colin hayes's List: gravel suction equip/ dredges

• Although this method has largely been replaced by modern methods, some dredging is done by small-scale miners using suction dredges. These are small machines that float on the water and are usually operated by one or two people. A suction dredge consists of a sluice box supported by pontoons, attached to a suction hose which is controlled by the miner working beneath the water.

   

  State dredging permits in many of the United States gold-dredging areas specify a seasonal time period and area closures to avoid conflicts between dredgers and the spawning time of fish populations. Some states, such as Montana, require an extensive permitting procedure, including permits from the U. S. Corps of Engineers, the Montana Department of Environmental Quality, and the local county water-quality boards.

   

  Some large suction dredges (100 hp+ 10 inch) are used in commercial production throughout the world. Small suction dredges are much more efficient at extracting smaller gold than the old "bucket line" was. This has improved the chances of finding gold. Smaller dredges with 2 to 4-inch (100 mm) suction tubes are used to sample areas behind boulders and along potential pay streaks, until "color" (gold) appears.

   

  Other larger scale dredging operations take place on exposed river gravel bars at seasonal low water. These operations typically use a land-based excavator to feed a gravel-screening plant and sluicebox floating in a temporary pond. The pond is excavated in the gravel bar and filled from the natural water table. "Pay" gravel is excavated from the front face of the pond and processed through the floating plant, with the gold trapped in the onboard sluicebox and tailings stacked behind the plant, steadily filling in the back of the pond as the operation moves forward. This type of gold mining is characterized by its low cost, as each rock is moved only once. It also has low environmental impact, as no stripping of vegetation or overburden is necessary, and all process water is fully recycled. Such operations are typical on New Zealand's South Island and in the Klondike region of Canada.

• A suction excavator or vacuum excavator is a construction vehicle that removes earth from a hole on land, or removes heavy debris on land, from various places, by powerful suction through a wide suction pipe which is up to a foot or so diameter. The suction inlet air speed may be up to 100 meters/second = over 200 mph.

   

  The suction nozzle may have two handles for a man to hold it b

• Suction excavators are is useful in being able to remove earth from around existing buried services or tree roots with much less risk of damaging them than using a conventional excavator with a metal scoop.

   

  This type of excavation is held to be a safe and efficient form of excavation. However it is totally unsuitable for archaeological excavation. Using a powerful vacuum and high pressure water, precise holes, trenches and tunnels can be cut to the required size and proportion. Because compressed air or water is used to loosen the earth, the risk of damaging underground utilities is less and contractors can safely find and expose them. Often excavation reveals unknown utilities, saving lives, money and time.

   

  It is also referred to as "daylighting" as the underground utilities are exposed to daylight during the process.

   

  This type of excavating is quickly becoming recognized as a best practice^[3] when working in areas with underground utility congestion and frozen ground. Hydro excavation lessens the risk of damaging utilities, which may often be inaccurately mapped and located and marked on the surface.

   

  A suction excavator is useful in bulk excavation in confined areas, where its suction hose can reach in over or through barriers, e.g. digging a swimming pool in a courtyard.

   

  It can be used on railways (perhaps mounted on a railroad car base) to suck old track ballast off the track when re-ballasting the track.

   

  It can be used as a very heavy-duty vacuum cleaner to pick up miscellaneous debris, e,g, rubble, or big accumulations of fallen leaves or litter.

   

  It can suck up liquids, e.g. water from a hollow.

• international freight forwarder
• An international freight forwarder is an agent for the exporter in moving cargo to an  overseas destination.
• Exporters should seriously consider having the freight forwarder handle the formidable  amount of documentation that exporting requires as forwarders are specialists in this  process.

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