Abstract: In a lift bag used by divers to lift objects from the ocean bottom to the surface, this invention keeps constant the amount of flotation gas and hence the lift force. A hose connects the gas bubble trapped inside the bag to a point, lower on the bag wall, selected by the diver to give the desired lift force. As the device ascends, lifting the cargo to the surface, any excess volume of gas created by expansion is discharged through the hose. The purpose is to prevent uncontrolled rapid rise of the device which can cause deflation and re-sinking when the lift bag reaches the surface.