Joy's Valve Simulation, by Simon Fraser, enhanced by Peter Lawrence

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Feb 22, 2020
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this is a simulation of Joy's Valve Gear, originally written by Simon Fraser, and slightly modified and enhanced by myself. its written in javascript, so runs in any browser window, and is easily modified. it currently simulates the original Muncaster Joy's Valve Engine, as well has a couple I added, the Van Vleck and the Davy Bros triple expansions, and the LNWR loco "Wessie" (pretty much every Joy's Valve Gear I could find on the internet)

download the tar-gzip file into a new clean directory and untar it with "tar -x -z <"
this will create the directory "latest" and all its subdirectories and files,
point your browser at "file://......./latest/index.html" and there you go.

Here's my take on designing Joy's Valve Gear, if you want symmetrical forward and reverse action then you want the "ellipse" being drawn in the lower right of the simulation to be nearly the same ellipse in both forward and reverse, or at least the points where the ellipse crosses the "valve events" and it seems this can be accomplished with
the radius rod and lower rod should be equal length,
and the trunnion pivot and lower link should be equally offset from the cylinder center
though Muncaster deviates a bit from this, so its not all that critical
the radius link should travel equally from vertical going from TDC to BDC, ditto for lower link
in my Muncaster the radius link goes approx +/- 25-deg, and lower link approx +/- 45-deg
I will add a drawing to show what I mean when I figure out a convenient way to do that (without CAD)


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