Abstract: A closed hollow pressure container is provided including first and second closed compartments therein. A liquid inlet opens into one of the compartments and a liquid outlet opens outwardly of a lower portion of the second compartment. Gas transfer passage structure is provided communicating the upper portions of the compartments for the transfer of gas under pressure from an upper portion in the first compartment into the upper portion of the second compartment and the container is operatively associated with a liquid pressure flow line including inlet and outlet end portions. The flow line includes flow reducing structure within the line intermediate its inlet and outlet ends and a bleed line communicates the flow line, upstream from the flow reducing structure, with the interior of the first compartment and a restricted flow liquid feed line communicates the lower portion of the second compartment with the flow line downstream from the flow reducing structure.