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Types of dredger

Hydraulic Dredger
The principal characteristic of all dredgers in this category is that the loosened material is raised from its in-situ state in suspension by a pipe system linked to a centrifugal pump. Numerous means might be employed to achieve the initial loosening of the material. If it is naturally very loose, suction alone may be ample, however firmer materials may require mechanical loosening or the use of water jets. Hydraulic dredging is best when working with fine supplies, because they will easily be held in suspension. Coarser supplies – and even gravel – might be worked however with a greater demand on pump power and with larger wear on pumps and pipes.

A Suction Dredger is a stationary dredger used to mine for sand. The suction pipe is pushed vertically right into a sand deposit. If obligatory water jets assist to deliver the sand up. It is loaded into barges or pumped by way of pipeline directly to the reclamation area.

Profile or Plain Suction Dredger
In its most simple type the Profile or Plain Suction Dredger consists of a pontoon able to assist a pump and suction pipe and to make the connection to the offloading pipe. More sophisticated vessels have separate suction and delivery pumps, water jets on the suction inlet and articulated suction pipes. While working, a dredger may be held in position by one or more spuds or, in deeper water, by a posh system of moorings. Plain suction dredgers are primarily used to win fill material for reclamation, with the material being positioned ashore through a floating pipeline. Very long distances will be pumped by the addition of booster pumps within the line. Material may alternatively be loaded directly into barges moored alongside. The normal measures of dimension are the diameter of the offloading pipe, which can range between a hundred and 1,000 mm, or the put in horsepower.
Another use of plain suction dredgers – common within the USA – is to dredge from the navigation channel of a river and side forged the fabric to nearer the bank via a short pipeline or simply by jetting. In this role they are more commonly known as dust-pan dredgers.
Trendy suction dredgers can recover material from great depths and may extract sand from under a clay overburden. Known as a deep suction dredger, this type affords the potential to recover fill materials from depths as much as one hundred m. Production could be very dependent upon the permeability of the fabric dredged and is greatest in clean sands.

A Cutter Suction Dredger is a stationary dredger which makes use of a cutter head to loosen the material to be dredged. It pumps the dredged materials through a pipeline ashore or into barges. While dredging the cutter head describes arcs and is swung around the spud-pole powered by winches. The cutter head could be replaced by several kinds of suction heads for special functions, reminiscent of environmental dredging.
When the in-situ material is too compact to be removed by suction motion alone, some type of mechanical loosening should be incorporated close to the suction mouth. The commonest method is a rotating cutter: the principle function of the cutter suction dredger. This is mounted at the lower finish of the ladder used to assist the cutter drive and the suction pipe. The loosened materials then enters the suction mouth, passes via the suction pipe and pump (or pumps) and into the delivery line.
Cutter suction dredgers operate by swinging a couple of central working spud utilizing moorings leading from the decrease end of the ladder to anchors. By pulling on alternate sides the dredger clears an arc of reduce, and then moves forward by pushing towards the working spud using a spud carriage. A generally smooth bottom may be achieved, and modern instrumentation allows profiles and side slopes to be dredged accurately. Among the bigger cutter suction dredgers are self-propelled to permit straightforward movement from site to site.
The scale of a cutter suction dredger is measured by the diameter of the suction pipe and by the put in machinery power. Pipe diameters are within the range 100 to 1,500 mm. A contemporary highly automated cutter suction dredger is capable of achieving high outputs over sustained intervals and production rates of around 500,000 m³/week are attainable under good conditions.
Cutter suction dredgers can be utilized to deliver by means of a pipe- line or to load barges. They might also be used simply as loosening devices for materials to be re-handled by another type of dredger, in which mode offloading is directly over the strict to the sea. Pipeline offloading is most common however is vulnerable to waves and currents and causes an obstruction to different vessels. To keep away from these problems part of the pipeline may be submerged and laid on the channel-or sea-bed.
Cutter suction dredgers are mainly used for capital dredging, especially when reclamation is related with the dredging. Smaller vessels will be dismantled into sections and moved by road or rail for work in inland waterways, sludge lagoons, reservoirs and similar isolated areas. Massive heavy-duty cutter dredgers are capable of dredging some types of rock which haven’t been pre-treated.
An alternative form of loosening is the usage of a rotating bucket wheel on the suction mouth. Bucket wheel dredgers are most commonly used in mineral extraction operations and to this point haven’t discovered general favour among the major international dredging contractors.

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What is a Dredge Cutter?

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 might be being dredged.

Cutters have primary capabilities:

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 particles into the high-velocity stream on the suction intake in a prescribed capacity where the supplies shall be then pumped and transported by way of a dredge’s hydraulic pipeline system.

Specialised types of dredger are usually of small measurement and output. They include easy 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 particles is minimised. These dredgers are relatively small units and a few may be manoeuvred on spuds alone.
Air-lift dredgers are similar to the jet-lift dredgers however the medium for inducing water and materials flow is high pressure air injected at the mouth of the suction pipe. As with jet-lift dredgers there aren’t any moving parts within the flow system. Hard or other troublesome to loosen materials can’t be dredged.
Augur suction dredgers operate on the identical ideas as a cutter suction dredger, except that the mechanical reducing instrument is a rotating Archimedean screw positioned at proper angles to the suction pipe. The screw dislodges materials, which is fed to the centrally placed suction pipe. Most units have a shroud over the chopping screw which reduces the spread of the plume of disturbed bed materials which normally escapes from all dredgers. The augur suction dredger advances into the cutting face by hauling itself along a wire deployed directly ahead. Very accurate horizontal and vertical dimensions can 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 mostly suspended from a crane on land or from a small pontoon or barge. The dredging action is intermittent and suitable only for simply flowing material.
Amphibious dredgers have the weird function of being able to work afloat or elevated away from the water surface on legs. They are often outfitted with grabs, buckets or a shovel installation.
All of the above specialist types of dredger (and others) have been developed for particular situations and usually for small scale work resembling slender canals, industrial lagoons and reservoirs. Some types have been developed to deal with contaminated sediments with minimum disturbance. They are not normally 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 short 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 materials situated near quay walls and different places the place a trailer can’t attain into a more accessible area. Generally the trailer itself operates the leveller if no tug or work-boat is available.

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