Shred
It's running on air. when you run them on air the exhaust is.... well.... air. Run it on water and the mop would have to come out....LOL. I'm tempted to try water through it but I need to tear it down one more time and get some gaskets in place. It's hissing a little bit of air in a couple of spots.
Steve
BTW... there is a second video of the engine on my Youtube account. I was asked to pan around the engine so someone could see a bit more of how it works.