Northern Pacific 2-6-6-2 Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class Z (Locobase 1046)

Data confirmed by locomotive diagrams from 1900 hosted on (7 Feb 2004) and Tom Farin's . See also Baldwin Locomotive Works Specification for Engines as digitized by the DeGolyer Library of Southern Methodist University, Volume 30, pp. 14-15. Works numbers were 30566 in April 1907; 31185-31187, 31245, 31307-31308, 31389-31394 in July; 31484, 31514, 31557 in August.

Identical to the Great Northern's L-1s (Locobase 819) and fitted with a Belpaire firebox. Placed in helper service where they were rated at 850 tons up 2.2% grades. These were slow-speed engines, held by the railroad to 15 mph or less.

A 10 December 1907 report in the Baldwin specs file summarized interviews held with General Manager George P Slade, Superintendent of Motive Power William Moir, and Mechanical Manager W L Kinsell. "The above gentlemen, although interviewed separately , united in commenting favorably on the work done by the Mallet compound locomotives now operating west of Livingston."

The letter goes on to report on the "howevers" that such an opening often preceded. Most were relatively minor, as in the ash pans being too level and too close to the grate, which led to grate-bar burnthroughs. A criticism of the starting-valve pipes' small diameter, which the railroad had remedied by installing 1 1/4" pipes, was annotated "These were specified to be 1" dia."

But "the most serious trouble complained of is due to the loosening and leaking of the studs holding the bearing saddle to the waist of the boiler." Not only was repair time-consuming and immobilizing, but the steam and water leakage onto the bearing surfaces might lead to derailments, they feared.

Class Z-1 (Locobase 821)

Data confirmed by locomotive diagrams from 1900 hosted on (7 Feb 2004). Works numbers were 34389-34390 in March 1910; 34422, 34451-34452, 34483 in April.

Follow-ons to the Zs (record 1046), but significantly lighter and fitted with smaller cylinders. As with the Zs, these were a copy of a Great Northern design, in this case the L2 (Locobase 3554).

Specifications by Steve Llanso of Sweat House Media
Locobase ID1046 821
RailroadNorthern Pacific (NP)Northern Pacific (NP)
Number in Class166
Road Numbers3000-30153100-3105
Number Built166
BuilderBurnham, Williams & CoBaldwin
Valve GearWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase10' 9.83'
Engine Wheelbase44.83'43.75'
Ratio of driving wheelbase to overall engine wheebase 0.22 0.22
Overall Wheelbase (engine & tender)73.17'
Axle Loading (Maximum Weight per Axle)57000 lbs
Weight on Drivers316000 lbs250000 lbs
Engine Weight355000 lbs305150 lbs
Tender Light Weight152700 lbs154700 lbs
Total Engine and Tender Weight507700 lbs459850 lbs
Tender Water Capacity8000 gals8000 gals
Tender Fuel Capacity (oil/coal)3449 gals13 tons
Minimum weight of rail (calculated)88 lb/yard69 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter55"55"
Boiler Pressure200 psi210 psi
High Pressure Cylinders (dia x stroke)21.5" x 32"20" x 30"
Low Pressure Cylinders (dia x stroke)33" x 32" (2)31" x 30" (2)
Tractive Effort64193 lbs54999 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.92 4.55
Heating Ability
Firebox Area225 sq. ft214 sq. ft
Grate Area78 sq. ft53.42 sq. ft
Evaporative Heating Surface5608 sq. ft4007 sq. ft
Superheating Surface
Combined Heating Surface5608 sq. ft4007 sq. ft
Evaporative Heating Surface/Cylinder Volume417.07367.33
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation1560011218
Same as above plus superheater percentage1560011218
Same as above but substitute firebox area for grate area4500044940
Power L138973729
Power MT163.13197.30


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