loco-info.com - Soo Line class N-20

No. 4000 in May 1954 at North Fond du Lac, Wisconsin

Harold K. Vollrath

These updated USRA Light Mountains were built to accelerate freight traffic on a single track main line. The first ten were built by ALCO-Brooks in 1926, eight more in 1928 by ALCO in Schenectady, and the last three in 1930 by the Soo Line's Shoreham Works in Minneapolis. There were minimal differences in weight between the individual series. The tenders initially had a capacity of 10,000 gallons of water and 16 short tons of coal. These were later enlarged and some locomotives also received completely new, larger tenders.

General
Built	1926-1930
Manufacturer	ALCO, Shoreham
Axle config	4-8-2 (Mountain)
Gauge	4 ft 8 1/2 in (Standard gauge)

Dimensions and Weights
Length	88 ft 4 1/2 in
Wheelbase	40 ft 10 in
Rigid wheelbase	18 ft 3 in
Service weight	342,000 lbs
Adhesive weight	231,500 lbs
Total weight	513,800 lbs
Axle load	57,900 lbs
Water capacity	12,000 us gal
Fuel capacity	35,000 lbs (coal)

Boiler
Grate area	70.3 sq ft
Firebox area	341 sq ft
Tube heating area	3,448 sq ft
Evaporative heating area	3,789 sq ft
Superheater area	1,103 sq ft
Total heating area	4,892 sq ft

Power Plant
Driver diameter	69 in
Boiler pressure	200 psi
Expansion type	simple
Cylinders	two, 27 x 30 in

Power
Power source	steam
Estimated power	3,250 hp (2,424 kW)
Starting effort	53,883 lbf
Booster	11,800 lbf

Calculated Values
Factor of adhesion	1 : 4.30
Optimal speed	38 mph
Power-to-weight ratio	0.0095 hp/lb
Heating Area Equivalent	7,700 sq ft
Cylinder volume/HAE	1 : 786.95
Adhesive weight/Total	1 : 1.48
Tractive force/Heating area	1 : 2478.57
Grate area/Heating area	1 : 64.74
Firebox/Tube area	1 : 13.35
Total/Superheater	1 : 3.44

steam locomotive

freight

booster

last changed: 03/2023

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