NP wanted to burn low-grade Rosebud coal (obtained from mines along the line) in their locomotives. This required the Yellowstone to be designed with a huge (the largest ever used on a steam locomotive) firebox (182 sq. ft.). The front half of the firebox was over the two rear pairs of drivers and the trailing truck (which was equipped with a booster).
It was the largest steam locomotive in the world (at that time) and ALCO celebrated by serving dinner to 12 people seated in the firebox! Remember, this was long before the Big Boys were even a thought. NP asked for bids for 11 more like it and in 1930 Baldwin got the job. The NP Yellowstones steamed poorly and produced less that 5,000 HP. NP found that the grates were simply too large to maintain a high temperature and complete combustion. The combustion problem was solved by blocking off The front two feet of the firebox on each locomotive. At some point the Z-5s were upgraded with roller bearings.
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" (356 mm) 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. (For a full description of the Gaines combustion chamber's intended effect on combustion, see Locobase 4228.)
The Q&C "Nogroth" grate seems to have been a rosebud rocker design, intended "to burn sub-bituminous coal.". The 3/8" (9.5 mm) diameter hole provided air and the perforated plates rocked "both ways" with a 4 1/2" (114.5 mm) opening.
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 (18,144 kg) 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. The feed water heaters were removed in the late 1940s.
|Principal Dimensions by Steve Llanso of Sweat House Media|
|Railroad||Northern Pacific (NP)|
|Number in Class||11|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)||16.75 / 5.11|
|Engine Wheelbase (ft / m)||66.66 / 20.32|
|Ratio of driving wheelbase to overall engine wheebase||0.25|
|Overall Wheelbase (engine & tender) (ft / m)||110.08 / 33.55|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)||70,900 / 32,160|
|Weight on Drivers (lbs / kg)||558,900 / 253,513|
|Engine Weight (lbs / kg)||723,400 / 328,129|
|Tender Loaded Weight (lbs / kg)||402,000 / 182,344|
|Total Engine and Tender Weight (lbs / kg)||1,125,400 / 510,473|
|Tender Water Capacity (gals / ML)||21,200 / 80.30|
|Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)||27 / 24.50|
|Minimum weight of rail (calculated) (lb/yd / kg/m)||116 / 58|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||63 / 1600|
|Boiler Pressure (psi / kPa)||250 / 17.20|
|High Pressure Cylinders (dia x stroke) (in / mm)||26" x 32" / 660x813 (4)|
|Tractive Effort (lbs / kg)||145,930 / 66192.81|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||3.83|
|Firebox Area (sq ft / m2)||872 / 81.01|
|Grate Area (sq ft / m2)||182 / 16.91|
|Evaporative Heating Surface (sq ft / m2)||7673 / 712.84|
|Superheating Surface (sq ft / m2)||3219 / 299.05|
|Combined Heating Surface (sq ft / m2)||10,892 / 1011.89|
|Evaporative Heating Surface/Cylinder Volume||195.10|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||45,500|
|Same as above plus superheater percentage||59,150|
|Same as above but substitute firebox area for grate area||283,400|