How a Steam Engine Works

This model demonstrates the workings of a typical steam engine, showing the steps of a complete cycle. Compressed air, which is substituted for steam, first flows through a valve into one side of the piston chamber. Next, the air pushes the piston, which drives the shaft. The moving shaft triggers a switch that controls the air valve. Finally, the air flows to the other side of the piston chamber, pushing the piston—and the shaft—in the reverse direction.