A booster motor can be added to a steam locomotive to drive the trailing wheels for extra traction and power. They were most widely used in the US and Australia on steep or hilly lines, but were not universally used due to the extra cost and complexity. The steam supply and mechanical connection required for a booster engine could be quite complex. Some locomotives without trailing wheels used a brace on the front wheels of the tender.
A booster motor is a component that can be added to a steam locomotive to drive the trailing wheels. Most steam locomotives have one or more sets of wheels that are only there to provide extra stability at high speeds. These wheels can be used for extra traction and power when the locomotive first starts moving if a booster motor is added. The booster engine usually consists of a two-cylinder steam engine that is powered by the same steam as the rest of the locomotive. After the locomotive reaches a particular speed, booster motors are usually designed to disengage so that the sprockets spin freely.
Booster engines were not universally used throughout the world, as there was some disagreement as to whether the extra cost was justified. These devices were most widely used in the United States and Australia, although there were many lines in those countries that did not use them either. Several lines in Canada and New Zealand also used booster engines. In many cases, a boost was intended to provide additional power on steep or hilly lines.
In most cases, the booster motor would be installed in the running gear of a locomotive behind the trailing wheels. These devices were installed after the locomotive was built, so they tended to add additional cost and complexity. To operate, they required access to boiler steam and a mechanical connection to a drag shaft.
The steam supply for a booster engine could be quite complex, including a variety of check valves, shut-off valves, and chokes. Boosters usually had their own dedicated pressure gauge and lubrication system, which could also add to the complexity of the system. To connect the booster motor to the shaft, one or two rockers were used. One of these devices would allow the amplifier to run in the forward direction, and a second would be used if it were a reversible unit. Additional mechanisms could automatically disable the boost after reaching a particular speed.
On some locomotives that lacked trailing wheels, a brace would be fitted to the front wheels of the tender. This setup was also sometimes used for switching locomotives, in which case the tender’s driving wheels could be connected to the other wheels with tie rods. Short tie rods like these were speed restricted, which was not a concern for changing locomotives that were confined to rail yards.
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