Abstract: In combination with a pump, a valve for operation at the interface between underlying heavier liquid and overlying lighter liquid is disclosed. The valve includes an inlet within the heavier liquid communicated from a valve seat to a conduit which typically is connected to the inlet of a pump. A valve disc opens and closes the valve seat to admit the heavier liquid to flow to the pump. The pump is preferably pneumatic and of the type which when flooded with liquid, automatically undertakes pumping and when empty of liquid ceases pumping. A buoyant member having a specific density between that of the lighter liquid and the heavier liquid is buoyantly supported at the interface and moves with the interface. This buoyant member is connected to an assembly which actuates the valve. Where lighter liquid is predominantly present, the float sinks and closes the valve preventing pumping. Where heavier liquid is predominantly present, the float rises, opens the pump inlet to permit pumping.