This is an animation of a shaft governor. The idea is to connect yellow cam arm to valve rod which is connected a sliding valve. This regulates the steam going to the steam locomotive piston. Initially when the weight are in the closed position, regulator sends more steam to the piston with a process called late cutoff. That is why we here slow “chuuuf” “chuuuf” sound when the train start moving. When the train gain speed regulator send less steam a process called early cutoff. In this case we here rapid “chuf chuf ” sound. Since I can’t find good drawing showing whole system, early cutoff is not working as I planned, however late cutoff seams OK.