Union Pacific 2-8-8-0 "Consolidation Mallet" Type Locomotives

Class Details by Steve Llanso

Class MC series - simpled (Locobase 7467)

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

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 to all live steam. It's a bit unusual for the rebuild to shorten the stroke on the drivers, which the UP did in this program. Tractive effort is listed as 89,840 lb on the diagram, which shows no grate area because these were oil burners. 46 sq ft (4.3 sq m) of the firebox heating surface came in the form of arch tubes.

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

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 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.


Specifications by Steve Llanso
ClassMC series - simpledMC-2/MC-3/MC-4/MC-5MC-6
Locobase ID7467 7466 310
RailroadUnion Pacific (UP)Union Pacific (UP)Union Pacific (UP)
Whyte2-8-8-02-8-8-02-8-8-0
Road Numbers3500-35693600-36433645-3664
GaugeStdStdStd
BuildershopsAlcoAlco-Brooks
Year193719181924
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)87.89'87.04'87.04'
Axle Loading (Maximum Weight per Axle)57870 lbs59400 lbs
Weight on Drivers447023 lbs464730 lbs472000 lbs
Engine Weight501480 lbs495500 lbs502500 lbs
Tender Light Weight227280 lbs219000 lbs219000 lbs
Total Engine and Tender Weight728760 lbs714500 lbs721500 lbs
Tender Water Capacity12000 gals12000 gals12000 gals
Tender Fuel Capacity (oil/coal)5200 gals20 tons20 tons
Minimum weight of rail (calculated) on which locomotive could run93 lb/yard97 lb/yard98 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter57"57"57"
Boiler Pressure218 psi210 psi210 psi
High Pressure Cylinders (dia x stroke)23" x 30" (4)26" x 32" (2)26" x 32" (2)
Low Pressure Cylinders (dia x stroke)41" x 32" (2)41" x 32" (2)
Tractive Effort103183 lbs96627 lbs96627 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.33 4.81 4.88
Heating Ability
Firebox Area383 sq. ft383 sq. ft435.50 sq. ft
Grate Area88.20 sq. ft88.20 sq. ft88.20 sq. ft
Evaporative Heating Surface5622 sq. ft5668 sq. ft5412 sq. ft
Superheating Surface1320 sq. ft1320 sq. ft1320 sq. ft
Combined Heating Surface6942 sq. ft6988 sq. ft6732 sq. ft
Evaporative Heating Surface/Cylinder Volume194.85288.24275.22
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation192281852218522
Same as above plus superheater percentage228812204122226
Same as above but substitute firebox area for grate area9935895712109746
Power L11393779417943
Power MT549.87301.37296.80

Reference

Credits

Introduction and roster provided by Richard Duley. Class details and specifications provided by Steve Llanso of Sweat House Media.