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.
|Class||Road Numbers||Year Built||Builder|
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 (60 kph) 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: " 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 ([external link], 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 ([external link], 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.
|Principal Dimensions by Steve Llanso of Sweat House Media|
|Railroad||Union Pacific (UP)|
|Number in Class||65|
|Road Numbers||7000-7039, 7850-69|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)||19.60 / 5.97|
|Engine Wheelbase (ft / m)||41.25 / 12.57|
|Ratio of driving wheelbase to overall engine wheebase||0.48|
|Overall Wheelbase (engine & tender) (ft / m)|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)||58,290 / 26,440|
|Weight on Drivers (lbs / kg)||233,060 / 105,714|
|Engine Weight (lbs / kg)||350,250 / 158,871|
|Tender Loaded Weight (lbs / kg)||237,500 / 107,728|
|Total Engine and Tender Weight (lbs / kg)||587,750 / 266,599|
|Tender Water Capacity (gals / ML)||12,000 / 45.45|
|Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)||20 / 18.20|
|Minimum weight of rail (calculated) (lb/yd / kg/m)||97 / 48.50|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||73 / 1854|
|Boiler Pressure (psi / kPa)||200 / 13.80|
|High Pressure Cylinders (dia x stroke) (in / mm)||29" x 28" / 737x711|
|Tractive Effort (lbs / kg)||54,838 / 24874.13|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.25|
|Firebox Area (sq ft / m2)||382 / 35.49|
|Grate Area (sq ft / m2)||84 / 7.80|
|Evaporative Heating Surface (sq ft / m2)||4974 / 462.10|
|Superheating Surface (sq ft / m2)||1242 / 115.38|
|Combined Heating Surface (sq ft / m2)||6216 / 577.48|
|Evaporative Heating Surface/Cylinder Volume||232.37|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||16,800|
|Same as above plus superheater percentage||20,160|
|Same as above but substitute firebox area for grate area||91,680|