dinwitty:
very cool, I noticed the spinning regulator so common on steam traction engines. This regulator helps keep a steady steam to the operatiing machinery despite the variables of steam pressure.
The flyball governor was rebuilt over the winter by one of the FEBT members, the one in the grey t-shirt you see tinkering around the steam chest in the video. It's driven by a 2 inch wide belt that runs to a small pulley next to the big flywheel. The two balls are cast weights that will start to lift by centrifical force as the speed increases. As they lift, they raise a lever that will slowly close the throttle valve, directly below the governor. It will also compensate for varying loads on the engine, since the machines in the shop can be shifted in and out of gear.

A better look at the governor and the machinist who rebuilt it.