Mallet locomotive

Mallet locomotive
A typical European Mallet type, a narrow gauge 0-4-4-2 tank locomotive for a mountain railway (in this case, the RhB G 2/2+2/3 in Switzerland).
A 2-10-10-2 Mallet Locomotive in Winslow, Arizona, during 1913-14.
A 2-6-6-2 Mallet Locomotive at the Northwest Railway Museum in Snoqualmie, Washington
A preserved 2-6-6-2T Mallet
Diagram of Mallet articulation system
Portuguese Railways Mallet locomotive No. E168 at Povoa da Varzim, August 1970
Swedish built Mallet locomotive DONJ No 12 in Jädraås, Sweden, August 2009

The Mallet Locomotive is a type of articulated locomotive, invented by a Swiss engineer named Anatole Mallet (and thus, the name is properly pronounced in the French manner, "Mallay").

The Mallet locomotive has two "engines"-- i.e. two pairs of cylinders, each pair rod-connected to a group of driving wheels. The axles of the rear set of drivers turn in the main frame of the locomotive, which is fixed to the boiler above it (at the rear end, to allow expansion of the hot boiler). The frame holding the front set of drivers is hinged to the main frame, allowing it to swing from side to side. The front end of the boiler rests on a sliding bearing on the swinging front frame.


Compound expansion

Mallet's original design was a compound locomotive, in which the steam is used twice, first in a set of high-pressure cylinders, then in a set of low-pressure cylinders. This confers certain thermodynamic advantages, and also worked well with the Mallet design. Steam was fed from the steam dome down to the aft, high-pressure cylinders — the exhaust steam from those being fed forwards in a pipe with a swiveling joint — to the forward, low-pressure cylinders. The exhaust steam from the larger low-pressure cylinders is exhausted through a slit in the sliding bearing in the top of the swiveling truck and thus to the smokebox above, and the blastpipe (US: exhaust nozzle) and chimney (US: stack). The difference in size between the high and low pressure cylinders can be seen in the picture of the 2-6-6-2 Mallet.

Unlike the case of the rigidly-framed locomotive, the Mallet design is easier to build as a compound, since steam and exhaust pipes are needed for both pairs of cylinders when it is built as a simple. When built as a compound, the only flexible pipes that are needed are the ones that deliver low-pressure steam from the rear cylinders to the front.

Simple expansion

Mallet's original patent specifies compound expansion, but after his death in 1919 many locomotives (particularly in the United States) were articulated Mallet style without using compounding (for instance the Union Pacific Big Boy). When fleets of such locomotives appeared in the middle 1920s the trade press naturally called them "Simple Mallets" — i.e., simple locomotives articulated like Mallets — but eventually the notion spread that this was somehow incorrect. The term "Mallet" continued to be widely used for simples as well as compounds, but enthusiasts who like to consider themselves purists insist "simple Mallet" is an oxymoron.[1]


Mallet's original design was intended to allow a medium-size locomotive to better negotiate the tight curves of a narrow gauge railway, but the design was particularly attractive to railroads in the United States because it permitted locomotives to be built to sizes impossible with a single, rigid frame. It was introduced to the USA by the Baltimore & Ohio Railroad in 1904.[2] The 4-8-8-4 "Big Boy" used by Union Pacific Railroad and the 2-6-6-6 Allegheny of the Chesapeake and Ohio Railway were the heaviest steam locomotives in the world; the 2-8-8-2 Y6b class of the Norfolk and Western Railway was considered the ultimate development of the Mallet compound locomotive. These engines were built through World War II, with the last Y6b being constructed in 1952. However, outside North America, the Mallet type had generally been superseded by the Garratt locomotive by the mid 1920s, although in the Dutch East Indies, now the Republic of Indonesia, several types and sizes remained in use into the 1980s, and after Indonesian independence in 1949 the Indonesian State railways DKA ordered a series of 0-4-4-2's, basically an updated version of the earlier Dutch design, in 1962, destined for the old Atjeh (now Aceh) tramway. Constructed by Nippon Sharyo in Japan, these are the only Mallets built in Asia. In contrast to the rest of the Indonesian railways it has a gauge of 750 mm (2'6"), as to 1067 mm (3"6") for the rest of the Archipelago. Smaller Mallets were used by plantations and other industries, all of the 0-4-4-0 type. These ran mostly on 600 mm (1' 11.5") and 700 mm (2' 3.5") gauge networks.


Several Mallets have been preserved, some even in operational condition. A number of the Union Pacific "Big Boys" have escaped the scrapper, including one overlooking the US city of Omaha, where UP is based. One of the early Indonesian Mallets (formally a Dutch colony) has been returned to the Netherlands and is now part of a setup in the Dutch National Railway Museum (Nederlands Spoorweg Museum, NSM), while another industrial type has been purchased and restored by the Statfold Barn Railway in the UK. This will see its first operations in Europe in 2011 and after initial trials on the owners railway, will be transferred to the Ffestiniog and Welsh Highland Railways as its power is better suited to that railway.


  1. ^ "A Big Boy is Not a Mallet". Retrieved September 15, 2009. 
  2. ^ Ransome-Wallis, P. (1959). Illustrated Encyclopedia of World Railway Locomotives (2001 republication ed.). Dover Publications, Inc. pp. 500-501. ISBN 0-486-41247-4. 

External links

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Locomotive Mallet — Locomotive articulée Mallet 020 020, des chemins de fer suisses Une « Locomotives Mallet » est l appellation courante donnée à une locomotive à vapeur articulée compound, système breveté en 1884 par l ingénieur franco suisse Anatole… …   Wikipédia en Français

  • Mallet (disambiguation) — Mallet may refer to: Mallet, a hand tool for striking Mallet (crater), a moon feature Mallet locomotive, a steam locomotive Mallet Assembly, an honors program Mallet (software project), a collection of java code for natural language processing… …   Wikipedia

  • locomotive type Mallet — ● locomotive type Mallet Locomotive à vapeur comportant un châssis principal avec un train de roues motrices et un châssis secondaire articulé sur le premier, possédant un train de roues motrices et, éventuellement, des bogies et bissels porteurs …   Encyclopédie Universelle

  • Mallet (locomotora) — Una locomotora tanque Mallet 0 4 4 0 europea típica, de trocha angosta, para ferrocarriles de montaña (en este caso, el Ferrocarril Rético (RhB) en Suiza) …   Wikipedia Español

  • Locomotive compound — Pour les articles homonymes, voir Compound. Une locomotive compound est une locomotive à vapeur dont la vapeur est réutilisée après une première utilisation. Il y a recyclage, donc économie. Ainsi, le moteur comporte plusieurs étages de cylindres …   Wikipédia en Français

  • Locomotive frame — A locomotive frame is the structure that forms the backbone of the railway locomotive, giving it strength and supporting the superstructure elements such as a cab, boiler or bodywork. The vast majority of locomotives have had a frame structure of …   Wikipedia

  • Locomotive Compound — Pour les articles homonymes, voir Compound. Une Locomotive compound est une locomotive à vapeur dont la vapeur est réutilisé après une première utilisation. Il y a recyclage, donc économie. Ainsi, le moteur comporte plusieurs étages de cylindres …   Wikipédia en Français

  • Locomotive a vapeur — Locomotive à vapeur Consolidation n°4193 du réseau du Nord Les premières locomotives (au XIXe siècle) étaient propulsées par une machine à vapeur, ce qui leur a valu le nom de locomotives à vapeur. Ce type de traction des trains est resté… …   Wikipédia en Français

  • Locomotive À Vapeur — Consolidation n°4193 du réseau du Nord Les premières locomotives (au XIXe siècle) étaient propulsées par une machine à vapeur, ce qui leur a valu le nom de locomotives à vapeur. Ce type de traction des trains est resté largement prépondérant …   Wikipédia en Français

  • Locomotive Articulée — 3 types de locomotives 030+030: l articulation est figurée en rouge Une locomotive articulée est une locomotive dont tous les essieux moteurs ne sont pas dépendants du même châssis. La nécessité de disposer d une puissance suffisante même sur des …   Wikipédia en Français

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.