<p>A device for generating a plurality of gas bubbles in a liquid. The device includes a conduit adapted to carry the liquid. A first gas chamber is formed near the conduit and an orifice proximate a side wall of the conduit defines a passageway between the first gas chamber and the conduit. A valve member is adapted to seat against and close the orifice. The device may include a second gas chamber and a diaphragm responsive to gas pressure in the second gas chamber. A conduit connecting the first and second chambers may include a variable vent for controlling the size and number of gas bubbles injected into the liquid flowing in the conduit.</p>