Assisting Pumps for Dredging
Widely varying particle sizes commonly encountered in dredging situations have a broad range of settling velocities. To reduce suction side losses of an on-board centrifugal dredge pump, normally the suction side velocities are kept comparatively lower. This velocity may sometimes reach the threshold of settling velocity, inducing heterogeneous flow within the pipe that would cause increased abrasion within the inner surface of the suction tube and triggers blockage in the suction side of the centrifugal dredge pump. Two types of pumping devices were developed and used in actual dredging. The results were found satisfactory. To reduce abrasion an energy input in the form of high-velocity water jets to the boundary layer was done. The jets are placed spirally along the inner surface of the pump tube. This spiral pumping device placed before the centrifugal dredge pump also gives a pre-rotation of the mixture assisting the dredge pump thus increasing overall pumping efficiency of the pumping system. Another method to avoid blockage in the suction side and consequently within the delivery pipeline is to place a peripheral-type educator pump in series with the centrifugal dredge pump between the suction mouth of the dredging system and the centrifugal dredge pump. The driving powers of both the systems are high-pressure water. This paper describes briefly these two assisting pumping systems.