A cutter refers to the type of excavator head equivalent to a basket cutterhead or bucketwheel on a hydraulic pipeline dredge. The cutter houses the suction intake and is used for slicing or agitating the supplies which are being dredged.
Cutters have two basic capabilities:
Loosen and break up supplies from the underside of a waterway into smaller fragments which can be appropriate with the dredge’s pumping system.
Intro the crumbled debris into the high-velocity stream at the suction intake in a prescribed capacity the place the materials might be then pumped and transported via a dredge’s hydraulic pipeline system.
Specialised types of dredger are often 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 impact of a concentrated high-speed stream of water to draw the adjacent water, collectively with bed material, 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 some can be manoeuvred on spuds alone.
Air-lift dredgers are similar to the jet-lift dredgers however the medium for inducing water and material flow is high pressure air injected at the mouth of the suction pipe. As with jet-lift dredgers there are no moving parts in the flow system. Hard or other troublesome to loosen materials can’t be dredged.
Augur suction dredgers operate on the same principles as a cutter suction dredger, besides that the mechanical cutting software is a rotating Archimedean screw positioned at proper angles to the suction pipe. The screw dislodges material, which is fed to the centrally placed suction pipe. Most units have a shroud over the cutting 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 alongside 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 material is pumped out with the inlets closed. The inlets are then opened and water and materials 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 action is intermittent and suitable only for easily flowing material.
Amphibious dredgers have the bizarre feature 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 specific situations and usually for small scale work equivalent to slender canals, industrial lagoons and reservoirs. Some types have been developed to deal with contaminated sediments with minimal disturbance. They don’t seem to be usually employed for big scale maintenance 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 tactic can be used for direct dredging over quick distances and for levelling off the bed to the desired depth when a trailer or grab dredger is operating. It could even be used to tug away material located close to quay partitions and other places where a trailer can not attain right into a more accessible area. Typically the trailer itself operates the leveller if no tug or work-boat is available.
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