Union Pacific 2-8-8-0 Locomotives of the USA


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Class Details by Steve Llanso of Sweat House Media

Class MC-2/MC-3/MC-4/MC-5 (Locobase 7466)

Data from UP 10 - 1936 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.

This low-drivered design was the first of a series of pusher freight compounds that by 1929 were running between Cheyenne and Laramie, between Ogden and Green River, between La Grande and Rieth and between Pocatello and Granger.

In addition to the Union Pacific's 15, the Oregon Short Lines took the last engine of the Schenectady batch of MC-2s (works numbers were 58262-58277 in May 1918.)

The MC-2s were followed in 1920 by 19 Brooks-built engines MC-3 of similar dimensions and greater weight (works numbers were 61905-61922 in July 1920 and 61923 in September.)

Like the MC-2s, these had 15" (381 mm) piston valves on all four cylinders

Brooks added 10 more MC-4s in 1923 along identical lines (63771-63780 in March 1923): five for the UP, two for the Oregon Short Line, and three for the Oregon Washington Railroad & Navigation

The last batch of MC-5s were delivered five months later (works numbers 64402-64406 in August 1923).

Class MC-6 (Locobase 310)

Data from tables in 1930 Locomotive Cyclopedia and UP 10 - 1936 Locomotive Diagrams supplied in May 2005 by Allen Stanley. Additional information from Gordon McCulloh via September 2012 email. Works numbers were 65665-65683 in June 1924, 65684 in July.

This last batch of Mallet Consolidations had twenty fewer tubes in the boiler than any of the earlier batches (for the latter, see Locobase 7466). The firebox heating surface area had 97.5 sq ft (9.05 sq m) of thermic syphons. Like the earlier engines, this class handled helper duties in Wyoming, running between Cheyenne and Laramie, between Ogden and Green River, between La Grande and Rieth and between Pocatello and Granger.

See Locobase 7467 for the simple-expansion conversion applied to all of these Mallets.

Class SA-C-2 to SA-C-6 (Locobase 7467)

Data from UP 10 - 1936 and UP 11 - 1946 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. (Thanks to Chris Hohl for his 18 June 2015 email giving the proper class ID.

All 70 compound Mallets built to the same wheel arrangement (Locobases 7466 and 310) were obviously very satisfactory pusher locomotives for the Union Pacific. In 1937, the railroad decided to modify the cylinder layout--and the class ID, as Chris Hohl points out--to Simple Articulated-Consolidation. When replacing the compound setup with four simple-expansion cylinders, the UP took the unusual step of shortening the stroke. Slightly taller drivers and piston valves on all cylinders completed the rebuild.

46 sq ft (4.3 sq m) of the firebox heating surface came in the form of arch tubes; acombustion chamber contributed an additional amount (not found in the diagrams) . All had feed water heaters; Coffins went into 3520-3530, 3533, and 3538 while the others received Worthingtons. 3556 was equipped with thermic syphons.

The 70 locomotives were converted in 1937-1943. Some of the conversions operated until 1954.

Specifications by Steve Llanso of Sweat House Media
ClassMC-2/MC-3/MC-4/MC-5MC-6SA-C-2 to SA-C-6
Locobase ID7466 310 7467
RailroadUnion Pacific (UP)Union Pacific (UP)Union Pacific (UP)
Number in Class452070
Road Numbers3600-36433645-36643500-3569
Number Built1620
Valve GearWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase15.50'15.50'15.50'
Engine Wheelbase50.50'50.50'50.50'
Ratio of driving wheelbase to overall engine wheebase 0.31 0.31 0.31
Overall Wheelbase (engine & tender)87.04'87.04'87.89'
Axle Loading (Maximum Weight per Axle)57870 lbs59400 lbs
Weight on Drivers464730 lbs472000 lbs470480 lbs
Engine Weight495500 lbs502500 lbs501480 lbs
Tender Light Weight219000 lbs219000 lbs227280 lbs
Total Engine and Tender Weight714500 lbs721500 lbs728760 lbs
Tender Water Capacity12000 gals12000 gals12000 gals
Tender Fuel Capacity (oil/coal)20 tons20 tons5200 gals
Minimum weight of rail (calculated)97 lb/yard98 lb/yard98 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter57"57"59"
Boiler Pressure210 psi210 psi218 psi
High Pressure Cylinders (dia x stroke)26" x 32"26" x 32"23" x 30"
Low Pressure Cylinders (dia x stroke)41" x 32" (2)41" x 32" (2)
Tractive Effort96627 lbs96627 lbs99685 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.81 4.88 4.72
Heating Ability
Firebox Area383 sq. ft435.50 sq. ft383 sq. ft
Grate Area88.20 sq. ft88.20 sq. ft88.20 sq. ft
Evaporative Heating Surface5668 sq. ft5412 sq. ft5622 sq. ft
Superheating Surface1320 sq. ft1320 sq. ft1320 sq. ft
Combined Heating Surface6988 sq. ft6732 sq. ft6942 sq. ft
Evaporative Heating Surface/Cylinder Volume288.24275.22194.85
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation185221852219228
Same as above plus superheater percentage220412222622881
Same as above but substitute firebox area for grate area9571210974699358
Power L17941794314426
Power MT301.37296.80540.79


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