Hi Lang et al.
My bet is that the bit you are referring to as an exhaust is actually the intake with a filter vice a spark arrestor on the end. You need it flexible so you can station it upwind of the exhaust and up above road dust etc.
This would point to the air compressor being for breathing air as an actuator cylinder wouldn't care if the air was contaminated with a bit of hydrocarbon contaminated gas... human lungs get most upset at hydrocarbons under pressure and develop lipoid pneumonia... treatable but not curable.
Perhaps the big cylinders are for oxygen and the operator(s) would mix the breathing air into the smaller aircraft cylinders much the way we mix nitrox today; so I'm with Lang, sort of... a breathing air compressor with onboard oxygen to do the mixing.
Cheers! Mike
(Professional Association of Diving Instructors 202,398)
