These were known as "Yellowstones" and gave the name to the wheel arrangement. The first engine (5000) was built by Alco-Schenectady and had works number 67578. Its adhesion weight came to 553,000 lb (2251,230 kg) and total engine weight amounted to 717,000 lb (325,226 kg). Maximum axle loading was 70,500 lb (31,978 kg). For some reason, this mostly Alco road then gave the production order to Baldwin.
Note the large firebox suitable for burning low-calorie "Rosebud coal." Valve motion limited cutoff of the 14" piston valves, which had a maximum travel of 7 1/2" (191 mm). When the original firebox proved too large to sustain a high-enough temperature and permit complete combustion of the fuel, the fix was installing a Gaines' wall two feet from the front of the firebox, effectively reducing the size of the grate, but increasing the interior temperature. The brick arch was to be located such that the area above the arch was at least 100% of the flue area.
Three Nicholson thermic syphons in the firebox and two in the combustion chamber contributed 256 sq ft (23.8 sq m) to direct heating surface area. The combustion chamber itself added another 162 sq ft (15.05 sq m). The design also featured Type B Dupont Simplex stokers with a capacity of 20 short tons of coal per hour, Alco Type G power reverse gear, and a Coffin feedwater heater.
Tonnage rating over a ruling grade of 1.1% was 4,000 tons (3,636 metric tons). This class was rebuilt with Timken roller bearings in 1944, given a sturdier front frame, had steam leaks sealed, and run at a higher boiler pressure, producing 145,930 lb (66,193 kg) of tractive effort.
|Specifications by Steve Llanso of Sweat House Media|
|Railroad||Northern Pacific (NP)|
|Locomotive Length and Weight|
|Ratio of driving wheelbase to overall engine wheebase||0.25|
|Overall Wheelbase (engine & tender)||110.08'|
|Axle Loading (Maximum Weight per Axle)||70900 lbs|
|Weight on Drivers||558900 lbs|
|Engine Weight||723400 lbs|
|Tender Light Weight||402000 lbs|
|Total Engine and Tender Weight||1125400 lbs|
|Tender Water Capacity||21200 gals|
|Tender Fuel Capacity (oil/coal)||27 tons|
|Minimum weight of rail (calculated)||116 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||250 psi|
|Cylinders (dia x stroke)||26" x 32"|
|Tractive Effort||145930 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||3.83|
|Firebox Area||872 sq. ft|
|Grate Area||182 sq. ft|
|Evaporative Heating Surface||7673 sq. ft|
|Superheating Surface||3219 sq. ft|
|Combined Heating Surface||10892 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||195.10|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||45500|
|Same as above plus superheater percentage||59150|
|Same as above but substitute firebox area for grate area||283400|