How To Articulate "Locomotive".

Updated: 19 Apr 2008

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As the requirement for power increases, locomotives get longer and heavier. Soon a fixed wheelbase becomes too long to get round corners, and some sort of hinge or articulation is needed. Here are the main ways of doing it:

The Mallet Configuration.

The boiler is rigidly fixed to the rear powered unit. The front engine unit pivots on the rear one, and a sliding bearing takes the weight of the forward part of the boiler.

This does not at first appear to be the best way to articulate a loco as the front end of the boiler, being fixed to the rear wheels, sticks out on curves. However it was very popular and successful in the USA

The Meyer Configuration.

Here the boiler is pivoted to BOTH engine units, rather than one, and so the boiler sticks out a lot less than in the Mallet version.

For a very compact example see: The Hunslet geared locomotive.

The Garratt Configuration.

This is similar to the Meyer, except that the boiler is slung between the two engine units instead of sitting on top of them. This allows the boiler to be mounted lower, so it can have a greater diameter and a bigger firebox, and still stay within the loading gauge.

The Beyer-Garratts were successfully used all over the world; almost the only place they were never adopted was the USA.

Left: an East African Railways Garratt

The engine unit to the left carries the tender, while the front engine unit on the right carries a large water tank. I once stood on the footplate of one of these machines while it was rusting away in a siding at Durban docks. So there.

All of the types listed above had considerable commercial success, and cannot be classed as "unusual". However, these articulation schemes will be met with in locomotives that had other claims to fame, such as The Flexible Mallets of the USA.

There were other less popular ways to articulate, such as:

The Du Bousquet Configuration

These French locomotives were designed for severe gradients on the Paris ceinture and elsewhere.

A model Du Bousquet locomotive.

This beautiful model is in CNAM. (The Paris Science Museum)

Author's photo. The picture quality is not all it might be but you cannot use flash, and have to take the photograph through plate glass.

For more info see: The du Bousquet page.

The Golw Configuration

These French-built designs were used with success in Africa, but never had a wide following. The front engine unit swivelled under the boiler in a similar manner to a Meyer locomotive; in contrast a Garratt had its front bogie in front of the boiler. The rear engine unit was placed underneath the tender, in a manner similar to a Garratt; however a Garratt carried its coal and water directly on the rear bogie, while the Golw carried them on the central frame. The rear bogie cylinders were placed under the cab, at the front of the rear unit. A float-controlled automatic device reduced the cut-off of the rear cylinders to prevent slipping when the water tank was running low; this precaution was not required on the front bogie because there were no water tanks at the front, and the boiler would always be more or less full of water. The firebox hung low between the two engine units, and so could be of generous size.

Four locomotives with a 2-6 + 6-2 configuration were supplied to the Ivory Coast railways in 1930, and three more to the Congo-Ocean Railway in what was then the French Congo. (Now The Republic of the Congo) The Congo-Ocean railway received two more of the same type in 1935 and five of a modified 2-6-6-4 configuration. These repeat orders suggest the locomotives were successful, but both railways later adopted the Garratt type.

A Golw locomotive.

This design was used in the Ivory Coast.

Weight empty: 68,400 kg
Service weight: 87,700 kg
Adhesion weight: 73,00 kg

Image courtesy Claude Bersano

More material on these other types of articulation will be published when I finally locate a Round Tuit.


Books on Articulated Locomotives:

"Articulated Locomotives of North America" by Robert A LeMassena. Sundance Books 1979. At least 2 volumes.
This is a most impressive work. Long out of print, I fear. I have only ever seen Vol 1, and I don't know how many volumes there are in total.

"Articulated Locomotives" by Lionel Wiener. A classic on the subject.

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