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Nashville, Chattanooga & St. Louis class H7

United States 1903 36 produced
H7A-37 No. 408 in August 1940 at Memphis, Tennessee Arthur B. Johnson collection

The H7 was a class of 36 Consolidations built by Baldwin for the NC&StL between 1903 and 1907. Compared to the H6 introduced in 1902, they had a larger tube surface, but were identical in other dimensions. This included drivers of 56 inches, 21 by 28 inch cylinders, a grate of 46,6 square feet and a boiler pressure of 195 psi. The first batch of ten was designated H7-37 due to their starting tractive effort of roughly 37,000 pounds, identical to the H6-37.

Next were 16 H7A-37 and ten H7B-37 which had fewer tubes. While the original H7 and the H7A had Stephenson valve gear, the H7B was built with Walschaerts valve gear. Starting in 1918, the railroad's own workshops started to superheat the class. They now had a boiler pressure of only 180 psi, but the cylinder diameter had been increased to 23 inches. As this resulted in a higher starting tractive effort, they were designated H7C-40. The class was retired between 1946 and 1951.

Technical data

General

Property H7-37 H7B-37 rebuilt H7C-40
Built 1903 1907 ab 1918
Manufacturers Baldwin Nashville
Wheel arrangement 2-8-0 (Consolidation)
Gauge 1,435 mm (Standard gauge)

Dimensions and weights

Property H7-37 H7B-37 rebuilt H7C-40
Length 19.40 m 18.72 m
Wheelbase 7.21 m
Total wheelbase 16.02 m
Empty mass 68.2 t 70.9 t
Service mass 75.4 t 77.2 t
Adhesion mass 68.2 t 69.5 t
Total mass 124.9 t 126.7 t
Rigid wheelbase 4.67 m
Water capacity 18,927 l 20,820 l
Fuel capacity 9.5 t (coal)

Boiler

Property H7-37 H7B-37 rebuilt H7C-40
Grate area 4.329 m²
Firebox surface 15.925 m² 15.991 m² 17.744 m²
Tube heating surface 211.434 m² 184.1 m² 157.564 m²
Evaporative heating surface 227.359 m² 200.091 m² 175.308 m²
Total heating surface 227.4 m² 200.1 m² 212.9 m²
Superheater surface 37.626 m²

Power plant

Property H7-37 H7B-37 rebuilt H7C-40
Driver diameter 1,422 mm
Boiler pressure 13.4 bar 12.4 bar
Expansion type simple expansion
Cylinders two, 533 x 711 mm two, 584 x 711 mm

Power

Property H7-37 H7B-37 rebuilt H7C-40
Power source steam
Estimated power 895 kW 969 kW
Starting effort 162.6 kN 180.0 kN

Calculated values

Property H7-37 H7B-37 rebuilt H7C-40
Factor of adhesion 1 : 4.11 1 : 3.79
Optimal speed 34 km/h 32 km/h
Power-to-weight ratio 11.9 kW/t 12.5 kW/t
Heating Surface Equivalent 307.0 m² 280.0 m² 339.3 m²
Cylinder volume/HSE 1 : 1,035.39 1 : 1,134.98 1 : 1,123.77
Adhesive weight/Total 1 : 1.11
Tractive force/Heating surface 1 : 14.93 1 : 16.97 1 : 17.66
Grate area/Heating surface 1 : 52.52 1 : 46.22 1 : 49.19
Firebox/Tube surface 1 : 13.28 1 : 11.51 1 : 8.88
Total/Superheater 1 : 4.66
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