Northern Pacific 2-6-2 "Prairie" Locomotives in the USA


Class Details by Steve Llanso of Sweat House Media

Class T (Locobase 817)

Data from table in June 1907 American Engineer and Railroad Journal and from "'Prairie' Type Locomotive, Northern Pacific Ry," The Locomotive Magazine, Vol XII (15 December 1906), pp. 212-213. See also "Locomotive Boilers with Combustion Chambers", Engineering News, Volume LVI, No 21 (22 November 1906), pp. 531-534; and Northern Pacific Form 7310 Locomotive Cards supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection. Works numbers were 39508-39511 in May 1906, 39512-39527 in June, 40135-40150 in August, 40151-40164 in September, 40878-40888 in November, 40889-40905 in December.

40906-40907 in January 1907, 41924-41933 in February, 41934-41945 in March, 41946-41963 in April, 42235-42260 in May, and 42261-42264 in June.

Procured for light freight service in a wheel arrangement that was a first for the NP. They were among 70 engines procured by the NP that year with combustion chambers. David Van Alstyne, the NP's mechanical superintendent, installed a combustion chamber in T-class engine 2378. He said that the principal reason for doing so was to reduce leakage in tubes (especially in regions of bad water) caused by direct contact with the firebox's fire. Van Alstyne reported that the test had borne out his hopes. The brick arch was in place and the tubes showed little sign of stress or leakage. In his report to the Northwest Railway Club, he added: "What seems to me an especially good feature is ...that it very materially increases the heating surface of the firebox."

Firebox heating surface area included a lone arch tube contributing 9 sq ft (0.83 sq m).

Locobase wonders if it was used to stabilize the arch.

Six were later converted to light Mikados as the W-4s. Ten more were modified as T-1s; see Locobase 918.


Class T-1 - superheated (Locobase 818)

Data from NP Locomotive Data Cards in August 2013 by Allen Stanley from his extensive Rail Data Exchange Collection.

Modified from Ts (Locobase 817) in the 1920s. The update was confined to adding a superheater (although the engineer did get a power reverse). The engines retained their 12" (305 mm) piston valves, but cylinder diameter increased by 1/2" (12.7 mm). Firebox heating surface area included 9 sq ft (0.84 sq m) of arch tubes.

Principal Dimensions by Steve Llanso of Sweat House Media
ClassTT-1 - superheated
Locobase ID817 818
RailroadNorthern Pacific (NP)Northern Pacific (NP)
CountryUSAUSA
Whyte2-6-22-6-2
Number in Class15011
Road Numbers2300-24492450, 2452, 2454-2457, 2459-2462, 2465
GaugeStdStd
Number Built150
BuilderAlco-BrooksNP
Year19061926
Valve GearWalschaertStephenson
Locomotive Length and Weight
Driver Wheelbase (ft / m)11 / 3.3511 / 3.35
Engine Wheelbase (ft / m)28.92 / 8.8128.92 / 8.81
Ratio of driving wheelbase to overall engine wheebase 0.38 0.38
Overall Wheelbase (engine & tender) (ft / m)57.29 / 17.46
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)153,500 / 68,946156,000 / 70,760
Engine Weight (lbs / kg)204,500 / 95,028208,500 / 94,574
Tender Loaded Weight (lbs / kg)139,500 / 67,359148,500 / 67,359
Total Engine and Tender Weight (lbs / kg)344,000 / 162,387357,000 / 161,933
Tender Water Capacity (gals / ML)7000 / 30.308000 / 30.30
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)12 / 10.9012 / 10.90
Minimum weight of rail (calculated) (lb/yd / kg/m)85 / 42.5087 / 43.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)63 / 160063 / 1600
Boiler Pressure (psi / kPa)200 / 13.80200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)21" x 28" / 533x71121.5" x 28" / 546x711
Tractive Effort (lbs / kg)33,320 / 15113.7234,926 / 15842.19
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.61 4.47
Heating Ability
Firebox Area (sq ft / m2)235 / 21.84235 / 21.83
Grate Area (sq ft / m2)43.50 / 4.0443.50 / 4.04
Evaporative Heating Surface (sq ft / m2)2340 / 217.471898 / 176.33
Superheating Surface (sq ft / m2)400 / 37.16
Combined Heating Surface (sq ft / m2)2340 / 217.472298 / 213.49
Evaporative Heating Surface/Cylinder Volume208.47161.32
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation87008700
Same as above plus superheater percentage870010,179
Same as above but substitute firebox area for grate area47,00054,990
Power L1657611,910
Power MT283.34504.94

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