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).
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.
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.
|Principal Dimensions by Steve Llanso of Sweat House Media|
|Class||MC-2/MC-3/MC-4/MC-5||MC-6||SA-C-2 to SA-C-6|
|Railroad||Union Pacific (UP)||Union Pacific (UP)||Union Pacific (UP)|
|Number in Class||45||20||70|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)||15.50 / 4.72||15.50 / 4.72||15.50 / 4.72|
|Engine Wheelbase (ft / m)||50.50 / 15.39||50.50 / 15.39||50.50 / 15.39|
|Ratio of driving wheelbase to overall engine wheebase||0.31||0.31||0.31|
|Overall Wheelbase (engine & tender) (ft / m)||87.04 / 26.53||87.04 / 26.53||87.89 / 26.79|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)||57,870 / 26,249||59,400 / 26,943|
|Weight on Drivers (lbs / kg)||464,730 / 210,798||472,000 / 214,096||470,480 / 213,406|
|Engine Weight (lbs / kg)||495,500 / 224,755||502,500 / 227,930||501,480 / 227,468|
|Tender Loaded Weight (lbs / kg)||219,000 / 99,337||219,000 / 99,337||227,280 / 103,093|
|Total Engine and Tender Weight (lbs / kg)||714,500 / 324,092||721,500 / 327,267||728,760 / 330,561|
|Tender Water Capacity (gals / ML)||12,000 / 45.45||12,000 / 45.45||12,000 / 45.45|
|Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)||20 / 18.20||20 / 18.20||5200 / 19.70|
|Minimum weight of rail (calculated) (lb/yd / kg/m)||97 / 48.50||98 / 49||98 / 49|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||57 / 1448||57 / 1448||59 / 1448|
|Boiler Pressure (psi / kPa)||210 / 14.50||210 / 14.50||218 / 15|
|High Pressure Cylinders (dia x stroke) (in / mm)||26" x 32" / 660x813||26" x 32" / 660x813||23" x 30" / 584x762 (4)|
|Low Pressure Cylinders (dia x stroke) (in / mm)||41" x 32" / 1041x813||41" x 32" / 1041x813|
|Tractive Effort (lbs / kg)||96,627 / 43829.32||96,627 / 43829.32||99,685 / 45216.41|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.81||4.88||4.72|
|Firebox Area (sq ft / m2)||383 / 35.59||435.50 / 40.46||383 / 35.58|
|Grate Area (sq ft / m2)||88.20 / 8.20||88.20 / 8.19||88.20 / 8.19|
|Evaporative Heating Surface (sq ft / m2)||5668 / 526.77||5412 / 502.79||5622 / 522.30|
|Superheating Surface (sq ft / m2)||1320 / 122.68||1320 / 122.63||1320 / 122.63|
|Combined Heating Surface (sq ft / m2)||6988 / 649.45||6732 / 625.42||6942 / 644.93|
|Evaporative Heating Surface/Cylinder Volume||288.24||275.22||194.85|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||18,522||18,522||19,228|
|Same as above plus superheater percentage||22,041||22,226||22,881|
|Same as above but substitute firebox area for grate area||95,712||109,746||99,358|