Why Doesn't Thomas Have Piston Cylinders?

Thomas is a steam locomotive with side rods, but it's not clear how steam physically moves his wheels. Why doesn't Thomas have piston cylinders? Or if he does, where are they? This video looks into how Thomas the Tank Engine works on the inside using 2D animation. Background Music: I Don't See the Branches, I See the Leaves by Chris Zabriskie is licensed under a Creative Commons Attribution license (https://creativecommons.org/licenses/...) Source: https://chriszabriskie.bandcamp.com/t... Artist: http://chriszabriskie.com/ Playback speed is edited down to 70%