| Southern Pacific AC-9 | |
|---|---|
| Power type | Steam |
| Builder | Lima Locomotive Works |
| Serial number | 7765–7776 |
| Build date | 1939 |
| Total produced | 12 |
| Configuration | 2-8-8-4 |
| UIC classification | (1′D)D2′ h4 |
| Gauge | 4 ft 8 1⁄2 in (1,435 mm) |
| Driver diameter | 631⁄2 in (1,613 mm) |
| Axle load | 66,400 lb (30.1 tonnes) |
| Weight on drivers | 522,200 lb (236.9 tonnes) |
| Locomotive weight | 677,200 lb (307.2 tonnes) |
| Locomotive & tender combined weight |
998,000 lb (453 t) |
| Fuel type | Coal |
| Fuel capacity | 28 short tons (25 t; 25 long tons) |
| Water capacity | 22,100 US gallons (84,000 l; 18,400 imp gal) |
| Boiler pressure | 250 psi (1.72 MPa) |
| Firegrate area | 139.5 sq ft (12.96 m2) |
| Heating surface: Total |
6,918 sq ft (642.7 m2) |
| Superheater area | 2,831 sq ft (263.0 m2) |
| Cylinders | Four (simple articulated) |
| Cylinder size | 24 × 32 in (610 × 813 mm) |
| Valve gear | Walschaerts |
| Tractive effort | 123,364 lbf (548.75 kN) |
| Career | Southern Pacific Company |
| Number | 3800–3811 |
| Disposition | All scrapped |
The AC-9 was one of two Southern Pacific Railroad'sarticulated steam locomotive class that ran smokebox forward after 1920. Twelve AC-9 class locomotives were built by Lima in 1939 and were Southern Pacific's biggest steam engines. The AC-9s were partially streamlined (the only articulated steam engines to be so equipped), having skyline casings, and were equipped with coal tenders, unlike the cab forwards. Wheel arrangement was 2-8-8-4, nickname "Yellowstone". Between 1939 and 1952, all the twelve AC-9 engines were in service between Tucumcari (New Mexico), El Paso (Texas), and Tucson (Arizona), where they mainly pulled freight trains and occasionally also passenger trains such as the Golden State Limited. In 1952, they were converted to burn oil instead of coal, and moved to the Southern Pacific's "Modoc" line between Sparks (Nevada) and Alturas (California), where they worked in freight service from 1953 till retirement in 1956. There is no preserved AC-9.