Northern Pacific 2-8-8-4 Yellowstone Type Locomotives

Class Z-5 (Locobase 335)

Note the large firebox with thermic syphons, suitable for burning low-calorie "Rosebud coal." Valve motion limited cutoff. 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 first engine (5000) was built by Alco-Schenectady. Tonnage rating over a ruling grade of 1.1% was 4,000 tons. Later rebuilt with roller bearings and run at a higher boiler pressure, producing 145,930 lb of tractive effort.

Known as "Yellowstones" and gave the name to the wheel arrangement.

Data confirmed by locomotive diagrams from 1949 hosted on http://www.nprr.org/Steam%20Diagrams/Forms/AllItems.aspx (7 Feb 2004).

Specifications
ClassZ-5
Locobase ID335
RailroadNorthern Pacific (NP)
Whyte2-8-8-4
Road Numbers5001-5011
GaugeStd
BuilderBaldwin
Year1928
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase16.75'
Engine Wheelbase66.66'
Ratio of driving wheelbase to overall engine wheebase 0.25
Overall Wheelbase (engine & tender)
Axle Loading (Maximum Weight per Axle)79900 lbs
Weight on Drivers553000 lbs
Engine Weight717000 lbs
Tender Light Weight401000 lbs
Total Engine and Tender Weight1118000 lbs
Tender Water Capacity21000 gals
Tender Fuel Capacity (oil/coal)27 tons
Minimum weight per yard of rail on which locomotive could run115.21 lb rail
Geometry Relating to Tractive Effort
Driver Diameter63"
Boiler Pressure250 psi
Cylinders (dia x stroke)26" x 32" (4)
Tractive Effort145930 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.79
Heating Ability
Firebox Area872 sq. ft
Grate Area182 sq. ft
Evaporative Heating Surface7673
Superheating Surface3219
Combined Heating Surface10892
Evaporative Heating Surface/Cylinder Volume195.10
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation45500
Same as above plus superheater percentage58946.98
Same as above but substitute firebox area for grate area282427.29
Power L127368.61
Power MT872.87

Photos

Reference

Credits

Introduction and specifications provided by Steve Llanso of Sweat House Media.

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