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The reference for locomotives and railcars

Nippon Tetsudō Bt4/6

Japanese Government Railways class 9700

Japan 1897 20 produced
PD

These 20 2-8-2 locomotives, which were delivered by Baldwin to the Nippon Railway in 1897, gave this wheel arrangement the name “Mikado”. Their manufacturer called them type 12-30 1/4 E, while their designation on the railway was originally Bt4/6. To burn low-grade coal from the Joban coal fields, they needed a large grate. So a trailing axle was added, above which a wide firebox was mounted. With small drivers of only 45 inches and cylinders which measured 18.5 by 24 inches, they were the most powerful locomotives in Japan at this time.

Their main task was to haul freight trains on the Joban line, located on the east coast of Honshū, north of Tokyo. In 1901 and 1902, five locomotives received a new boiler with a Wootten firebox. With this the firebox heating surface increased from 9.3 to 11.9 square meters, while the tube heating surface decreased from 197.8 to 142.4 square meters. From 1909, the JGR numbered them 9700 to 9719. They were used until 1922.

Technical data

General

Built
1897
Manufacturers
Baldwin
Wheel arrangement
2-8-2 (Mikado)
Gauge
1,067 mm (Cape gauge)

Dimensions and weights

Length
17.27 m
Wheelbase
7.47 m
Total wheelbase
14.48 m
Service mass
55.1 t
Adhesion mass
48.8 t
Total mass
82.3 t
Rigid wheelbase
3.61 m
Axle load
12.2 t
Water capacity
11,356 l
Fuel capacity
5.4 t (coal)

Boiler

Grate area
2.79 m²
Firebox surface
9.824 m²
Tube heating surface
196.064 m²
Evaporative heating surface
205.887 m²
Total heating surface
205.9 m²

Power plant

Driver diameter
1,143 mm
Boiler pressure
12.4 bar
Expansion type
simple expansion
Cylinders
two, 470 x 610 mm

Power

Power source
steam
Estimated power
708 kW (963 PS)
Starting effort
124.2 kN

Calculated values

Factor of adhesion
1 : 3.85
Optimal speed
35 km/h
Power-to-weight ratio
12.8 kW/t
Heating Surface Equivalent
255.0 m²
Cylinder volume/HSE
1 : 829.13
Adhesive weight/Total
1 : 1.13
Tractive force/Heating surface
1 : 12.60
Grate area/Heating surface
1 : 73.79
Firebox/Tube surface
1 : 19.96
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