Uintah Railway 2-6-6-2 "Mallet Mogul" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class 50 (Locobase 3568)

Data from Wiener (1930) and DeGolyer, Volume 77, pp. 282+. See also Uintah 50 and 51 Locomotive Project,", Republic Locomotive Works at [], accessed 18 December 2016.(Thanks to Chris Hohl for his 2 February 2023 email correcting water capacity, adding the 51's higher weights Works numbers were 59261 in June 1926; 60470 emerged almost two years later in May 1928.

This pocket rocket was built for a mountain narrow-gauge that operated in Western Colorado and Utah. The long water tanks extended from the cab to the middle of the front engine unit. Steam was led forward under the boiler jacket in a dry pipe to the superheater as usual, but returned for the rear cylinders in two heavily lagged external pipes that branched around the stack and dropped down to the cylinders behind the water tanks on each side. The cylinders were supplied by 8" (203 mm) piston valves with 5" (127 mm) travel.

Chris Hohl reported weight differences between the two locomotives. The Locobase data refer to the 50. The 51 put 200,400 lb (90,900 kg) on the drivers and 244,400 lb (110,858 kg) on all axles.

The leading truck was equalized with the front unit's drivers and could swing 6 3/4" (171 mm) to each side. The rear, bissell truck was equalized with the rear driving set.

These Mallet Prairie Tanks could handle twice the train load on the 5% grade that ruled, wrangling 240 tons (218 tonnes) up such a slope. On the 1.1% grade between Watson and Dragon, 51 was rated at 1,150 tons (1,045 tonnes). At the other extreme, the 7.5% grade between Atehea and Baxter Pass brought the tonnage rating down to 145 tons (131.8 tonnes).

Bill Pratt ([], accessed 9 Jan 2006 and at the time recommended as an excellent site covering the Uintah Railroad past and present; alas apparently no longer active), notes that as delivered the 50 had one steam dome in the middle of the boiler. After an engineer negotiating the five miles of 7 1/2% adverse grade realized the water glass was showing empty, a second steam dome was installed near the cab.

[] notes that the Uintah sold off both locomotives in 1940 to Sumpter Valley in Oregon, where they operated until 1947 as 250 & 251. Still yoked in their joint destiny, the two engines then went to the International Railways of Central America in Escuintla, Guatemala. 251 retired first in 1962 and 250 followed in 1964.

Principal Dimensions by Steve Llanso of Sweat House Media

Locobase ID3568
RailroadUintah Railway
Number in Class2
Road Numbers50-51
Number Built2
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)15.34 / 4.68
Engine Wheelbase (ft / m)38.25 / 11.66
Ratio of driving wheelbase to overall engine wheelbase 0.40
Overall Wheelbase (engine & tender) (ft / m)38.25 / 11.66
Axle Loading (Maximum Weight per Axle) (lbs / kg)30,240 / 13,717
Weight on Drivers (lbs / kg)194,000 / 87,997
Engine Weight (lbs / kg)236,300 / 107,184
Tender Loaded Weight (lbs / kg)
Total Engine and Tender Weight (lbs / kg)236,300
Tender Water Capacity (gals / ML)2800 / 9.85
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT) 4.50 / 4
Minimum weight of rail (calculated) (lb/yd / kg/m)54 / 27
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)42 / 1067
Boiler Pressure (psi / kPa)210 / 14.50
High Pressure Cylinders (dia x stroke) (in / mm)15" x 22" / 381x559 (4)
Tractive Effort (lbs / kg)42,075 / 19084.92
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.61
Heating Ability
Tubes (number - dia) (in / mm)146 - 2" / 51
Flues (number - dia) (in / mm)24 - 5.375" / 137
Flue/Tube length (ft / m)18 / 5.49
Firebox Area (sq ft / m2)125 / 11.61
Grate Area (sq ft / m2)37.40 / 3.48
Evaporative Heating Surface (sq ft / m2)2100 / 195.17
Superheating Surface (sq ft / m2)505 / 46.93
Combined Heating Surface (sq ft / m2)2605 / 242.10
Evaporative Heating Surface/Cylinder Volume233.33
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation7854
Same as above plus superheater percentage9346
Same as above but substitute firebox area for grate area31,238
Power L111,874
Power MT809.62

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