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Chicago, Milwaukee, St. Paul & Pacific (Milwaukee Road) classes S1 to S3
United States | 1930 | 52 produced
S-2 No. 202 in November 1937 in Bensenville, Illinois
S-2 No. 202 in November 1937 in Bensenville, Illinois
collection Taylor Rush

The history of the 4-8-4 at Milwaukee Road began in 1930 with the single number 9700, which later became the 250, and was supplied by Baldwin. Its power was guaranteed by a boiler with a combustion chamber, thermic syphons, arch tubes and a coffin feed water heater. Since the 4-6-4 class F6 was sufficient for the express trains of the time, it initially remained a one-off and was used in front of freight trains weighing up to 5,000 tons. It was only when the express trains became increasingly heavier that the 250 was used for this purpose.

It was not until 1938 that the Milwaukee Road manufactured the 251 in their own shops, which was a copy of the 250 and together with it formed the class S1. As early as 1937, Baldwin had started producing the 40 class S2 locomotives, which had some changes compared to the S1 and was more powerful, not least due to the boiler pressure of 285 psi. During the Second World War, ALCO built ten S3 which had a smaller boiler with only 250 psi and did not have much in common with the S1 and S2 in terms of design. Today only the two S3 numbered 261 and 265 still exist, the former of which is operational.

VariantS1S2S3
General
Built1930, 19381937-1938, 19401943
ManufacturerBaldwin, MilwaukeeBaldwinALCO
Axle config4-8-4 (Northern) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Wheelbase46 ft 3 in47 ft 4 in46 ft 7 in
Fixed wheelbase19 ft 9 in19 ft 3 in19 ft 9 in
Total wheelbase88 ft 4 in92 ft 0 1/2 in95 ft 6 1/2 in
Service weight450,840 lbs490,450 lbs460,000 lbs
Adhesive weight258,818 lbs282,320 lbs259,300 lbs
Total weight740,009 lbs813,450 lbs824,100 lbs
Axle load65,136 lbs
Water capacity15,000 us gal20,000 us gal
Fuel capacity40,000 lbs (coal)50,000 lbs (coal)
Power
Power sourcesteam
Estimated power4,650 hp (3,468 kW)5,300 hp (3,952 kW)4,700 hp (3,505 kW)
Optimal speed48 mph
Starting effort62,137 lbf70,816 lbf62,119 lbf
Power Plant
Driver diameter74 in
Boiler pressure230 psi285 psi250 psi
Expansion typesimple
Cylinderstwo, 28 x 30 intwo, 26 x 32 in
Boiler
Grate area103 sq ft106 sq ft96.2 sq ft
Firebox area549 sq ft578 sq ft505.5 sq ft
Tube heating area4,851 sq ft4,931 sq ft3,972.5 sq ft
Evaporative heating area5,400 sq ft5,509 sq ft4,478 sq ft
Superheater area2,403 sq ft2,336 sq ft1,438 sq ft
Total heating area7,803 sq ft7,845 sq ft5,916 sq ft
Calculated Values
steam locomotive
freight
express
last changed: 02/2024
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