Abstract

A pressure displacement dredging system capable of effective and efficient operation, without surging, over a wide depth range and under varying bottom conditions, comprises a submersible dredging head including at least three pressure vessels each having a material intake port and a material discharge port with appropriate check valves, each having an inlet port for air or other operating fluid connected to a high pressure fluid source through an inlet valve and each having an operating fluid exhaust port vented to the atmosphere through an exhaust valve. The system provides cycle control means, actuated by low level sensors in each pressure vessel, which actuates the vessels between discharge and filling phases in a predetermined closed sequence; when the level of material in a first discharging vessel drops below the low level sensor the cycle control opens the inlet valve and closes the exhaust valve for the next vessel in the sequence to initiate pressure displacement discharge of material from that next vessel, and thereafter closes the inlet valve and opens the exhaust valve of the first vessel so that the first vessel fills by pressure displacement, the sequence being such that each pressure vessel is full before discharge of that vessel is initiated. One modification of the system provides a vacuum assist for dredging in extremely shallow conditions.