St. Paul & Tacoma Logging Co 2-6-6-2 "Mallet Mogul" Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class unknown (Locobase 4063)

Data from . See also DeGolyer, Vol 71, pp. 358+. Works numbers were 56322 in March 1923 and 57600 in January 1924.

This was an unusual variant on the basic Baldwin articulated-tank in several ways. Whereas the typical example had superheaters and piston valves on all cylinders and were equipped with either saddle tanks or long rectangular tanks, this pair had saturated boilers and slide valves feeding both HP and LP cylinders. Boxy tanks relatively high on the boiler and separated into two units per side. The 7's tanks were connected side-to-side by 5" (127 mm) pipes at the bottom and 6" (152 mm) pipes between the ends on each side at the bottom. 10 had larger pipes.

Two "Hereafter" notes entered in the specs on 16 February 1926 suggested raising questions, one "as to raising cab roof and windows" and the other "about changing articulation joint to a hinged construction. Company reported broken frames on 16 28 46 1/4 DD 13."

The pair operated out of Ohop, Wash until 1950, when they were both retired and scrapped.

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID4063
RailroadSt. Paul & Tacoma Logging Co
Number in Class2
Road Numbers7, 10
Number Built2
Valve GearWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)8
Engine Wheelbase (ft / m)37.75
Ratio of driving wheelbase to overall engine wheebase 0.21
Overall Wheelbase (engine & tender) (ft / m)37.75
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)176,000
Engine Weight (lbs / kg)208,000 / 94,347
Tender Loaded Weight (lbs / kg)
Total Engine and Tender Weight (lbs / kg)208,000
Tender Water Capacity (gals / ML)2500 / 7.58
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)1000 / 3.80
Minimum weight of rail (calculated) (lb/yd / kg/m)49 / 24.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)44 / 1118
Boiler Pressure (psi / kPa)200 / 13.80
High Pressure Cylinders (dia x stroke) (in / mm)17" x 24" / 432x610
Low Pressure Cylinders (dia x stroke) (in / mm)26" x 24" / 660x610
Tractive Effort (lbs / kg)37,545 / 17030.15
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.69
Heating Ability
Firebox Area (sq ft / m2)126
Grate Area (sq ft / m2)26.20 / 2.42
Evaporative Heating Surface (sq ft / m2)2083
Superheating Surface (sq ft / m2)
Combined Heating Surface (sq ft / m2)2083
Evaporative Heating Surface/Cylinder Volume330.37
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation5240
Same as above plus superheater percentage5240
Same as above but substitute firebox area for grate area25,200
Power L12698
Power MT202.77

All material Copyright ©
Wes Barris