Union Pacific 2-8-8-0 "Consolidation Mallet" Locomotives in the USA

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

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

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).

Locobase 7467 describes the four-cylinder conversions to simple expansion in the late 1930s.

Class MC-4 (Locobase 16520)

Data from UP 10 - 1936 Locomotive Diagrams and ORR&WCo 1 - 1936 supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange; and "Order No. B-1583 - March 1923", Class 2880 C S 495, American Locomotive Company builder's card supplied by Larry Walton in his 15 December 2020 email. (Locobase thanks Larry for sending it along.)

Continuing the stocking of low-drivered compound superheated Mallets described in Locobases 7466 and 310, Alco's Brooks works in Dunkirk, NY 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 (3704-3705), and three for the Oregon Washington Railroad & Navigation (3803-3805). These had tweaks to the dimensions, but were otherwise repeats of the earlier design.

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 Rail Data Exchange. (Thanks to Chris Hohl for his 18 June 2015 email giving the proper class ID. Thanks too to Bernhard Schroeter for his 3 April 2018 email correcting the English-to-metric conversion of the driver diameter.)

All 70 compound Mallets built to the same wheel arrangement (Locobases 7466, 310, 16520) 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; a combustion 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.