LNWR 2-2-2 3020 Cornwall - 1847 Design By Trevithick

1847 Design By Trevithick

Francis Trevithick had a notable pedigree as a locomotive engineer, being the son of Richard. He had moved North to become resident engineer, then Locomotive Superintendent of the Grand Junction Railway (GJR) (later formed into the LNWR). Cornwall was named after the county of his birth.

Cornwall was an attempt to avoid the damaging long wheelbase of the Cramptons, whilst still permitting large driving wheels. By moving the driving axle ahead of the firebox, one of the carrying axles could be moved backwards, giving a shorter overall wheelbase. The difficulty of how to fit the axles past the boiler recurred, to which Trevithick provided an "extremely complicated" solution. The boiler was placed entirely underneath the driving axle. Even then, it was necessary to recess a transverse channel across the top of the boiler, so as to provide clearance for the driving axle. The trailing carrying axle passed through a crosswise tube through the middle of the firebox. This made assembly difficult, but as it was only a straight carrying axle rather than a cranked driving axle, the tube diameter required was manageable. This use of a cross-firebox axle tube was part of Crampton's patent of 1842. As completed in 1847, and first numbered 173, Cornwall was a 4-2-2 with 8' 6" drivers, paired leading wheels of 3' 6", single trailing wheels of 4' and an overall wheelbase of 16' 6". This is the condition in which she was exhibited at The Great Exhibition of 1851.

The Railway Gazette, cited in, suggests that there was an even earlier design for Cornwall, as a 2-2-2 with single 4' wheels both forward and back. It's uncertain if Cornwall was ever built in this form. The drawing does show a considerable front overhang, with a high load placed on the front axle. If constructed like this, the likelihood is that it would suffer the same problems as its contemporary, Gooch's first 2-2-2 Great Western class of 1846, where a broken front axle led to re-design as a 4-2-2.

A typical Crampton feature, previously used on Liverpool, was the large diameter of the outside eccentrics used to drive the valve gear. These were so large as to be larger than the driving cranks, thus avoiding the need for an overhung (and potentially weak) crank. The 17½" × 24" cylinders were horizontal, fed by inclined steam chests above them.