Here's a larger version, with 'color coded steam' and sound. (Warning: 254K GIF, 0.6 minutes @ 56kbps)
An even larger version with animated cycling of the cutoff and reverse linkage action.
(Warning: 549K GIF, 1.3 minutes @ 56kbps)
...Why?! It's just an experiment to try to satisfy a fascination held with this mechanism (Walschaert valve gear54K GIF) since childhood (late '40s). Whatever...
By the way, Walschaert gear is correct; Walschaerts gear is not (unless it is used in the possessive case, with an apostrophe, eg: "Walschaerts' design"). The inventor's name was (Egide) Walschaerts (pronunciation: ay-gee-da val-sherts), but the design was patented under the name Walschaert for political reasons. Ref: Publications Style Manual,Pennsylvania Railroad Technical and Historical Society.
Some of these illustrations my help answer the question: "How does a steam locomotive work?".
Downloadable freeware simulations of every kind of valve gear you've ever heard of by Charles Dockstader (CA). We're Mac heads here, but we downloaded his .exe files and borrowed a Wintel machine to try them out and were impressed with this work; very cool and enlightening.