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Alexander Allan (1809-1891), locomotive engineer,
The 'Crewe' type locomotive.
Worked at Grand Junction Railway works at Crewe, which opened in 1843.
He was one of the original members of the Institution of Mechanical Engineers, which was founded in 1847.
In 1847 he patented a hydrostatic turntable.
1853. He left Crewe to become locomotive superintendent of the Scottish Central Railway.
He later took management of the Worcester Engine Works Co.
He designed the straight-link motion and the air spring pressure gauge and a steam brake. He was also the inventor of improved duplex spring buffers and of a railway carriage roof lamp. 
1891 Obituary 
ALEXANDER ALLAN was born at Montrose in 1809.
After serving his apprenticeship to Mr. Gibb, millwright, at Lochside, near Montrose, he went in 1832 to Messrs. Robert Stephenson's, Newcastle-on-Tyne, and from there to Liverpool.
In 1834 at the Vauxhall Foundry he assisted in putting upon the Liverpool and Manchester Railway Messrs. Forrester's first locomotive, the "Swiftsure," with its novel outside cylinders; and in the same year he was sent to Ireland with their three locomotives, which were the first introduced on the earliest of Irish railways, the Dublin and Kingstown.
In 1840 he entered the service of the Grand Junction Railway Company at Liverpool, and later at Crewe as works manager and assistant locomotive superintendent, Mr. Francis Trevithick being the locomotive superintendent.
At the new works at Crewe he was entrusted with the designing and construction of passenger and goods engines. In these original Crewe locomotives the outside cylinders were so arranged as to simplify the machinery; a straight axle having only two bearings, instead of a crank axle having four, allowed the boiler to be lowered; the size of crank pins and block crossheads was reduced; lighter connecting rods were adopted; and instead of eight slide-bars, as on all other engines at that time, four were used.
In 1847 the "Velocipede" was built on the same design, but with 7 feet driving wheels; and this and other locomotives of similar dimensions were in use on the northern division of the London and North Western Railway until found too small for the increased traffic. The straight-axle locomotive was adopted by Mr. Joseph Locke in 1843 on the London and South Western and on the Paris and Rouen Railway.
In 1846 the Caledonian Railway was supplied with designs by Mr. Allan; and in later years the Scottish Central Railway.
In 1853 he left Crewe to be superintendent of the locomotive department of the Scottish Central Railway, extending to Perth, Aberdeen, Edinburgh, and Glasgow; and filled that post until 1865, when the line was amalgamated with the Caledonian.
In 1854 he invented his straight-link valve-gear, in which balance weights and springs are dispensed with (Proceedings 1856, page 70); the gear requires less room, allowing the boiler to be placed lower; and during reversal the valve rod moves through one-third the space upwards and downwards, compared with the previous valve-gear.
Between 1847 and 1885 he also introduced improvements in turntables; in tubular and locomotive and other boilers; in gas meters (Proceedings 1860, page 15); in locomotive retarding and stopping (1859, page 230); in buffer and draw springs; in land and sea batteries; and air-spring pressure-gauges (1859, page 179).
For several years he was manager of the Worcester Engine Works Company, until ill health obliged him to retire from active work.
In 1872 he went to live at Scarborough, where he resided until the time of his death on 2nd June 1891, at the age of eighty-two.
He was one of the original Members of this Institution on its foundation in 1847; and contributed to the Proceedings other papers on his inventions besides those referred to.
1891 Obituary The Engineer 1891/06/12.