2-10-10-2

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

ATSF 3000 class 2-10-10-2. The forward section of the boiler is actually a primitive superheater and feedwater heater.

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.

Although they appeared to have exceedingly long boilers, the barrel in front of the rear set of cylinders actually contained first a primitive 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 contained in this space was a reheater to give additional energy to 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 experiment was decidedly unsuccessful, and the locomotives were rebuilt back to 2-10-2s during 1915–1918.

Specifications

• Road numbers: 3000–3009
• Driver diameter: 57 in (1.4 m)
• Weight: 616,000 lb (279,400 kg = 279.4 t)
• Tractive effort: 111,600 lbf (496 kN)
• Boiler pressure: 225 psi (1.55 MPa)
• Cylinder diameter: 28 in (710 mm) high pressure, 38 in (970 mm) low pressure
• Cylinder stroke: 32 in (810 mm)

Virginian Railway class AE

Virginian Class AE
Virginian Class AE
Power type	Steam
Reference:
Builder	American Locomotive Company
Build date	1918
Total produced	10
Configuration	2-10-10-2
Gauge	1,435 mm (4 ft 8 1⁄2 in)
Driver diameter	56 in (1,422 mm)
Wheelbase	64.3 ft (20 m)
Width	12.0 ft (4 m)
Height	16.7 ft (5 m)
Weight on drivers	617,000 lb (280 t)
Locomotive weight	684,000 lb (310 t)
Tender weight	214,300 lb (97 t)
Locomotive & tender combined weight	898,300 lb (407 t)
Fuel type	Coal
Water capacity	13,000 US gal (49,210 l)
Tender capacity	12 tons (11 t)
Boiler	119 in (3,023 mm)
Boiler pressure	215 psi (1 MPa)
Firegrate area	109 sq ft (10 m2)
Heating surface: Total	8,606 sq ft (800 m2)
Superheater area	2,120 sq ft (197 m2)
Cylinders	4
Front cylinder size	48 × 32 in (1,219 × 813 mm)
Rear cylinder size	30 × 32 in (762 × 813 mm)
Tractive effort	Compound: 147,200 lbf (655 kN) Simple: 175,000 lbf (778 kN)
Factor of adhesion	4.2
Locomotive brakes	Air
Train brakes	Air
Career	Virginian
Number in class	10
Number	800-809
Disposition	scrapped

This class of ten locomotives were built in 1918 by ALCO for the Virginian Railway. While suffering from the horsepower limitation of Mallets, which limited their speed, the locomotives had the highest tractive effort of any steam locomotives ever built. Due to size limitations en route, they were delivered without their cabs and the front, low pressure cylinders, which were installed on site. The low pressure cylinders and the boiler were both the largest diameter ever used on a US locomotive; the cylinders had to be tilted slightly upward to provide sufficient clearance.

As can be seen in the photograph, the tenders fitted were unusually small; this so that they could use the Virginian's existing turntables.

This class were true Mallet locomotives, in that as well as being articulated between the forward, swinging engine unit and the rear fixed one, they were also compound locomotives; the rear, high pressure cylinders exhausted their steam via a long pipe into the huge front cylinders. Like many compound locomotives, they could be operated in simple mode for starting; high pressure steam could be sent straight to the front cylinders at low speed, for additional tractive effort.

Unlike some other giant locomotives of the period, the immense boilers could generate enough steam to make them a success on the slow (8 mph or 13 km/h) coal trains for which they were built. They remained in service until the railroad electrified in 1952 and could be considered the ultimate drag era locomotive.