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.
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 1 engine of the Schenectady batch of MC-2s. These were followed in 1920 by 19 Brooks-built engines MC-3 of similar dimensions and greater weight; like the MC-2s, these had 15" (381 mm) piston valves on all four cylinders Brooks added 5 more MC-4s in 1922 along identical lines; Oregon Short Lines took delivery of 2 in 1923 and the OWR&N took 3. In 1923, Brooks added another 5 as MC-5s.
The last batch, delivered a year later, had a reduced tube count; see Locobase 310.
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|
|Class||MC series - simpled||MC-2/MC-3/MC-4/MC-5||MC-6|
|Railroad||Union Pacific (UP)||Union Pacific (UP)||Union Pacific (UP)|
|Locomotive Length and Weight|
|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 lbs||59400 lbs|
|Weight on Drivers||447023 lbs||464730 lbs||472000 lbs|
|Engine Weight||501480 lbs||495500 lbs||502500 lbs|
|Tender Light Weight||227280 lbs||219000 lbs||219000 lbs|
|Total Engine and Tender Weight||728760 lbs||714500 lbs||721500 lbs|
|Tender Water Capacity||12000 gals||12000 gals||12000 gals|
|Tender Fuel Capacity (oil/coal)||5200 gals||20 tons||20 tons|
|Minimum weight of rail (calculated) on which locomotive could run||93 lb/yard||97 lb/yard||98 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||218 psi||210 psi||210 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 Effort||103183 lbs||96627 lbs||96627 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.33||4.81||4.88|
|Firebox Area||383 sq. ft||383 sq. ft||435.50 sq. ft|
|Grate Area||88.20 sq. ft||88.20 sq. ft||88.20 sq. ft|
|Evaporative Heating Surface||5622 sq. ft||5668 sq. ft||5412 sq. ft|
|Superheating Surface||1320 sq. ft||1320 sq. ft||1320 sq. ft|
|Combined Heating Surface||6942 sq. ft||6988 sq. ft||6732 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||194.85||288.24||275.22|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||19228||18522||18522|
|Same as above plus superheater percentage||22881||22041||22226|
|Same as above but substitute firebox area for grate area||99358||95712||109746|