Southern Pacific 4-10-2 Locomotives in the USA

Class Details by Steve Llanso of Sweat House Media

Class SP-1/SP-2/SP-3 (Locobase 288)

Data from 1930 Locomotive Cyclopedia tables and SP Menke All-Time Steam Loco Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. The latter shows the following changes in heating surface areas in all three classes: Firebox heating surface measured at 401 sq ft (up 11 sq ft) and a commensurate increase in total evaporative heating surface. Superheating surface dropped by 116 sq ft to 1,384 sq ft.

Valve motion had limited cutoff. The central piston had a stroke of 28 inches. As with all SP engines, this one was oil-fired. The wheel arrangement was given the name "Southern Pacific" on the Espee, "Overland" on the Union Pacific.

HB Comstock contends that the SP 4-10-2s ran quite well. His assessment may well derive from Alfred W Bruce's encomium found in The Steam Locomotive in America - Its development in the twentieth century (New York: W W Norton, 1952), p 301) . There Bruce contends that "...the use of three cylinders permitted the power to be delivered directly to two driving axles with good balancing conditions in the 63-in driving wheels. The outside piston and main rods were unusually long but produced no ill effects." The inside valve was operated by Gresley conjugated gear, the outside valves by Walschaert radial gear.

The result of this particular union of boiler and running gear: "Combustion conditions were excellent, and the engines performed well at operating speeds of from 30 to 35 miles per hour with the 63-in drivers." Bruce adds, however, "Long continuous operation at higher speeds ...increased the maintenance, as might be expected with the heavy middle-engine moving parts."

Drury (1993) notes that they were too rigid for the curves snaking through the Donner Pass, where they were first tried. After relocation to the Sunset Route east of Los Angeles, the 4-10-2s ran until the mid-1950s. It is there - between Roseville and Summit, Calif on a 2 1/2%, 80-mile grade -- Bruce says, "...the engines were remarkably successful because the operating condtions prevented excessive speeds and the even torque of the three cylinders prevented undue stalling at low speeds."

The original tender behind the 5000 held 12,000 US ga(45,420 litres) of water and 4,000 US gal (15,140 litres) of fuel oil. It weighed 113,000 lb (58,967 kg) empty and 244,900 lb(111,085 kg) loaded. Later FTTs were delivered with tenders that carried 150 more gallons of water and 912 additional gallons of fuel oil. They weighed 264,500 lb (119,975 kg).

Principal Dimensions by Steve Llanso of Sweat House Media
Locobase ID288
RailroadSouthern Pacific (SP)
Number in Class49
Road Numbers5000-5048
Number Built49
Valve Gearmixed
Locomotive Length and Weight
Driver Wheelbase (ft / m)22.83 / 6.96
Engine Wheelbase (ft / m)45.25 / 13.79
Ratio of driving wheelbase to overall engine wheebase 0.50
Overall Wheelbase (engine & tender) (ft / m)88.37 / 26.94
Axle Loading (Maximum Weight per Axle) (lbs / kg)
Weight on Drivers (lbs / kg)316,000 / 143,335
Engine Weight (lbs / kg)445,000 / 201,849
Tender Loaded Weight (lbs / kg)292,700 / 132,767
Total Engine and Tender Weight (lbs / kg)737,700 / 334,616
Tender Water Capacity (gals / ML)16,152 / 61.18
Tender Fuel Capacity (oil/coal) (gals/tons / ML/MT)4912 / 18.60
Minimum weight of rail (calculated) (lb/yd / kg/m)105 / 52.50
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)63.50 / 1613
Boiler Pressure (psi / kPa)225 / 15.50
High Pressure Cylinders (dia x stroke) (in / mm)25" x 32" / 635x813
Low Pressure Cylinders (dia x stroke) (in / mm)25" x 28" / 635x711 (1)
Tractive Effort (lbs / kg)86,589 / 39276.16
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.65
Heating Ability
Firebox Area (sq ft / m2)390 / 36.23
Grate Area (sq ft / m2)89.60 / 8.32
Evaporative Heating Surface (sq ft / m2)5676 / 527.31
Superheating Surface (sq ft / m2)1500 / 139.35
Combined Heating Surface (sq ft / m2)7176 / 666.66
Evaporative Heating Surface/Cylinder Volume312.20
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation20,160
Same as above plus superheater percentage24,394
Same as above but substitute firebox area for grate area106,178
Power L119,249
Power MT671.47