An oddball 1910 design that was fitted with 655 sq ft of "reheater" placed in the smoke box and in the path of the steam exiting the HP cylinders. The idea was to re-energize the exhausted steam before conducting it to the LP cylinders. The boiler also had a feedwater heater with 401 2 1/4" tubes measuring 5' 3" long that was credited with 1,270 sq ft. Because none of this additional area actually superheated anything, Locobase includes it all in the evaporative heating surface total.
Rebuilt 1920-1921 and 1925.
Locobase 848 describes the saturated-boiler version that was delivered in 1910. When the design was superheated, the result was a relatively small articulated locomotive. The later Z articulateds would be considerably larger.
The small tender indicates the role of pusher locomotive on the Bozeman Pass, in which role it performed in 1945.
NB: The direct heating surface (including the firebox heating surface) is an estimate calculated by subtracting the calculated tube heating surface from the reported total evaporative heating surface.
Schenectady built the first 10 of these big articulateds in 1913 as the first superheated articulated locomotives on the NP. Brooks added 11 more in 1917 and 1920; see Locobase 849.
Arch tubes contributed 41.6 sq ft of firebox heating surface. It's not clear if the two coal burners (4005 and 4008) shown in the NP diagram book were the last two to use coal or if the split between coal and oil burners had always been 2 and 9. Drury (1993) notes in a caption that the 40"-diameter cylinders, which look like trash barrels mounted horizontally on the front of the engine, "...signify great tractive effort and little speed." And in fact the RAG noted that the maximum horsepower was generated at 10.6 mph. 14" piston valves fed the HP cylinders while slide valves sufficed for the LP cans.
They were widely used throughout the railroad. The RA report described Z-3 service as follows: "Between Helena and Blossburg a Class W-3 locomotive with a Class Z-3 helper is hauling 1,750 tons with no increase in coal over that formerly used by a Class W and a Class Z-1 handling 1,350 tons. This is an increase of 29.6 per cent in train load, with no increase in coal consumption.
"The new Class Z-3 Mallets are used on the Rocky Mountain and Seattle Divisions, four coal burners on the Rocky Mountain Division and six oil burners on the Seattle Division. The grades and trains on the Rocky Mountain Division are described above, these locomotives being used as helpers between Helena and Blossburg.
"The Seattle Division, from Ellensburg, Wash., to Auburn, Wash., is 105 miles long, crossing the Cascade Mountains through Stampede Tunnel west of Ellensburg at an elevation of 2,837 feet above sea level. These locomotives are handling 2,200 tons from Auburn to Ellensburg at a speed of from eight to 14 miles per hour, on a total oil consumption of 2,645 gallons. From Auburn to Lester, a distance of 43 miles, the average grade is one per cent. From Lester to Easton, a distance of 24 miles, there is a ruling grade of 2.2 per cent for ten miles. [A] Class Z Mallet helper ... is used from Lester to Martin. Westbound, the Z-3 locomotive handles a time freight of 1,900 tons from Ellensburg to Auburn on 1,726 gallons of oil, having a Class Z (2-6-6-2) Mallet helper on the 2.2 per cent grade."
See Locobase 13133 for the first 10 of this class delivered by Schenectady in 1913 and a description of their widespread use. The first 5 of the Brooks class arrived in 1917 and weighed slightly less than the 6 that would follow in 1920. The specifications above are taken from the detailed RAG article of 1921.
Arch tubes contributed 41.6 sq ft of firebox heating surface in a boiler that had a slight rearrangement of tube and flue counts. Eight small tubes were deleted in favor of two flues which resulted in an 80 sq ft increase in superheater area. Like the 1913 engines, these articulateds served their HP cylinders with 14" piston valves and their LP trash cans with slide valves.
In 1921, RAG reported that the new Z-3s were assigned to helper service on steep Rocky Mountain and Montana Division grades. On the Seattle division, they hauled the trains themselves, "...handling 2,400 tons between Auburn and Lester, the grade being uniformly 1.0 per cent. Helpers [were] used from Lester to the summit of the Cascade Mountains."
Identical to the USRA's heavy articulated design.
None of the NP diagrams showed the firebox heating surface separately, so Locobase took the value from the USRA entry (Locobase 330).
|Specifications by Steve Llanso of Sweat House Media|
|Class||Z-2||Z-2 - superheated||Z-3 - 1913||Z-3 - 1917||Z-4|
|Railroad||Northern Pacific (NP)||Northern Pacific (NP)||Northern Pacific (NP)||Northern Pacific (NP)||Northern Pacific (NP)|
|Locomotive Length and Weight|
|Ratio of driving wheelbase to overall engine wheebase||0.27||0.27||0.27||0.27||0.27|
|Overall Wheelbase (engine & tender)||76'||83.54'||94.27'|
|Axle Loading (Maximum Weight per Axle)||59100 lbs||59100 lbs||53700 lbs||56900 lbs||62000 lbs|
|Weight on Drivers||403800 lbs||403800 lbs||399500 lbs||419500 lbs||486000 lbs|
|Engine Weight||437950 lbs||437950 lbs||456000 lbs||483000 lbs||541500 lbs|
|Tender Light Weight||151700 lbs||151700 lbs||193200 lbs||205600 lbs||224800 lbs|
|Total Engine and Tender Weight||589650 lbs||589650 lbs||649200 lbs||688600 lbs||766300 lbs|
|Tender Water Capacity||8000 gals||8000 gals||10000 gals||10000 gals||12000 gals|
|Tender Fuel Capacity (oil/coal)||12 tons||12 tons||3500 gals||16 tons||16 tons|
|Minimum weight of rail (calculated)||84 lb/yard||84 lb/yard||83 lb/yard||87 lb/yard||101 lb/yard|
|Geometry Relating to Tractive Effort|
|Boiler Pressure||200 psi||200 psi||200 psi||200 psi||240 psi|
|High Pressure Cylinders (dia x stroke)||26" x 30"||26" x 30"||26" x 30"||26" x 30"||25" x 32"|
|Low Pressure Cylinders (dia x stroke)||40" x 30" (2)||40" x 30" (2)||40" x 30" (2)||40" x 30" (2)||39" x 32" (2)|
|Tractive Effort||85039 lbs||85039 lbs||85039 lbs||85039 lbs||101465 lbs|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||4.75||4.75||4.70||4.93||4.79|
|Firebox Area||252 sq. ft||377 sq. ft||368 sq. ft||373.60 sq. ft||435 sq. ft|
|Grate Area||84 sq. ft||84 sq. ft||84.20 sq. ft||84.30 sq. ft||96 sq. ft|
|Evaporative Heating Surface||7068 sq. ft||4175 sq. ft||5497 sq. ft||5497 sq. ft||6052 sq. ft|
|Superheating Surface||994 sq. ft||1225 sq. ft||1305 sq. ft||1475 sq. ft|
|Combined Heating Surface||7068 sq. ft||5169 sq. ft||6722 sq. ft||6802 sq. ft||7527 sq. ft|
|Evaporative Heating Surface/Cylinder Volume||383.40||226.47||298.18||298.18||332.88|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||16800||16800||16840||16860||23040|
|Same as above plus superheater percentage||16800||19992||19871||20063||27648|
|Same as above but substitute firebox area for grate area||50400||89726||86848||88917||125280|