NER Class Y [LNER A7]

The NER Class Y, designated LNER A7 after the 1923 Grouping, was a series of three-cylinder simple-expansion 4-6-2 Pacific side-tank locomotives designed by Vincent Raven and built at Darlington Works from 1910, intended for the heavy transfer freight and mineral working on the NER's intensive freight network around Teesside and the Durham coalfields. The A7 was a relatively unusual type in British practice — a Pacific tank locomotive for freight duty rather than the suburban passenger use for which the Pacific tank wheel arrangement was more commonly employed elsewhere — and represented Raven's application of his three-cylinder philosophy to a freight tank locomotive requirement.

Raven designed the Class Y with three cylinders for the same reason he specified three cylinders for the Z Class Atlantics: the smooth, balanced power delivery of the three-cylinder arrangement reduced the hammer-blow on the track and the surging motion that made two-cylinder locomotives difficult to work steadily at the slow, heavy-load speeds of mineral transfer working. The 4-6-2T wheel arrangement gave six coupled wheels for adhesion on the heavy mineral trains and a trailing bogie for stability, while the large side tanks provided water capacity for extended working without the need for a tender.

In service the A7 Class gave competent performance on NER heavy transfer and mineral duties around Teesside, working the movement of iron ore, coke, and pig iron between the various Teesside works and interchange points. The LNER continued them on former-NER transfer freight and mineral duties until progressive withdrawal. None was preserved.