There are several items, including three simulators, of particular interest to the valve gear student, all downloadable without charge. To download or link as appropriate, simply click the blue highlight.
The 1943 Paper reprint detailing the history of valve gears entitled THEEVOLUTION of VALVE GEARS is available at www.teepublishing.co.uk
Don Ashton's book specifically written for those wishing to design Walschaerts’ and Stephenson’s gears. Basic calculations, geometric propositions and essential reading for an understanding of the mechanisms. Privately published and available as above.
Prof. Bill Hall always took great pains to verify theories by precise experiment and produced a particularly useful program to calculate the benefits of superheating and enabling IHPs at various speeds and pressures to be evaluated. PERFORM is available here.
H.S.Gowan, a most methodical and knowledgeable Canadian National Railways engineer, wrote a definite design document on Stephenson's valve gear for the SMEE Journal in 1975. With due acknowledgment this is downloadable here as a Word document with accompanying diagrams. The diagrams may be enlarged within Word.