>>2938691
>what makes a steam pump continuously move?
Exhausting to atmosphere through that black circle that represents the exhaust port on the valve. And the valve on the right side is the pump that pushes the fresh water through the boiler so it can be boiled into steam. To again supply the power stroke on the valve system on the left. Not pictured are the gear reductions and the governor that prevent the system from running at too high of a speed, which would put everything out of the range of timing that provides efficient power delivery.

Gasoline engines have their own valve trains too and they have to control the timing of the intake, compression, and exhaust. They're not any different in operating principle since both take advantage of gas and thermal expansion to produce mechanical force.