Booster Locomotives

Gallery opened: 13 Feb 2021

Updated: 28 Feb 2021

Franklin booster added
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The term "booster locomotive" covers a wide range of machinery all using the same basic principle- an extra set of small wheels and cylinders to provide extra tractive effort at low speeds, such as when starting, or on heavy gradients. This machinery was often mounted on the tender, or in some cases attached to the loco under the cab. In a few instances the additional small driving wheels were squeezed in between the main drivers and a leading bogie.

There were designs that had an extra drive system under the tender, intended for continuous use rather than just at starting- for example Sturrock's steam tenders, and the American Triplexes; these are not considered to be "booster" locomotives, though obviously they are closely related; the difference is a booster is working onlt for short periods, usually on starting, while a steam tender is always in use.

Booster engines have a good Wikipedia page.


Left: Type AA-1 Nr.1400 Steam Locomotive: 1896

This unique locomotive only had one pair of main driving wheels, but the design squeezed in a small booster pair of driving wheels between the conventional front bogie and the main drivers; they were normally held off 1.25 inches above the track by springs, but extra tractive effort was required the wheels were pressed down on the rails by a steam cylinder. This axle was powered by two small cylinders under the main cylinders, working completely independently.

It was built by Krauss in 1896, and was designed by their Chief Mechanical Engineer Richard von Helmholtz, for operation on the Royal Bavarian State Railways.

It appears that the auxilary axle is here in the lifted position.

No 1400 has a short Wikipedia page.

Left: Type AA-1 Nr.1400 Steam Locomotive: 1896

This photograph appears to have been taken at the same time as that above. Note similarity of background and puddles. The auxilary axle is here in the lifted position.

You might think that such a complicated arrangement was asking for trouble, but it appears that 1400 ran successfully and economically for several years. In 1907 she was involved in an accident and was rebuilt as a conventional locomotive. Also the design was never repeated, so one must assume that ultimately it was not a good idea. The rebuilt engine was the last Bavarian 4-4-0 locomotive to be retired, in 1933.

The Whyte system classifies it as a 4-2-2-2 tender locomotive.

Left: Type AA-1 Nr.1400 Steam Locomotive: 1896

This is a different reproduction of the image above, retouched to remove the local scenery.

Left: Micro-Metakit 91001H model of Nr.1400 Steam Locomotive

It seems that Micro-Metakit make models of almost everything. They are precision museum-quality models, cost some £3000 each.

It is not known if the model incorporates a lifting mechanism for the booster axle.

Left: Micro-Metakit 91001H model of Nr.1400 Steam Locomotive

The other side of the model.


Left: P3.II, “Dr. von Clemm “Royal Bavarian State Railroad

This locomotive was built on the "System von Clemm" in 1900 by Krauss. It was designed for express service in Bavaria. It had a most unusual wheel arrangement of 6-4-2. Two modestly-sized cylinders at the front drove the central axle of the six-wheel front bogie; a close examination of the photograph shows that the central bogie wheel is lifted off the rail, presumably by a mechanism like that of No 1400 above. It is believed that the front driving wheels were only used for starting. Two larger pistons in the rectangular box just ahead of the cab drove the four central wheels.

The locomotive was painted in dark blue, gray, and black with gold lining and was provided with an eight wheel tender for the 1900 Paris World Exhibition, where it won a gold medal. At this point it had a Westinghouse air pump.

Left: P3.II, “Dr. von Clemm “Royal Bavarian State Railroad

By 1902 the locomotive had been given a 3-axle tender 3T16, and repainted in purple-violet, black,and red with red lining. At this point it had a Schleifer air pump.

The board on the side of the boiler says "Paris World Exhibition" in German.


Boosters were popular and highly successful in the USA, and were also used to a lesser extent in Canada and Great Britain.

Left: Franklin booster bogie

Franklin was one of the major American companies making booster systems. They produced 4-wheel booster bogies to fit under tenders, and 2-wheel units to fit under the cab of the locomotive.

The two steam cylinders are at left with the valve-chest between them. At right is the driven axle.

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