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 the encomium found in Alfred Bruce (The Steam Locomotive in America, 1950, pp 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."
| Specifications | |
|---|---|
| Class | SP-1/SP-2/SP-3 |
| Locobase ID | 288 |
| Railroad | Southern Pacific (SP) |
| Whyte | 4-10-2 |
| Road Numbers | 5000-5048 |
| Gauge | Std |
| Builder | Alco-Schenectady |
| Year | 1925 |
| Valve Gear | mixed |
| Locomotive Length and Weight | |
| Driver Wheelbase | 22.83' |
| Engine Wheelbase | 45.25' |
| Ratio of driving wheelbase to overall engine wheebase | 0.50 |
| Overall Wheelbase (engine & tender) | 88.37' |
| Axle Loading (Maximum Weight per Axle) | |
| Weight on Drivers | 316000 lbs |
| Engine Weight | 445000 lbs |
| Tender Light Weight | |
| Total Engine and Tender Weight | 0 |
| Tender Water Capacity | 16000 gals |
| Tender Fuel Capacity (oil/coal) | 4912 gals |
| Minimum weight per yard of rail on which locomotive could run | 105 lb rail |
| Geometry Relating to Tractive Effort | |
| Driver Diameter | 63.50" |
| Boiler Pressure | 225 psi |
| Cylinders (dia x stroke) | 25" x 32" (3) |
| Tractive Effort | 90354 lbs |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | 3.50 |
| Heating Ability | |
| Firebox Area | 390 sq. ft |
| Grate Area | 89.60 sq. ft |
| Evaporative Heating Surface | 5676 |
| Superheating Surface | 1500 |
| Combined Heating Surface | 7176 |
| Evaporative Heating Surface/Cylinder Volume | 208.13 |
| Computations Relating to Power Output (More Information) | |
| Robert LeMassena's Power Computation | 20160 |
| Same as above plus superheater percentage | 24192 |
| Same as above but substitute firebox area for grate area | 105300 |
| Power L1 | 18447 |
| Power MT | 643.49 |
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