Northern Pacific 2-8-8-4 "Yellowstone" Locomotives in the USA

Northern Pacific Yellowstone

The first Yellowstone was built in 1928 by ALCO for the Northern Pacific for running throughout the high speed plains of North Dakota. It would turn out to be the one and only Yellowstone that ALCO would build.

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.

Class Details by Steve Llanso of Sweat House Media

Class Z-5 (Locobase 335)

Data from tables in 1930 Locomotive Cyclopedia, confirmed by locomotive diagrams from 1949 hosted on [] (7 Feb 2004). See also DeGolyer, Volume 82, pp. 307+; and "Largest Locomotive Ever Built - Northern Pacific Railway", Railway Journal, Volume 35, No 2 (February 1929), pp. 22; and NP Locomotive Data Cards supplied in August 2013 by Allen Stanley from his extensive Rail Data Exchange collection. (Thanks to Bill Hoehn, whose 11 February 2013 inquiry about the 1941 update led to Locobase's revision of this entry and to Chris Hohl, whose 7 March 2015 email provided a correction on the tender's coal capacity; and Ray Uhlich, whose 10 November 2020 email supplied the reason for awarding the production contract to Baldwin.) Baldwin works numbers were 61292-61293 in April 1930; 61356-61358, 61380-61381 in May; 61419-61420, 61434 in July; and 61495 in September.

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).

Locobase originally began this paragraph with "Then for some reason, this mostly Alco road then gave the production order to Baldwin." Ray Uhlich gave the simple answer in his email. According to his father, a mechanical inspector for the NP, Baldwin bid a lower amount for the contract. Locobase adds that especially considering the country had begun its descent into the Great Depression, building large articulateds must have extended quite a few jobs.

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 feed in water heater.

A 1941 update installed Timken roller bearings in December 1941 at the cost of $19,059.74 for each engine.

Tonnage rating over a ruling grade of 1.1% was 4,000 tons (3,636 metric tons). This class was 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 NP removed the feed water heater and boosters in 1948-1949.

Principal Dimensions by Steve Llanso of Sweat House Media

Locobase ID335
RailroadNorthern Pacific (NP)
Number in Class11
Road Numbers5001-5011
Number Built11
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)33.50 / 10.21
Engine Wheelbase (ft / m)66.66 / 20.32
Ratio of driving wheelbase to overall engine wheelbase 0.50
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 / Liters/MT)27 / 25
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
Booster (lbs)13,400
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.83
Heating Ability
Tubes (number - dia) (in / mm)92 - 2.25" / 57
Flues (number - dia) (in / mm)280 - 3.5" / 89
Flue/Tube length (ft / m)22 / 6.71
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 Volume195.09
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation45,500
Same as above plus superheater percentage59,150
Same as above but substitute firebox area for grate area283,400
Power L127,367
Power MT863.61

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Wes Barris