A cutter refers to the type of excavator head such as a basket cutterhead or bucketwheel on a hydraulic pipeline dredge. The cutter houses the suction intake and is used for chopping or agitating the supplies which are being dredged.
Cutters have fundamental features:
Loosen and break up materials from the underside of a waterway into smaller fragments that are compatible with the dredge’s pumping system.
Intro the crumbled debris into the high-velocity stream on the suction intake in a prescribed capacity the place the materials shall be then pumped and transported by way of a dredge’s hydraulic pipeline system.
Specialised types of dredger are normally of small size and output. They embody simple jet-lift and air-lift, auger suction, pneumatic and amphibious dredgers.
Jet-lift dredgers use the Venturi effect of a concentrated high-speed stream of water to draw the adjacent water, together with bed materials, right into a delivery pipe. The jet head has no moving parts so blockage by wires and other dock debris is minimised. These dredgers are relatively small units and a few might be manoeuvred on spuds alone.
Air-lift dredgers are very similar to the jet-lift dredgers however the medium for inducing water and material flow is high pressure air injected on the mouth of the suction pipe. As with jet-lift dredgers there aren’t any moving parts in the flow system. Hard or other difficult to loosen materials cannot be dredged.
Augur suction dredgers operate on the identical ideas as a cutter suction dredger, besides that the mechanical slicing tool is a rotating Archimedean screw placed at proper angles to the suction pipe. The screw dislodges materials, which is fed to the centrally positioned suction pipe. Most units have a shroud over the slicing screw which reduces the spread of the plume of disturbed bed material which usually escapes from all dredgers. The augur suction dredger advances into the slicing face by hauling itself along a wire deployed directly ahead. Very accurate horizontal and vertical dimensions will be achieved.
Pneumatic dredgers work on the ‘evacuator’ principle. A chamber with inlets for bed materials is pumped out with the inlets closed. The inlets are then opened and water and material drawn in. The mixture is then pumped out and the cycle repeated. The unit is usually suspended from a crane on land or from a small pontoon or barge. The dredging motion is intermittent and suitable only for easily flowing material.
Amphibious dredgers have the bizarre characteristic of being able to work afloat or elevated away from the water surface on legs. They can be equipped with grabs, buckets or a shovel installation.
All of the above specialist types of dredger (and others) have been developed for particular situations and customarily for small scale work similar to narrow canals, industrial lagoons and reservoirs. Some types have been developed to deal with contaminated sediments with minimal disturbance. They don’t seem to be normally employed for big scale upkeep or capital dredging work.
An additional type of dredger is the plough or bed leveller. This consists of a blade or bar which is pulled behind a suitable tug or work-boat. The method can be utilized for direct dredging over brief distances and for levelling off the bed to the desired depth when a trailer or seize dredger is operating. It could also be used to pull away materials positioned near quay partitions and other places the place a trailer cannot reach into a more accessible area. Typically the trailer itself operates the leveller if no tug or work-boat is available.
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