Steam Engine - Part 3

At the engine, the steam goes first into a slide valve, which is like a flexible hose that feeds the steam first into one end of the cylinder, and then into the other. Within the cylinder, the steam pushes a piston back and forth. A rod attached to the piston and extending out through one end of the cylinder, transfers the back and forth motion of the piston to a crank that changes the back and forth motion into a rotary motion.

The crank, in turn, is attached to a device called an eccentric that changes the rotary motion of the crank into a back and forth motion. A rod attached to the eccentric transfers its motion to the slide valve, to drive it back and forth so that it feeds steam first into one end of the cylinder and then the other.

The crank is also attached to a large wheel called a flywheel. It is about five feet in diameter, over a foot wide and made out of cast iron; it weighs about 1,800 pounds. One of Newton’s laws of motion is that a body in motion tends to stay in motion, and that is what the flywheel contributes to the operation of the steam engine. The flywheel helps the piston change direction at the end of each stroke when the steam has stopped pushing in one direction and before the steam has begun pushing the piston in the other direction, and the flywheel smooths out any jerkiness of the piston’s motion.

A wide leather belt connects the flywheel with some pulleys and another leather belt to transfer the motion of the flywheel to the line shaft that formerly carried the motion generated by the steam engine 70 feet up the hill to the pack house.

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Pictures of the steam engine at Hagley are posted on Facebook:

https://www.facebook.com/gil.hahn.3/media_set?set=a.627985140634731.1073741830.100002697535785&type=3