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 from DeGolyer, Volume 30, pp. 350+. See also 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). They had straight boilers, 13" (330 mm) piston valves serving the HP cylinders and slide valves on the LPs, and small fireboxes with wide grates.

3103 was retired in August 1932, 3101 in June 1934, and 3104-3105 in October 1934. 3102 lasted until October 1940

3100 was sold to Polson Logging Company in December 1940. Operating out of Railroad Camp, Wash, the 3100 operated until 1945 with the Polson herald on its tender, then for successor company Rayonier, Inc until 1959.

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 Wheelbase (ft)10 9.83
Engine Wheelbase (ft)44.8343.75
Ratio of driving wheelbase to overall engine wheebase 0.22 0.22
Overall Wheelbase (engine & tender) (ft)73.17
Axle Loading (Maximum Weight per Axle) (lbs)57,00049,600
Weight on Drivers (lbs)316,000262,350
Engine Weight (lbs)355,000305,150
Tender Loaded Weight (lbs)152,700154,700
Total Engine and Tender Weight (lbs)507,700459,850
Tender Water Capacity (gals)80008000
Tender Fuel Capacity (oil/coal) (gals/tons)344913
Minimum weight of rail (calculated) (lb/yd)8873
Geometry Relating to Tractive Effort
Driver Diameter (in)5555
Boiler Pressure (psi)200210
High Pressure Cylinders (dia x stroke) (in)21.5" x 32"20" x 30"
Low Pressure Cylinders (dia x stroke) (in)33" x 32"31" x 30"
Tractive Effort (lbs)64,19354,999
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.92 4.77
Heating Ability
Firebox Area (sq ft)225186
Grate Area (sq ft)7853.42
Evaporative Heating Surface (sq ft)56084007
Superheating Surface (sq ft)
Combined Heating Surface (sq ft)56084007
Evaporative Heating Surface/Cylinder Volume417.07367.33
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation15,60011,218
Same as above plus superheater percentage15,60011,218
Same as above but substitute firebox area for grate area45,00039,060
Power L138973626
Power MT163.13182.82


If you have any railroad data such as diagram books, rail station plans or anything else that you would be willing to share, please contact us.