Water falling through a Venturi system sucks in air and compresses the air-bubbles, which are extracted at the lowest point of the system. Water pressure will drive the water up again to the height of the working head.
Referring to the figure at the right, water enters the system from the reservoir through the flume, D. It flows up to C, then pours down to B through small tubes (3/8″ to 112″ diameter), entraining air. The velocity down column E is such that the air remains entrained until it reaches the separating chamber, G. The water returns up column H to be discharged and the air is available via pipe K. The air pressure available is determined by distance G to L and working head of the water is determined by distance M to L. Not shown, a vent pipe may be installed into the separation vessel and extended to the water line. If the air overfills, the water level drops exposing the end of the vent pipe and venting air until the water again rises to submerge the entrance to the vent pipe.