Compressed air hit 'n miss engine

[mklotz]

Hit 'n miss engines are usually internal combustion engines. However, there is no need to deal with all the messiness of IC technology. This is a hit 'n miss that runs on steam, or, for demonstration purposes, compressed air.

When the engine rpm drops low enough, the governor weights drop in and trigger the main air valve. The incoming air pressure activates a spring-loaded ball in the cylinder head to close the normally-open exhaust valve and allow the air pressure to push the piston down. When the air valve closes, the spring reopens the exhaust valve so there won't be back pressure on the piston when it rises.

One of my cameras has a slow motion feature so I shot this video at an exhibition to better visualize the operation of the governor weights.