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Southern Pacific classes SP-1 to SP-3
United States | 1925 | 49 produced
SP-2 No.5018
SP-2 No.5018
R.W. Biermann / collection Taylor Rush

To pull heavy freight and passenger trains over the Sierra Nevada, the Southern Pacific ordered large locomotives for mixed service from ALCO Schenectady in 1925. They were the first locomotives in the USA with the 4-10-2 wheel arrangement, so the SP called them "Southern Pacific", which led to the class designation SP-1.

In order to better cope with the boiler's high output, they had three cylinders. While the outer two each had their own Walschaert valve gear, the middle one was controlled via Gresley's conjugated valve gear. It also had a stroke that was four inches shorter. For starting off, a booster was also installed on the trailing axle

By 1927, 49 locomotives had been built in three batches, designated SP-1 to SP-3. They were initially supposed to be used at Donner Pass, but the five driving axles proved to be too rigid there. They now came to the Sunset Route, which ran east from Sos Angeles, where they pulled heavy trains over the grades at speeds of 30 to 35 mph. Today only SP-2 No. 5021 exists, which was last restored in 1965 and is now in Pomona, California.

General
Built1925-1927
ManufacturerALCO
Axle config4-10-2 (Reid Tenwheeler)
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase45 ft 3 in
Fixed wheelbase22 ft 10 in
Total wheelbase88 ft 3 in
Service weight445,000 lbs
Adhesive weight316,000 lbs
Total weight737,700 lbs
Axle load63,200 lbs
Water capacity12,150 us gal
Fuel capacity4,912 lbs (oil)
Power
Power sourcesteam
Estimated power4,000 hp (2,983 kW)
Optimal speed28 mph
Top speed70 mph
Starting effort91,071 lbf
Booster12,350 lbf
Power Plant
Driver diameter63 in
Boiler pressure225 psi
Expansion typesimple
Cylindersthree, center: 25 x 32 in
outside: 25 x 28 in
Boiler
Grate area89.6 sq ft
Firebox area390 sq ft
Tube heating area5,286 sq ft
Evaporative heating area5,676 sq ft
Superheater area1,500 sq ft
Total heating area7,176 sq ft
Calculated Values
steam locomotive
freight
passenger
booster
last changed: 04/2024
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