0-2-2T

An 0-2-2, in the Whyte notation for the classification of steam locomotives by wheel arrangement, is one that has two coupled driving wheels followed by two trailing wheels, with no leading wheels. The configuration was briefly built by Robert Stephenson and Company for the Liverpool and Manchester Railway

Other equivalent classifications are:

The 0-2-2 or Northumbrian wheel arrangement was first used for Stephenson's Rocket, their entry for the Rainhill Trials of 1829, a competition to choose a locomotive design for the new Liverpool & Manchester Railway. Stephenson recognised that the rules of the competition favoured a fast, light locomotive of only moderate hauling power. Although George Stephenson's previous designs had been heavy four-coupled freight locomotives, Rocket was almost entirely new. Stephenson was an advocate of the adhesion railway, against the fashion of the time, and believed that the light loads for Rainhill would even allow just a single driving axle. This allowed the simplification of not requiring either a chain drive between the axles or Stephenson's invention of the external coupling rods.

Achieving adequate traction required more of Rocket's weight to be over the driving axle than the carrying axle. The heavy boiler was placed forwards, with the axle beneath it, giving a 0-2-2 layout rather than 2-2-0. The cylinders were set at a steep angle, as used the year before for Lancashire Witch, rather than the typical vertical cylinders of this period. The cylinders were thus over the firebox and both driver and fireman shared a footplate at the same, rear, end of the engine. Previously they had often been separated to their own ends of the engine.

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