Airlift type dredging apparatus

Claim 1

A dredging apparatus for raising fluid and debris from the ocean floor, including, in combination: (a) a generally vertically oriented elongated hollow body having a lower opening of a first given internal diameter decreasing in an upward direction to terminate in a throat opening of a second given internal diameter to define a venturi entrance, said throat opening immediately increasing in diameter at its exit end to a third given internal diameter to define an upwardly facing horizontal annular step lying in a plane normal to the vertical, said annular step having a plurality of vertical holes passing normally therethrough, the interior wall of said body extending upwardly from said step gradually increasing in internal diameter to an upper opening of a fourth given internal diameter to define a venturi diffuser; (b) conveying means connected to said upper opening; (c) means including a gas line and a plenum chamber surrounding the lower portion of said body defining said venturi entrance for introducing a flow of compressed gas from the exterior of said venturi entrance upwardly through said plurality of vertical holes in said step to said venturi diffuser to draw into said lower opening and venturi entrance, fluid and debris from the ocean floor, said step resulting in cavitation of the flow of said fluid and debris past the exit end of said throat at the step area, to result in a reduced pressure at the step surface to facilitate said flow of gas upwardly through said holes in said step, said fluid and debris passing up said conveying means and (d) at least one pipe section connected to one of said openings and extending downwardly into said plenum chamber to terminate short of the bottom of said chamber, for enabling removal of any liquid trapped in said plenum chamber.