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


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)
CountryUSAUSAUSA
Whyte2-8-8-02-8-8-02-8-8-0
Number in Class452070
Road Numbers3600-36433645-36643500-3569
GaugeStdStdStd
Number Built1620
BuilderAlcoAlco-Brooksshops
Year191819241942
Valve GearWalschaertWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft)15.5015.5015.50
Engine Wheelbase (ft)50.5050.5050.50
Ratio of driving wheelbase to overall engine wheebase 0.31 0.31 0.31
Overall Wheelbase (engine & tender) (ft)87.0487.0487.89
Axle Loading (Maximum Weight per Axle) (lbs)57,87059,400
Weight on Drivers (lbs)464,730472,000470,480
Engine Weight (lbs)495,500502,500501,480
Tender Loaded Weight (lbs)219,000219,000227,280
Total Engine and Tender Weight (lbs)714,500721,500728,760
Tender Water Capacity (gals)12,00012,00012,000
Tender Fuel Capacity (oil/coal) (gals/tons)20205200
Minimum weight of rail (calculated) (lb/yd)979898
Geometry Relating to Tractive Effort
Driver Diameter (in)575759
Boiler Pressure (psi)210210218
High Pressure Cylinders (dia x stroke) (in)26" x 32"26" x 32"23" x 30" (4)
Low Pressure Cylinders (dia x stroke) (in)41" x 32"41" x 32"
Tractive Effort (lbs)96,62796,62799,685
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.81 4.88 4.72
Heating Ability
Firebox Area (sq ft)383435.50383
Grate Area (sq ft)88.2088.2088.20
Evaporative Heating Surface (sq ft)566854125622
Superheating Surface (sq ft)132013201320
Combined Heating Surface (sq ft)698867326942
Evaporative Heating Surface/Cylinder Volume288.24275.22194.85
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation18,52218,52219,228
Same as above plus superheater percentage22,04122,22622,881
Same as above but substitute firebox area for grate area95,712109,74699,358
Power L17941794314,426
Power MT301.37296.80540.79

Reference


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