Portland & Southwestern 2-6-6-2 "Mallet Mogul" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class 2 (Locobase 4059)

Data from Jon Davis's loggingmallets.railfan.net/list/prtlnd2/portland2.htm, a logging locomotive website last accessed 19 May 2006 as well as Baldwin Locomotive's Record of Recent Construction 57 -- Oil-Burning Locomotives (1911), 29. Works number was 34785 in December 1910.

Running under Chapman Timber oversight, this engine operated out of Scapoose for only eight years. She then went to the Alton & Southern (in East St Louis, Ill.).

Davis's account pays special attention to the Baldwin "separable boiler" in a description that outdoes others in clarity. The rear part of the boiler had the firetubes common to all "Stephenson" boilers, although these were uncommonly short. The front half of the barrel had two bundles of tubes. In the back part of the front half (still with me?) rested a flue-gas feed water heater offering a total of 1,006 sq ft of surface to heat incoming tender water. A reheater in the smokebox (the 421 sq ft attributed to the "superheater" in the specs) was an intermediate point in the cycle where the exhausting steam from the HP cylinders was reheated before entering the LP cylinders.

Baldwin promoted this concept extensively for a few years, but almost all such Mallets were rebuilt with a standard boiler within a few years. Remarkably, this lone logger seems to have kept its oddly laid out boiler until it was scrapped.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID4059
RailroadPortland & Southwestern
Number in Class1
Road Numbers2
Number Built1
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)9 / 2.74
Engine Wheelbase (ft / m)26.75 / 8.15
Ratio of driving wheelbase to overall engine wheebase 0.34
Overall Wheelbase (engine & tender) (ft / m)42 / 12.80
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)204,500 / 92,760
Engine Weight (lbs / kg)235,300 / 106,730
Tender Loaded Weight (lbs / kg)99,700 / 45,223
Total Engine and Tender Weight (lbs / kg)335,000 / 151,953
Tender Water Capacity (gals / ML)5000 / 18.94
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)2000 / 7.60
Minimum weight of rail (calculated) (lb/yd / kg/m)57 / 28.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)51 / 1295
Boiler Pressure (psi / kPa)200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)18.5" x 28" / 470x711
Low Pressure Cylinders (dia x stroke) (in / mm)28" x 28" / 711x711
Tractive Effort (lbs / kg)44,472 / 20172.18
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.60
Heating Ability
Firebox Area (sq ft / m2)148 / 13.75
Grate Area (sq ft / m2)41.80 / 3.88
Evaporative Heating Surface (sq ft / m2)2904 / 269.89
Superheating Surface (sq ft / m2)421 / 39.13
Combined Heating Surface (sq ft / m2)3325 / 309.02
Evaporative Heating Surface/Cylinder Volume333.36
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation8360
Same as above plus superheater percentage9447
Same as above but substitute firebox area for grate area33,448
Power L16332
Power MT409.57

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