Abstract: A submersible pump casing is supported for limited vertical movement. Buoyancy of the casing changes according to the amount of water in the chamber. When pressurized air continuously supplied to the chamber has discharged most of the water, the casing rises, opening a vent and allowing an inrush of water through a large inlet at the bottom of the casing. A float closes the vent and the cycle repeats. The vent is a simple flapper, and the vent itself is large whereby the filling is quickly accomplished. The flapper is cracked to allow quick opening by a simple push rod and bar mechanism.