It moves the electrolyte by means of convection. There are two tubes from the cell to the reservoir. One outlet at the top of the cell and one inlet at the bottom. As the electrolyte heats up it rises to the top of the cell along with the bubbles of HHO. This creates a suction at the bottom of the cell thereby drawing in more electrolyte from the reservoir. You then draw the HHO out of the reservoir via a third tube.
Hope this helps.
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Some days I get the sinking feeling that Orwell was an optimist!