Dredge pumps are the beating heart of hydraulic dredgers, giving life to the whole vessel. Without them, slurry transport wouldn’t be possible, and cutter suction dredgers (CSDs) and trailing suction hopper dredgers (TSHDs) wouldn’t exist.
Dredge pumps create a vacuum that sucks the soil from the seabed up into a suction pipe and, in the case of CSDs, pushes it all the way to the discharge site via a pipeline. In TSHDs, dredge pumps transport the soil to the hopper and are also used to discharge it via pipelines or rainbowing.
Dredge pumps are centrifugal pumps, which mainly consist of a pump casing and an impeller. The impeller is mounted into the pump casing and connected to the drive motor through a shaft. The front side of the pump casing is closed using a suction cover, to which the suction tube is connected. The discharge of the dredge pump, mostly situated at the upper side of the pump, is connected to the discharge line.
The impeller can be compared to a fan that displaces air and, by doing so, it creates a centrifugal force. At the inlet/suction pipe, an underpressure or vacuum sucks up the slurry. At the discharge end of the pump, an overpressure transports the slurry up the discharge line.
Dredge pumps in vessels
Small dredgers normally have only one dredge pump, whereas bigger vessels can accommodate multiple pumps. A TSHD, for instance, can be equipped with one or two pumps in a pump room and/or a submergible dredge pump in the suction tube.
When a TSHD is equipped with an underwater pump, the loading of the hopper is usually done with the submerged pump without the help of the pump(s) in the pump room. The ones contained in the pump room are mainly used for discharging the vessel via rainbowing or pumping ashore.
In addition to those on board, CSDs can also be equipped with a submergible dredge pump for extra production and improved suction capabilities. When slurry has to be transported over long distances through a pipeline, booster stations containing additional dredge pumps can also be added to the system.
Selecting a dredge pump
When choosing a dredge pump, the power, efficiency, capacity, resistance to wear, reliability, maintainability and general robustness, are essential features. The required production rate for a certain project in relation to the pipeline configuration, dictates the capacity of the pump, which is expressed in maximum cubic metres per hour.
The soil that needs to be dredged is also a deciding factor when selecting the shape of the dredge pump and the material it is made of. Dredging a mixture of rock and stones, for instance, requires an impact-resistant pump with a larger spherical passage, while sand has highly abrasive qualities where extreme wear-resistant materials are the best option.
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