ATSF 3000 class 2-10-10-2. In this photo, the forward section of the boiler appears to be a primitive superheater and feedwater heater.

Santa Fe herald.

ATSF 2-10-10-2 No. 3003 outside Winslow, Arizona, ca. 1913-1914.  Photo by Harold B. Phelps.

ATSF 3000 Class 2-10-10-2 Articulated Steam Locomotive
This class of ten 2-10-10-2 locomotives were actually rebuilt from more conventional 2-10-2 Baldwin-built locomotives by the Atchison, Topeka and Santa Fe Railway in 1911 to 1912.

Although they appeared to have exceedingly long boilers, the barrel in front of the rear set of cylinders actually contained first a primitive firetube superheater for further heating the steam before use; the steam was carried forward from the boiler proper by outside steam pipes as shown in the photograph. Also in this space was a reheater for the high-pressure exhaust before it was fed to the forward low-pressure cylinders.

In front of that, there was a feedwater heater, a space where cold water from the tender could be warmed before being injected into the water proper. This worked similarly to the boiler itself; the firetubes passed through the feedwater tank. The ATSF 2-10-10-2, No. 3000 when built before the others, was the largest locomotive in the world from 1911 to possibly until early 1914.

"The first 2-10-10-2s were constructed in 1911 by the Atchison, Topeka and Santa Fe Railroad at a cost of $43,880 each. They were built out of existing 900 & 1600 class 2-10-2s with new front engines and tenders from Baldwin. They were used between Bakersfield and Barstow and up to San Bernardino. The railroad built 10 of these engines, which were cobbled together by the Santa Fe using existing 2-10-2 engine units united with low-pressure engine units supplied by Baldwin. Baldwin also designed and built the unusual "turtleback" tender that probably was designed to improve rearward vision.

A distinctive ribbed firebox trailed the long boiler. Like other Santa Fe Mallets, the actual tube length was relatively short, but a "reheater" ahead of the forward tube sheet and boiler joint was supposed to maintain steam heat as it traveled forward to the high-pressure cylinders. It added 2,659 sq ft, but was nowhere nearly as efficient as later superheater designs. The design was unsuccessful and the engines were converted back to 2-10-2 simple-expansion locomotives in 1915-1918." 

The experiment was unsuccessful and the locomotives were rebuilt to 2-10-2s during 1915–1918.

Under the Whyte notation for the classification of steam locomotive wheel arrangements, a 2-10-10-2 is a locomotive with two leading wheels, two sets of ten driving wheels, and a pair of trailing wheels.

Other equivalent classifications are:
UIC classification: 1EE1 (also known as German classification and Swiss classification)
Italian and French classification: 150+051
Turkish classification: 56+56
Swiss classification: 5/6+5/6

The equivalent UIC classification is refined to (1′E)E1′ for Mallet locomotives. All 2-10-10-2 locomotives have been articulated locomotives, Mallet locomotives in particular.

This wheel arrangement was rare. Only two classes of 2-10-10-2 locomotives have been built; the Atchison, Topeka and Santa Fe Railway's 3000 class, and the Virginian Railway's class AE.

ATSF 3000 Class Overview

Type and Origin
Power type: Steam
Builder: ATSF (from Baldwin 2-10-2s)
Build date: 1911-1912
Total Produced: 10
Configuration: 2-10-10-2
Gauge: Standard
Road numbers: 3000–3009
Driver diameter: 57 in (1.448 m)
Weight: 616,000 lb (279,400 kg; 279.4 t)
Tender weight: 266,400 lb (120,800 kg; 120.8 t)
Total length: 122 ft (37.19 m)
Overall wheelbase: 108 ft 10 in (33.17 m)
Tractive effort: 111,600 lbf (496 kN)
Boiler pressure: 225 psi (1.55 MPa)
Cylinder diameter: 28 in (711 mm) high pressure, 38 in (965 mm) low pressure
Cylinder stroke: 32 in (813 mm)
Operator: AT&SF
First Run: 1911
Disposition: Rebuilt to 2-10-2s during 1915–1918.

See also:

Virginian AE Class 2-10-10-2 Locomotive

AT&SF Railway

2-10-10-2 Steam Locomotives

Steam Locomotives

The Santa Fe 3000 Articulated Compound Locomotive was once the largest locomotive in the world.
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ATSF 2-10-10-2 No. 3003.
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ATSF 3000 class 2-10-10-2. The forward section of the boiler is actually a primitive superheater and feedwater heater.

The Santa Fe's mighty 2-10-10-2 3000 Class articulated locomotive was once the largest locomotive in the world.

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