The reference for locomotives and railcars


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Pennsylvania class AAn
later classes D7 and D7a
United States | 1882 | 119 produced
D7a No. 953 in an Altoona Works factory photograph
D7a No. 953 in an Altoona Works factory photograph
Pennsylvania Railroad

In order to be able to burn anthracite coal efficiently, class AAn was developed from class K (later D6). The K already had a wide firebox above the drivers, which was optimized here for the use of anthracite. There were 58 locomotives with a coupling wheel diameter of 68 inches, which became class D7 from 1895, and 61 with a coupling wheel diameter of 62 inches, which became class D7a.

Axle config4-4-0 (American) 
Gauge4 ft 8 1/2 in (Standard gauge)
Dimensions and Weights
Length58 ft 0 9/16 in
Wheelbase22 ft 8 in
Fixed wheelbase7 ft 9 in
Total wheelbase48 ft 6 in
Service weight93,350 lbs96,330 lbs
Adhesive weight64,000 lbs65,180 lbs
Total weight153,350 lbs156,330 lbs
Axle load33,100 lbs32,650 lbs
Water capacity2,400 us gal
Fuel capacity12,000 lbs (coal)
Power sourcesteam
Estimated power700 hp (522 kW)
Optimal speed37 mph34 mph
Starting effort12,138 lbf13,313 lbf
Power Plant
Driver diameter68 in62 in
Boiler pressure140 psi
Expansion typesimple
Cylinderstwo, 17 x 24 in
Grate area34.8 sq ft
Firebox area155 sq ft
Tube heating area1,134 sq ft
Evaporative heating area1,289 sq ft
Total heating area1,289 sq ft
Calculated Values
steam locomotive
last changed: 03/2023

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