4-4-2+2-4-4

4-4-2+2-4-4 (Double Atlantic)
Diagram of two small leading wheels, two large driving wheels joined by a coupling rod, two small trailing wheels, two large driving wheels joined by a coupling rod, and two small leading wheels
Equivalent classifications
UIC class 2B1+1B2
French class 221+122
Turkish class 25+25
Swiss class 2/5+2/5, 4/10 from the 1920s
Russian class 2-2-1+1-2-2
First known tank engine version
First use 1912
Country Australia
Locomotive TGM M class
Railway Tasmanian Government Railways
Designer Beyer, Peacock and Company
Builder Beyer, Peacock and Company

Under the Whyte notation for the classification of steam locomotives by wheel arrangement, a 4-4-2+2-4-4 is a Garratt articulated locomotive. The wheel arrangement is effectively two 4-4-2 locomotives operating back to back, with each power unit having four leading wheels on two axles in a leading bogie, four powered and coupled driving wheels on two axles, and two trailing wheels on one axle in a trailing truck. Since the 4-4-2 type is usually known as an Atlantic, the corresponding Garratt type is often referred to as a Double Atlantic.

Overview

The 4-4-2+2-4-4 was not a common Garratt wheel arrangement. Only ten were built, all by Beyer, Peacock and Company, the owner of the Garratt patent.[1]

Usage

Argentina

Eight locomotives were built for Argentina to run on 4 ft 8 1⁄2 in (1,435 mm) standard gauge.[1]

After nationalization in 1948, all these locomotives were rostered on the Ferrocarril General Urquiza (FCGU).[1]

Australia

The first Garratt locomotives to be built to the 4-4-2+2-4-4 wheel arrangement were a pair of M class passenger locomotives for the 3 ft 6 in (1,067 mm) gauge Tasmanian Government Railways in Australia in 1912. They were acquired to haul express passenger trains between Launceston and Hobart.[1][2]

The two M class engines were the only eight-cylinder Garratt locomotives in the world. They were difficult to maintain and, despite their haulage abilities and speed, both were withdrawn from service some time after the arrival of the R class 4-6-2 Pacific types in 1924. Both locomotives were scrapped and cut up in the late 1940s.[2]

References

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