Pasting a comment from yesterday. The linked video talks about how the double cylinder engine works and shows an up-close of the valves at around the 48 min mark.

If you enjoy videos, Proper People did a fantastic video about a 115 year old steam engine that still works that used to pump water for a city in Massachusetts. Great watch full of info and some beautiful shots. https://youtu.be/nBImv1mlcMg?si=XUyME3AmDB30sKaj