Abstract: An air delivery system introduces a selected amount of aspirated air into a stream of water conducted within a tube. The aspirated air being conducted in an air conducting tube has one end open to the atmosphere, the delivery system includes a flow system in the water tube which has a variable diameter throat and an axis, an outlet system for discharging air into the water stream in a variable spaced relation to the throat, a telescoping system for adjusting the spaced relation of telescopically related water conducting members and a connector between one end of the telescopically related members and the water tube. Movement of the telescopically related water conducting members relative to the throat varies the space between the throat and the air outlet system and accordingly varies the water flow area and the amount of aspirated air.