Typically water rushing down the vertical pipe falls through a venturi where an external port allows air to be sucked in with it, as the air goes down the pipe it is pressurized proportional to the hydraulic head.
Typically water rushing down the vertical pipe falls through a venturi. The air goes down the pipe. It is pressurized proportional to the hydraulic head the pipe. An external port allows air. This was to be sucked in with it.