Steam engine valve gear simulation


Perhaps the most fascinating aspect of steam engines is the beautiful motion of the exposed rods and linkages.  The mechanism that is commonly highly visible on locomotives has the important task of operating the steam valves that distribute steam to the cylinders.  It’s an interesting study in kinematics, but one needs to achieve precise dimensions and mechanical relationships if the engine is to work well.  Engineers and observers have argued long and hard about the design of the “best” valve gear for an engine.  When I started building “Speedy” I was given several alternative designs, and I wanted to understand what the differences really were and why the respective designers made their choices.  At the time, I was writing programs to solve the kinematics for a sheep shearing robot, so I sat down and simulated the valve gears on my computer.




I added other generic valve gear designs and the programs are FREEWARE, and have been used around the world for full sized as well as model engines.  If you are building or restoring an engine, it’s worth checking the valve gear design for the quality of the valve events before cutting metal.


After you download these zip files, unzip them into their own directory.


Download the Windows version (277KB)

(The Windows version simulates these forms of valvegear: Walschaerts, Stephensons, Bakers)

The program is being used for the exciting new 5AT Project



Download the DOS version (649KB)

(The DOS version simulates these forms of valvegear: Walschaerts, Stephensons, Bakers, Allen, Marshall, Hackworth, Joy, Baguley, Simple Eccentric)


Valve Gear Design with Don Ashton


Don is a recognised expert in valve gear design and is author of “Design Procedures for Walschaerts’ and Stephenson’s Valve Gears” (Camden Miniature Steam Services ).


I can do no better than to link you to Don’s own website:


He has kindly provided design spreadsheets for the most popular gears.  These provide inputs that can be easily inserted into the simulation programs.


Don has published articles on simulators in the Australian Model Engineer, Issue 127, July 2006, page 31, and issue 131, March 2007, page 39. Here’s an article on simulators: SIMULATORS.pdf