Patent ID: 8535018

Claim:
A system for pumping liquid comprising: two liquid columns for reaching a body of liquid at their bottom, each liquid column comprising a liquid level detector and a unidirectional valve allowing liquid to flow upward; an upper conduit for sealably connecting to tops of the two liquid columns so as to form a continuous conduit between the unidirectional valves of the two liquid columns; a sealable gas valve for extracting gas from the upper conduit; an actuated conduit having ends connecting to each of the two liquid columns above their unidirectional valve, the actuated conduit comprising, at each end, a unidirectional valve allowing liquid to flow inward from each of the two columns, wherein the unidirectional valves of the actuated conduit are located on a different axis than the axis on which the unidirectional valves of the two liquid columns are arranged the actuated conduit further comprising, between its two unidirectional valves, a switched valve allowing liquid to flow out of the system from one end of the liquid columns at a time; and a controller connected to the liquid level detectors and to the sealable gas valve, for controlling the switched valve and the sealable gas valve so that opening of the gas valve allows extraction of a gas from the upper conduit via the sealable gas valve to cause a rise of liquid in each of the two liquid columns to a starting level, sealing of the gas valve causes liquid from one of the liquid columns to flow out of the system through the actuated conduit and through the switched valve; and the controller further configured to switch the switched valve to allow liquid to flow from another one of the liquid columns as the liquid level in the one of the liquid columns reaches a minimum level.