Alexander Allan (locomotive engineer)

Alexander Allan was a Scottish mechanical engineer. He was born at Montrose, Angus, in 1809 and died at Scarborough, Yorkshire on 2 June 1891.

From 1843 to 1853 he was Works Manager at the Crewe Works of the Grand Junction Railway, later London and North Western Railway, under Francis Trevithick. He later claimed the credit for designing the Crewe type locomotive with inclined cylinders and double frames, but this claim has been challenged. From 1853 to 1865 he was Locomotive Superintendent of the Scottish Central Railway. Allan was an original member of the Institution of Mechanical Engineers in 1847.

Allan made a number of inventions, including a balanced slide valve, but the best-known is his straight-link valve gear of 1855.