Booster engine

There were variations built by the Franklin company which utilized side rods to transmit tractive force to all axles of the booster truck.

[2] A booster engine is used to start a heavy train or maintain low speed under demanding conditions.

Such small side-rods restrict speed and are therefore confined mostly to switching locomotives, often used in transfer services between yards.

Additionally, the "gearing" of a steam locomotive is fixed, because the pistons are linked directly to the wheels via rods and cranks.

The increased starting tractive effort provided by the booster meant that, in some instances, railroads were able to reduce the number of, or eliminate the use of additional helper locomotives on heavier trains.

This resulted in lower operating and maintenance costs, higher locomotive availability and productivity (ton-miles), and ultimately, greater profitability.

The New York Central was the first railroad to use a booster in 1919 and remained a proponent of the device, applying them to all of its high-drivered 4-6-4 Hudson locomotives to increase their acceleration out of stations with crack passenger trains.

Similarly, the Chesapeake & Ohio specified boosters on all of its Superpower locomotives aside from the Allegheny to increase tonnage ratings over some of the hilly terrain found on their main lines, while rival Norfolk & Western experimented with boosters briefly and found their cost unjustified, instead choosing to increase engine tractive effort through the raising of boiler pressure.

Canadian Pacific Railway rostered 3,257 steam locomotives acquired between 1881 and 1949, yet only 55 were equipped with boosters.

From 1929 onwards, South Australian Railways 500 class 4-8-2 heavy passenger locomotives were rebuilt into 4-8-4s with the addition of a booster truck .

In Great Britain, eight locomotives of four different classes on the London and North Eastern Railway were equipped with booster units by Nigel Gresley.

[8] An early type of booster used in Great Britain was the steam tender, which was tried in 1859 by Benjamin Connor of the Caledonian Railway on four 2-4-0 locomotives.