Northern Pacific classes WA, WB and W-1
United States 1904 200 produced
The Northern Pacific was the first US railroad to purchase a significant number of Mikados. These machines grouped under the class W were 55 locomotives of the subclass WA without a combustion chamber and 105 WB with a combustion chamber. Some of these were built as compound locomotives and later rebuilt to the simple variant. 40 class W-1 locomotives followed in 1910, which differed mainly in that they had Walschaerts valve gear in contrast to the Stephenson valve gear of their predecessors. Most of the locomotives were superheated from 1912, and the boiler pressure was increased to 200 psi with thicker boiler plates.
Technical data
General
| Property | WA | WB | WA/WB superheated | W-1 |
|---|---|---|---|---|
| Built | 1904 | 1906 | 1912 | 1910 |
| Manufacturers | ALCO | Northern Pacific | ALCO | |
| Wheel arrangement | 2-8-2 (Mikado) | |||
| Gauge | 1,435 mm (Standard gauge) | |||
Dimensions and weights
| Property | WA | WB | WA/WB superheated | W-1 |
|---|---|---|---|---|
| Wheelbase | 10.59 m | |||
| Service mass | 117.5 t | 117 t | 119.5 t | 122.3 t |
| Adhesion mass | 92.3 t | 91.4 t | 93.4 t | 94.8 t |
| Total mass | 184.8 t | 197.7 t | 206.5 t | 209.3 t |
| Rigid wheelbase | 5.03 m | |||
| Axle load | 26.3 t | 26.2 t | 26.6 t | 27 t |
| Water capacity | 30,283 l | 37,854 l | ||
| Fuel capacity | 10.9 t (coal) | 17.2 t (coal) | ||
Boiler
| Property | WA | WB | WA/WB superheated | W-1 |
|---|---|---|---|---|
| Grate area | 4.041 m² | |||
| Firebox surface | 19.417 m² | 22.761 m² | 23.226 m² | 25.084 m² |
| Tube heating surface | 352.846 m² | 301.656 m² | 242.57 m² | 238.111 m² |
| Evaporative heating surface | 372.263 m² | 324.418 m² | 265.796 m² | 263.195 m² |
| Total heating surface | 372.3 m² | 324.4 m² | 318.8 m² | 306.4 m² |
| Superheater surface | 52.955 m² | 43.2 m² | ||
Power plant
| Property | WA | WB | WA/WB superheated | W-1 |
|---|---|---|---|---|
| Driver diameter | 1,600 mm | |||
| Boiler pressure | 11.7 bar | 13.8 bar | 11.7 bar | |
| Expansion type | simple expansion | |||
| Cylinders | two, 610 x 762 mm | two, 635 x 762 mm | ||
Power
| Property | WA | WB | WA/WB superheated | W-1 |
|---|---|---|---|---|
| Power source | steam | |||
| Estimated power | 1,119 kW (1,521 PS) | 1,081 kW (1,470 PS) | 1,305 kW (1,774 PS) | 1,193 kW (1,622 PS) |
| Starting effort | 176.3 kN | 207.4 kN | 191.3 kN | |
Calculated values
| Property | WA | WB | WA/WB superheated | W-1 |
|---|---|---|---|---|
| Factor of adhesion | 1 : 5.14 | 1 : 5.09 | 1 : 4.42 | 1 : 4.86 |
| Optimal speed | 39 km/h | 37 km/h | 39 km/h | |
| Power-to-weight ratio | 9.5 kW/t | 9.2 kW/t | 10.9 kW/t | 9.8 kW/t |
| Heating Surface Equivalent | 469.3 m² | 438.2 m² | 487.8 m² | 475.0 m² |
| Cylinder volume/HSE | 1 : 947.70 | 1 : 1,015.01 | 1 : 911.78 | 1 : 1,016.05 |
| Adhesive weight/Total | 1 : 1.27 | 1 : 1.28 | 1 : 1.29 | |
| Tractive force/Heating surface | 1 : 9.89 | 1 : 11.35 | 1 : 13.59 | 1 : 13.04 |
| Grate area/Heating surface | 1 : 92.12 | 1 : 80.28 | 1 : 78.88 | 1 : 75.82 |
| Firebox/Tube surface | 1 : 18.17 | 1 : 13.25 | 1 : 10.44 | 1 : 9.49 |
| Total/Superheater | 1 : 5.02 | 1 : 6.09 | ||
