Southern Pacific classes AC-7, AC-8 and AC-10 to AC-12
United States 1937 143 produced
After the AC-6 class cab forwards, 26 slightly larger AC-7 class locomotives were built in 1937. They were technically almost identical to their predecessors and differed visually in that they had a larger tender and a cab that was sloped at the front. The two frames of the locomotives were now cast together with the cylinders in one piece each. These were followed by 27 almost identical AC-8, 40 AC-10, 30 AC-11 and 20 AC-12. The last AC-12 was also the last steam locomotive to be built for the Southern Pacific. These five subclasses were retired between 1954 and 1959.
Technical data
General
| Property | AC-7, AC-8 | AC-10 to AC-12 |
|---|---|---|
| Built | 1937, 1939 | 1942-1944 |
| Manufacturers | Baldwin | |
| Wheel arrangement | 4-8-8-2 | |
| Gauge | 1,435 mm (Standard gauge) | |
Dimensions and weights
| Property | AC-7, AC-8 | AC-10 to AC-12 |
|---|---|---|
| Wheelbase | 20.37 m | 20.50 m |
| Service mass | 290.2 t | 298.4 t |
| Adhesion mass | 233.5 t | 241.2 t |
| Total mass | 424 t | 443.6 t |
| Rigid wheelbase | 5.13 m | |
| Axle load | 30.4 t | 31.3 t |
| Water capacity | 83,279 l | |
| Fuel capacity | 24,227 l (oil) | 23,091 l (oil) |
| Total wheelbase | 34.19 m | |
Boiler
| Property | AC-7, AC-8 | AC-10 to AC-12 |
|---|---|---|
| Grate area | 12.914 m² | |
| Firebox surface | 47.659 m² | 44.408 m² |
| Tube heating surface | 556.676 m² | |
| Evaporative heating surface | 604.335 m² | 601.084 m² |
| Superheater surface | 277.595 m² | 242.942 m² |
| Total heating surface | 881.9 m² | 844.0 m² |
Power plant
| Property | AC-7, AC-8 | AC-10 to AC-12 |
|---|---|---|
| Driver diameter | 1,613 mm | |
| Boiler pressure | 17.2 bar | |
| Expansion type | simple expansion | |
| Cylinders | four, 610 x 813 mm | |
Power
| Property | AC-7, AC-8 | AC-10 to AC-12 |
|---|---|---|
| Power source | steam | |
| Indicated power | 4,474 kW (6,083 PS) | |
| Starting effort | 548.8 kN | |
Calculated values
| Property | AC-7, AC-8 | AC-10 to AC-12 |
|---|---|---|
| Factor of adhesion | 1 : 4.17 | 1 : 4.31 |
| Optimal speed | 50 km/h | |
| Power-to-weight ratio | 15.4 kW/t | 15.0 kW/t |
| Heating Surface Equivalent | 1,397.8 m² | 1,309.0 m² |
| Cylinder volume/HSE | 1 : 678.85 | 1 : 724.91 |
| Adhesive weight/Total | 1 : 1.24 | |
| Tractive force/Heating surface | 1 : 13.00 | 1 : 13.58 |
| Grate area/Heating surface | 1 : 68.29 | 1 : 65.36 |
| Firebox/Tube surface | 1 : 11.68 | 1 : 12.54 |
| Total/Superheater | 1 : 2.18 | 1 : 2.47 |
