A 2-4-6-2 steam locomotive, in the

Whyte notation Whyte notation is a classification method for steam locomotives, and some internal combustion locomotives and electric locomotives, by wheel arrangement. It was devised by Frederick Methvan Whyte, and came into use in the early twentieth cen ...

for describing locomotive

wheel arrangement In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and c ...

s, has a two-wheel

leading truck The leading wheel or leading axle or pilot wheel of a steam locomotive is an unpowered wheel or axle located in front of the driving wheels. The axle or axles of the leading wheels are normally located on a leading truck. Leading wheels are used ...

, one set of four driving wheels, one set of six driving wheels, and a two-wheel

trailing truck On a steam locomotive, a trailing wheel or trailing axle is generally an unpowered wheel or axle ( wheelset) located behind the driving wheels. The axle of the trailing wheels is usually located in a trailing truck. On some large locomotives, ...

. Other equivalent classifications are:

UIC classification The UIC classification of locomotive axle arrangements, sometimes known as the German classification''The Railway Data File''. Leicester: Silverdale, 2000. p. 52. . or German system,Kalla-Bishop P.M. & Greggio, Luciano, ''Steam Locomotives'', Cre ...

: 1BC1 (also known as German classification and

Italian classification The UIC classification of locomotive axle arrangements, sometimes known as the German classification''The Railway Data File''. Leicester: Silverdale, 2000. p. 52. . or German system,Kalla-Bishop P.M. & Greggio, Luciano, ''Steam Locomotives'', Cre ...

)

French classification Under the French classification system for locomotive wheel arrangements, the system is slightly different for steam and electric/diesel vehicles. Steam The French system counts axles, rather than wheels. As with Whyte notation, a conventional r ...

: 1231

This most unusual wheel arrangement was only ever used on the , a French

duplex locomotive A duplex locomotive is a steam locomotive that divides the driving force on its wheels by using two pairs of cylinders rigidly mounted to a single locomotive frame; it is not an articulated locomotive. The concept was first used in France in 1 ...

type built in 1932 for the PLM. Although a rigid locomotive, not articulated, it had some similarities to a Mallet as it was a

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struc ...

with the two groups of drivers driven by the high pressure cylinders for the rear 6-coupled group and the low pressure for the front 4-coupled group. As the two groups of drivers were also linked with inside

coupling rod A coupling rod or side rod connects the driving wheels of a locomotive. Steam locomotives in particular usually have them, but some diesel and electric locomotives, especially older ones and shunters, also have them. The coupling rods transfer t ...

s through inside cranks on the second and third drivers,

André Chapelon André Chapelon (26 October 1892 – 22 July 1978) was a French mechanical engineer and designer of advanced steam locomotives. A graduate engineer of Ecole Centrale Paris, he was one of very few locomotive designers who brought a rigorous scien ...

considered that this made the locomotive a

2-10-2 Under the Whyte notation for the classification of steam locomotives, represents the wheel arrangement of two leading wheels, ten powered and coupled driving wheels, and two trailing wheels. In the United States of America and elsewhere the is ...

rather than a duplex, which was also consistent with the PLM numbering as 151. Linking the drivers did not transfer appreciable power between them, but it did keep them synchronised in phase, so that the pistons moved as a balanced locomotive. Power from each pair of cylinders was balanced in the ratio 2:3 to distribute power equally across each wheelset. The

compound locomotive A compound locomotive is a steam locomotive which is powered by a compound engine, a type of steam engine where steam is expanded in two or more stages. The locomotive was only one application of compounding. Two and three stages were used in shi ...

s were built to haul heavy freight trains on the 0.8%

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

of the

Paris–Marseille railway The railway from Paris to Marseille is an 862-kilometre long railway line, that connects Paris to the southern port city of Marseille, France, via Dijon and Lyon. The railway was opened in several stages between 1847 and 1856, when the final secti ...

between Les Laumes and

Dijon Dijon (, , ) (dated) * it, Digione * la, Diviō or * lmo, Digion is the prefecture of the Côte-d'Or department and of the Bourgogne-Franche-Comté region in northeastern France. the commune had a population of 156,920. The earlies ...

. Their performance was so good that the company wanted to order more engines, but the nationalization of the French railways in 1938 stopped all projects. These duplex engines were fitted with Lenz-Dabeg rotary cam valve gear and soon thereafter with

double chimney A double chimney (or double stack, double smokestack in American English) is a form of chimney for a steam locomotive, where the conventional single opening is duplicated, together with the blastpipe beneath it. Although the internal openings form ...

s. The driving wheels had a diameter of . The highest permissible speed was . In a test on 19 December 1933, the engine developed slightly more than at the drawbar over a distance of and a speed of at least , without being overworked. In ordinary service these engines could haul , sustaining at the summit of the 0.8% Blaisy grade. After

electrification Electrification is the process of powering by electricity and, in many contexts, the introduction of such power by changing over from an earlier power source. The broad meaning of the term, such as in the history of technology, economic histor ...

of the line, the 151A's were sent for service in northeastern France. They were withdrawn from service in 1956 and scrapped.

References

{{Whyte types 46,2-4-6-2 Railway locomotives introduced in 1932