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)
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 www.camdenmin.co.uk ).
I can do no
better than to link you to Don’s own website: http://www.donashton.co.uk/
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. www.ameng.com.au. Here’s an article on
simulators: SIMULATORS.pdf