever mounted, these "Union Pacifics" were considered a great success.

Bruce notes with satisfaction that the locomotives had been delivered as "slow-speed units" with a restriction of 35-mph. "However," Bruce comments,"because of the long wheelbase the engines were very stable riding [sic], and speeds of 60 mph or over were very frequently reported." They also handled 2 % grades and 6-8 degree curves despite their extreme length.

No other railroads built such long-wheelbase engines, however. Another unusual note about this class was that the highest axle loading was found on the trailing truck under the firebox and not one of the driving axles.

Note on the cylinder and valve gear layout: Based on correspondence with John E Bush and examination of photos in the latter's book, Wes Barris (http://www.steamlocomotive.com/3cylinder/, viewed 30 March 2004) has concluded that the first axle was in fact not cranked. Instead, the spacing between the first two axles was 18" greater than was true of the other four. He notes that Barry Koeb, an R&LHS member responsible for the UP 9000 has been inside that engine's frame and saw no crank.

"The Cowboy" (permstev@cableone.net as of 30 March 2004) creates new files for the virtual railroad simulator Trainz Railroad Simulator 2004. In his notes on the UP 9000 series he adds quite a bit of additional information. The center cylinder and piston rod were raked at 8 degrees above the horizontal to clear the first axle. He adds: "This inclination resulted in a uneven positioning of the intervals for the 3 cylinders. When looking at the locomotive from the right side, the intervals are as follows rotating in a clockwise manner: 112 Degrees to the middle pin, then 128 Degrees to the left pin finally 120 degrees back to the right pin. This positioning gave the locomotive a very distinctive and uneven sounding exhaust."

TheCowboy says that the friction bearings in the Gresley gear wore quickly and that 8 of the class were converted to a "third-link" motion layout in which a second Walschaert gear was added to the right side. This additional link transmitted motion to the inside cylinder through a rocker arm. Later 9000s had roller bearings on their Gresley gear and were not so modified.

He also notes that the air compressors on the early 9000s, whose smokebox location gave the class such a distinctive look, were easier to maintain when they were moved to the sides of the boiler. The result gave rise to the name "Bald-Faced Nines".

Brooks's first set of tenders, built in March 1926, was equipped with an Elvin stoker, carried 15,000 US gallons (56,775 litres) of water and 21 tons (19.1 metric tons) of coal. Light weight came to 122,500 lb (55,565 kg), loaded weight reached 287,000 lb (130,181 kg). The basic structure remained unchanged in the later tenders, which had Duplex stokers, but loaded weight and capacity increased to the levels shown in the specs.

Principal Dimensions by Steve Llanso of Sweat House Media
ClassUP-1 to UP-5
Locobase ID290
RailroadUnion Pacific (UP)
Number in Class88
Road Numbers9000-9087
Number Built88
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)30.66 / 9.35
Engine Wheelbase (ft / m)52.33 / 15.95
Ratio of driving wheelbase to overall engine wheebase 0.59
Overall Wheelbase (engine & tender) (ft / m)91.50 / 27.89
Axle Loading (Maximum Weight per Axle) (lbs / kg)60,000 / 27,216
Weight on Drivers (lbs / kg)354,000 / 160,572
Engine Weight (lbs / kg)496,500 / 225,209
Tender Loaded Weight (lbs / kg)310,599 / 140,886
Total Engine and Tender Weight (lbs / kg)807,099 / 366,095
Tender Water Capacity (gals / ML)18,000 / 68.18
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)22 / 20
Minimum weight of rail (calculated) (lb/yd / kg/m)98 / 49
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)67 / 1702
Boiler Pressure (psi / kPa)220 / 15.20
High Pressure Cylinders (dia x stroke) (in / mm)27" x 32" / 686x813
Low Pressure Cylinders (dia x stroke) (in / mm)27" x 31" / 686x787 (1)
Tractive Effort (lbs / kg)96,646 / 43837.94
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.66
Heating Ability
Firebox Area (sq ft / m2)591 / 54.93
Grate Area (sq ft / m2)108.25 / 10.06
Evaporative Heating Surface (sq ft / m2)5853 / 543.96
Superheating Surface (sq ft / m2)2560 / 237.92
Combined Heating Surface (sq ft / m2)8413 / 781.88
Evaporative Heating Surface/Cylinder Volume276.01
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation23,815
Same as above plus superheater percentage30,960
Same as above but substitute firebox area for grate area169,026
Power L124,856
Power MT928.78

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Wes Barris