LNWR 2-2-2 3020 Cornwall

LNWR Cornwall
Numbered 3020 in 1886, Cornwall rebuilt as a 2-2-2
Type and origin Power type Steam Designer Francis Trevithick   (son of Richard Trevithick), rebuilt by Ramsbottom Builder LNWR Crewe Build date 1847, rebuilt in 1858 Total produced 1 Rebuild date 1858
Specifications Configuration: ​  • Whyte 4-2-2 rebuilt as 2-2-2 Gauge 4 ft 8 1⁄2 in (1,435 mm) Leading dia. 3 ft 6 in (1.067 m) Driver dia. 8 ft 6 in (2.591 m) Fuel type Coal Water cap 1,800 imp gal (8,200 l; 2,200 US gal) Cylinders Two, outside Cylinder size 17.5 in × 24 in (444 mm × 610 mm), later 17.25 in × 24 in (438 mm × 610 mm)
Performance figures Tractive effort 8,575 lbf (38.1 kN)
Career Operators London and North Western Railway Locale Great Britain First run 1847 Withdrawn 1902 Disposition Used for departmental duties, now preserved.

London & North Western Railway 2-2-2 No. 3020 Cornwall is a preserved steam locomotive. She was built at Crewe in 1847. She was originally a 4-2-2 in 1847, but was extensively rebuilt, and converted to a 2-2-2 in 1858.

In the 1840s, express passenger locomotive design was focussed on the need for single large-diameter driving wheels of around 8 ft (2.4 m). The wheel diameter is effectively the "gear ratio" of a steam engine, and large driving wheels delivered the high linear tyre speed needed for fast locomotives, whilst keeping the axle bearing and piston speeds low enough to remain within the limits of the existing technology. Later on, increasing engine power would require better adhesion than a single pair of driving wheels could provide, but that was not a problem at the time.

As well as needing large wheels for speed, stability required a low centre of gravity, and thus a low-slung boiler. The difficulty was that the two conditions were in conflict, because the boiler of the locomotive would take up the space also needed for the driving axle.

One solution to the problem was the Crampton design, in which the driving axle was moved behind the boiler's firebox. These engines were relatively long in comparison to their contemporaries, and had long rigid frames, sometimes with as many as three carrying axles ahead of the driving axle, creating a 6-2-0 wheel arrangement. Cramptons were most popular in France and Germany, but some were also used in England, by companies including the London & North Western Railway (LNWR).

One of these LNWR Cramptons, Liverpool, was particularly long, having a rigid wheelbase of 18 ft 6 in (6 m). Although the locomotive was fast, and capable of working heavy trains for long distances, its long rigid frame caused damage to the track.

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.