US Patent 4,790,355
United States Patent and Trademark Office
University of Iowa Research Foundation (Iowa City, IA, US)
A vertical dropshaft having internal helicoidal ramps for dissipating the energy of liquid passing through the dropshaft and for exhausting air entrained by the falling liquid up the center of the dropshaft.
Kennedy, John F. Helicoidal ramp dropshaft. US Patent 4,790,355 filed March 23, 1987 and issued December 13, 1988. https://ir.uiowa.edu/patents/61