The original trigger for this high power PVC air cannon used a simple ball valve for the trigger. [Ben] didn’t like this solution – it was hard to open and somewhat unergonomic. The ball valve ...

[Tom Stanton] has designed and made a couple of air-powered 3D printed engines ... while the pin pushes open a ball which acts as the inlet valve to pressurize an intermediate chamber.

WE HUMANS NEED AIR TO LIVE, so we do best around sea level. Airplanes are at their best up high ... an outflow valve, which releases the incoming air at a rate regulated by pressure sensors.