I was inspired to build an air engine, that is, one that is driven by an air pressure difference, by Matthias Wandel. For those of you not familiar with his work I heartily encourage you to look into his YouTube channel or his website woodgears.ca. His projects are great and the quality of his videos is very high. Matthias sells plans for an air engine, although I did not use them but made up my own design.
Here is a quick video of it in operation.
The engine will run from either a source of vacuum or pressure. The video shows it running on my shop vacuum. Except for the screws in the bearing caps of the crankshaft it is made completely of wood. It is a "dual-action" design. That is, the piston is alternately driven from above, then below, as opposed to an internal combustion engine, for instance, where the piston is only driven from above.
The cylinder has two ports, one near each end. Then there is a valve mechanism that switches the vacuum or pressure between the two ports, coordinated with the movement of the piston.
One more thing. I would encourage the interested reader to look on the Jay Leno's Garage YouTube channel for the "1832 Steam Engine" video. This is a stationary steam engine that was used to power a factory that Jay has restored to working order. If you've never seen one of these large steam engines running you will be surprised at how quiet and, dare I say, beautiful they are in operation.