Definitions for "Allan Valve Gear"
A form of valve gear patented by Alexander Allan in 1859 when Locomotive Superintendent of the Scottish Central Railway at Perth and also known as 'straight link' motion. Movement is derived from eccentrics on the driving axle. Generally similar to the Stephenson gear but the valve-rod is raised as the link is lowered and the link itself is straight, whereas on the Stephenson gear it is curved. Allan valve gear was used by Webb for many of the passenger engines used on the LNWR.