Garratt locomotive

A Garratt locomotive is a type of three-part articulated steam locomotive invented by the engineer Herbert William Garratt. Its boiler, firebox, and cab are mounted on a centre frame or "bridge". The two other parts, one at each end, have a pivot to support the central frame; they consist of a steam engine unit – with driving wheels, trailing wheels, valve gear, and cylinders, and above it, fuel and/or water storage.

Articulation permits locomotives to negotiate curves that might restrict large rigid-framed locomotives. The design also provides more driving wheels per unit of locomotive weight, permitting operation on lightly engineered track. Garratt locomotives produced as much as twice the tractive effort of the largest conventional locomotives of railways that introduced them, reducing the need for multiple locomotives and crews. Provided by Wikipedia