10/28/2022 0 Comments Hand dredge![]() ![]() A pump is fully primed when water is observed flowing out of the discharge end of the pump. This will cause water to become pumped into the foot valve assembly into the pump. Priming the pump on some of the smaller models is accomplished by thrusting the foot valve back and forth under the surface of the water in a reciprocating motion. Without the presence of water in the pump, friction could cause a seal to overheat and require replacement. All jetting pumps provided with our dredges have a mechanical water pump seal. #HAND DREDGE FULL#This means the pump must be full of water and all air removed. "Before starting the engine, the pump must be fully primed. Simple fire fighting type high pressure, high volume pumps are employed which need to be primed before starting the motor. Nearly all dredge pumps are not self priming because the mechanism that enable self priming results in a less efficient pump. The foot valve is a one way valve with a screen. The diagram below shows a basic suction dredge flowchart. Larger dredges may employ gold wheels or other devices to aid in the cleanup of the concentrates. The riffles and carpet are removed and all material (concentrates) in the box washed into a tub and panned out with a simple gold pan. The sluice box normally need not be cleaned out more than once a day at the end of the day. The operator can therefore stay at the nozzle and process material until the motor runs out of gas and needs refilling. A properly set up sluice box does not need tending - all the material sucked up passes over the riffles with no extra attention needed by the operator. In normal operation a gold dredge is run by an operator at the intake nozzle who directs the nozzle and who captures and discards oversized rocks that would plug the intake hose. Second, a 2" pump can easily be used with a venturi to create suction in a 4" hose, greatly increasing the volume of material that can be processed.Ī common suction gold dredge design - 4" surface dredge with air compressor First, gravel pumps are very expensive, heavy, and high maintenance items. The pump actually pumps only water, which is delivered to a venturi type device (called a power jet or a suction nozzle) which indirectly creates suction in a larger hose. A common misperception is that gravel is sucked through the pump. Nozzles sizes may be up to 2" smaller than hose sizes.Ī gold dredge is powered by a motor and pump. What a dredge manufacturer calls a 5" dredge may be a 4" intake nozzle dredge for permitting purposes. This is a very important thing to remember when working with permits. Therefore most dredge permits refer to the nozzle size, not the hose size, when imposing rules and restrictions. The volume of material processed is determined by the nozzle opening, not the inside diameter of the hose. A 5" dredge may have a nozzle opening of 4" for this reason. ![]() However, nozzles are used on dredges which restrict the intake to a size smaller than the inside diameter to help prevent clogs. So a 5" dredge has a main suction hose with a 5" inside diameter. Manufacturers rate suction dredges by the inside diameter of the main suction hose. Floats are also needed because there is rarely a nice gravel bar in just the right place to set up a dredge without floats. ![]() Every inch of vertical lift above the surface of the water robs power/suction from the system. This is because a dredge has just enough power to lift water and gravel to just above the surface of the water. Dredges almost always need to be mounted on a set of floats. A sluice box works because gold is 15 times heavier than sand and gravel and so is easily trapped by the riffles and carpet in the sluice box. Material is transported from underwater to the surface and run through a sluice box to capture the gold. A suction gold dredge is basically an underwater vacuum cleaner. ![]()
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