Northern Pacific 2-10-0 "Decapod" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class M (Locobase 800)

Data from [] (19 June 2003) and from a 1944 Northern Pacific Locomotive Diagram book supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also DeGolyer, Volume 13, p. 121; and "Decapod Locomotives", Engineering (London), Volume 44 (29 July 1887), p. 117. Works numbers were 8168-8169 in August 1886.

Quoting a Northern Pacific "Tell Tale" article from its February 1950 issue, the site says that these two decapods were intended for heavy freight service in the Cascade mountains and were the heaviest locomotives in the world at the time they entered service.

Engineering reported that the pair had been "a surprise to the mechanical department of the system, owing to the unexpected ease with which they pass round the sharpest curve." This echoed a letter sent by the NP's Superintendent of Motive Power G W Cushing in January 1887 to Philadelphia, who wrote that the Ms could go "anywhere, either on bad track or curves, that an eight-wheeled engine could go." (reported in "Stampede Pass Switchback and Tunnel", Railroad Gazette, Volume 19 (23 December 1887), pp. 824-825.

At the time the NP was building switchbacks to work trains over the Cascades and the Ms would provide helper service. The Stampede tunnel, which would reduce maximum grades to 116 ft/mile (2.2%), was expected by the end of 1888.

The pair were later renumbered 1-2 and converted to yard switchers.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID800
RailroadNorthern Pacific (NP)
Number in Class2
Road Numbers500-501/1-2
Number Built2
BuilderBurnham, Parry, Williams & Co
Valve GearStephenson
Locomotive Length and Weight
Driver Wheelbase (ft / m)16.50 / 5.03
Engine Wheelbase (ft / m)24.33 / 7.42
Ratio of driving wheelbase to overall engine wheebase 0.68
Overall Wheelbase (engine & tender) (ft / m)49.17 / 14.99
Axle Loading (Maximum Weight per Axle) (lbs / kg)27,000 / 12,247
Weight on Drivers (lbs / kg)133,000 / 60,328
Engine Weight (lbs / kg)148,000 / 67,132
Tender Loaded Weight (lbs / kg)77,530 / 35,167
Total Engine and Tender Weight (lbs / kg)225,530 / 102,299
Tender Water Capacity (gals / ML)3500 / 13.26
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)7 / 6.40
Minimum weight of rail (calculated) (lb/yd / kg/m)44 / 22
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)46 / 1168
Boiler Pressure (psi / kPa)150 / 10.30
High Pressure Cylinders (dia x stroke) (in / mm)22" x 26" / 559x660
Tractive Effort (lbs / kg)34,880 / 15821.32
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.81
Heating Ability
Firebox Area (sq ft / m2)162 / 15.05
Grate Area (sq ft / m2)35.70 / 3.32
Evaporative Heating Surface (sq ft / m2)2310 / 214.60
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)2310 / 214.60
Evaporative Heating Surface/Cylinder Volume201.94
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation5355
Same as above plus superheater percentage5355
Same as above but substitute firebox area for grate area24,300
Power L13137
Power MT260.00

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Wes Barris