Nearly all the aerators thus described worked under gravity heads and discharged water into the air. In the last two decades of the nineteenth century, Professor Albert R. Leeds and John W. Hyatt patented forced aeration by means of which air or oxygen was discharged into water. In Hyatt's first patent he said by passing the combined water and air through a filter the particles of filtering material would finely subdivide the air and enhance the action. When the air and water were thus combined, the water would absorb the oxygen of the air and the impurities in the water would be consumed or rendered inert. In one of his devices, water was to be passed down through an inverted cone-shaped vessel pierced with holes articulated above with a group of Sprengel air pumps. Water falling through these induction tubes was to suck in air and mingle it with the water. To mix the air and water still more, the combined fluid was to be passed over one or more such devices as small stones, horizontal perforated plates or baffles attached to the inside of the left arm of the U-tube containing the Sprengel pumps. The water was then to be passed up through the right arm of the U-tube, which might also be circumvented into the top of the filter.
In a trade catalog of 1886 Hyatt stated that his aerating system combined 25 percent or more of atmospheric air with water under static pressure, oxidizing the impurities, destroying the conditions favorable to germ propogation, and so regenerating the water that it will keep sweet much longer in pipes and reservoirs than water not so treated.