Union Pacific 4-8-2 "Mountain" Type Locomotives

Introduction

The Union Pacific Railroad took delivery of forty 4-8-2s (road numbers 7000 through 7039) from the American Locomotive Company in 1922. These Class MT-1 "Mountains" had 29 x 28 cylinders, 73" drivers, a boiler pressure of 200 psi, a tractive effort of 54,838 lbs and each weighed 348,000 pounds. A year later, fifteen more (road numbers 7850 through 7864) were added to the roster. These last fifteen, ALCO built, Class MT-1s were similar to the ones delivered in 1922 except they weighed 345,000 pounds.

In 1924, five more "Mountains" came from ALCO. These locomotives were designated as Class MT-2 and were assigned road numbers 7865 through 7869. They were oil burners and had 29 x 28 cylinders, 73" drivers, a boiler pressure of 200 psi which resulted in a tractive effort of 54,838 pounds. The combined weight of the Class MT-2 locomotive and its tender was 634,740 lbs with a full load of 15,000 gallons of water and 5,480 gallons of oil.

All of the Union Pacific "Mountains" were scrapped by 1956.

Roster by Richard Duley

ClassRoad NumbersYear BuiltBuilder
MT-17000-70391922ALCO
MT-17850-78641923ALCO
MT-27865-78691924ALCO

Class Details by Steve Llanso

Class MT-1/MT-2 (Locobase 230)

Data from 1936 Union Pacific locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive collection. See also DeGolyer, Vol 69, pp. 147+; Railway Journal, Volume 28, No 7 (July 1922), pp. 14-15, "Boiler of Union Pacific Mountain Type Locomotive," Boiler Maker August 1922), pp. 217-222; and "A New Mountain for the Union Pacific," Railway Age, Volume 72, No 23 (10 June 1922), pp. 1325-1329. See Locobase 6082 for a full description of the Young valve gear. Locobase thanks Gordon McCulloh for his 3 Feb 2012 email asking about the TTTs, which induced a rewrite of several entries.

These were the only Mountains the Union Pacific ran. When RJ's July 1922 issue featured this greyhound, the author commented on the "lightness of parts" that went into the design. He noted that the 2-8-2s then in service were not equal to the task of maintaining an average speed of 37 mph over the 484 miles between Ogden, Utah and Cheyenne, Wyoming; their drivers were simply too small to meet the higher speed requirements.

In addition, the author said, "It may not be generally known that there are grades west of Cheyenne in the Wyoming division of long distances running as high as 1.55 per cent on the westbound, and 1.14 per cent grades on the eastbound operation. Six through passenger trains pass over this region daily"

Then RJ's reporter noted the catch in using a 4-8-2 layout with taller drivers: "The only difficulty in introducing the mountain type of locomotive was in the recognized fact that the weight should not exceed 345.000 Ibs., for while the railroad, as is well known, is double tracked and of the most substantial construction, the numerous bridges, viaducts and other structures are not calculated to meet the requirements of heavier motive power than the weight referred to."

The result was a success: "[7000] has not been approached in point of design where boiler capacity in relation to weight is considered, and has only been made possible by a close comparison with other types where weights are known and by thorough tests of individual parts and material in order to ascertain what was possible as the looked for accomplishment, looking towards a general introduction of the mountain type of locomotive, if the success of the experiment should prove beyond controversy."

Firebox heating surface included 33.5 sq ft (3.1 sq m) of arch tubes as well as the surface area of the combustion chamber.

RJ also commented on the choice of Young valve gear for these big engines: "Mechanical officials of the Union Pacific Railroad are also placing considerable dependence on the Young valve gear as a means for increasing capacity of this locomotive on hard pulls. The ability of the Young valve gear to give a high mean effective cylinder pressure due indirectly to its long travel, is well known. In full gear, the valves on this locomotive, which are 14 inches in diameter, have a travel of 9 in." (9 inches of valve travel was indeed long for that day or any other steam era.)

A Trainorders forum thread headed UP Steam Question and started by "yardclerk" included a 6 December 2006 entry, time-stamped 4:32 AM (http://www.trainorders.com/discussion/read.php?10,1299181, last accessed 8 February 2012) in which "4-12-2" added this interesting tidbit: "By the time Union Pacific ordered the first of their 4-8-2's for 1922 delivery the Young gear was being marketed by Pyle-National, a company most think was involved strictly in electric appliances. I remember my surprise when I first learned this. I don't know if this was P-N's only venture into the marketing of locomotive appliances outside their huge array of electrical products, but I do believe it represented a major departure for P-N and I think speaks volumes about the promise held in the Young design, otherwise I don't believe P-N would have "taken the chance" on this product."

The RJ reporter noted also the steam-passage design: "Morever, as will be noted from the drawings, the steam passages in the cylinders are amply proportioned, being cored in accordance with the Cole patent."

In the 1930s, the class was modified with Walschaert valve gear and one-piece cast-steel frames. Locomotives 7850-7864 were leased to the Los Angeles & Salt Lake.

The diagrams show that many were later fitted with a streamliner casing and bullet nosecap. They also reveal the 16" piston valves that went in at that time. Wes Barris's steamlocomotive.com site (http://www.steamlocomotive.com/colored/#brown, last accessed 27 February 2010 ) shows a more extensive streamlining of 7002. The purpose of streamlining 7002 (and Pacific 2906, described in Locobase 6612) was to substitute for the early diesels when they were unable to pull the heavy, all-Pullman Forty-Niner trains 5 times a month between Chicago and San Francisco in 1938-1941 to help celebrate the Golden Gate Exposition. Like the 2906, the UP fitted Timken roller bearings on every engine axle and in the rods as well. Weight grew to 257,500 lb on the drivers and 382,500 lb for the engine overall.

Like that of the 2906, the casing adopted fell short of aesthetic triumph to perhaps a greater degree than the installation on the 2906. The most dominant color was chocolate brown (called Leaf Brown by the UP), accented by the Armour Yellow stripe on the bluntly curved nose (it had yellow whiskers as well), Scarlet trim above yellow on the valences that underlay the running boards, lazy-oval cab windows, and the trademark yellow-with-red stripe tender. The overall effect was to reduce the mighty Mountain and its 6-axle tender to a Lionel nightmare.


Specifications by Steve Llanso
ClassMT-1/MT-2
Locobase ID230
RailroadUnion Pacific (UP)
CountryUSA
Whyte4-8-2
Road Numbers7000-7039, 7850-69
GaugeStd
BuilderAlco-Brooks
Year1922
Valve GearYoung
Locomotive Length and Weight
Driver Wheelbase19.60'
Engine Wheelbase41.25'
Ratio of driving wheelbase to overall engine wheebase 0.48
Overall Wheelbase (engine & tender)
Axle Loading (Maximum Weight per Axle)58290 lbs
Weight on Drivers233060 lbs
Engine Weight350250 lbs
Tender Light Weight237500 lbs
Total Engine and Tender Weight587750 lbs
Tender Water Capacity12000 gals
Tender Fuel Capacity (oil/coal)20 tons
Minimum weight of rail (calculated) on which locomotive could run97 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter73"
Boiler Pressure200 psi
Cylinders (dia x stroke)29" x 28"
Tractive Effort54838 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.25
Heating Ability
Firebox Area382 sq. ft
Grate Area84 sq. ft
Evaporative Heating Surface4974 sq. ft
Superheating Surface1242 sq. ft
Combined Heating Surface6216 sq. ft
Evaporative Heating Surface/Cylinder Volume232.37
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation16800
Same as above plus superheater percentage20160
Same as above but substitute firebox area for grate area91680
Power L120532
Power MT776.89

Photos

Reference

Credits

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