An airlift pump (Fig.8) consists of an open ended pipe or tube into which air is injected; part of the tube being submerged below a free liquid surface. The percentage of the pump submergence varies with the application. Airlift pumps operate because a difference in specific gravity exists between the water outside the tube and the air-water mixture within the tube. The injection of air into the tube lowers the specific gravity of the air and water mixture in the column.