Two cylinders, four pistons

[mklotz]

This is an intriguing, if somewhat impractical, design for a steam engine. There are two cylinders, each open at both ends to the atmosphere. Each cylinder has two pistons. One piston is connected directly to the crosshead fitting via a rod. The other piston is connected to a tube which fits around the rod and connects to the crosshead fitting on the opposite side. Steam or air is admitted to the cylinder between the two pistons and forces them apart - an action that drives both sides of the crank. A similar action occurs in the other cylinder. The oscillating valve on the top of the cylinder block controls the flow of air to the two cylinders.

One advantage, admittedly a very small one, of this design is the fact that neither end of the cylinder needs to be sealed which makes the construction simpler. On the other hand, the price paid for this small simplification is the added complexity of the crossover connections needed to use the force from all four pistons. Regardless, it was a fun engine to build and presented some new challenges that were instructive to solve.