A valve admits steam to one end of a cylinder, pushing back a piston located inside the cylinder.

The valve then admits steam to the other end of the cylinder, pushing the piston in the opposite direction.

The crosshead, connecting rod and crankdisc help to change the back-and-fourth movement into circular motion.

A crankshaft spins, causing the flywheel to revolve.  A belt can transfer the power of the engine to another machine such as a thresher.

An ingenious arrangement involving an eccentric gear changes the rotary motion of the crankshaft back to push-and pull movement, working the valve back and forth.

The governor completes the engine's circle of motion.  It evens out the engine's speed by giving the engine more steam when the engine needs it.