What is the suction lift dredge11/13/2023 It is, therefore, evident that, even in favourable circumstances, the suction dredge in gold dredging requires considerably more power than the bucket dredge, the excess being largely due to the large quantity of superfluous water lifted with the gravel. (3.) That the suction dredge, working in exceptionally favourable circumstances-namely, where 95 per cent, of the material to be lifted was fine gravel-consumed 94.4 horsepower on the 47,745 foot-pounds of work required to raise 35 tons of solid material through 35 ft., together with the necessary water through 15 ft., while the Sew Hoy bucket dredge needed only 67.7 horsepower for the 54,130 foot-pounds of work necessary to raise 50 tons of solid material through 29 ft., and the necessary water through 15 ft., and the Kanieri dredge took only 107 horse-power to accomplish the 83,400 foot-pounds of work, representing the raising of 75 tons of solid material through 30 ft., and of the necessary water through 15 ft. (2.) That in bucket dredges, the actual engine power is roughly seven times that theoretically sufficient to do the work. These results cannot be called conclusive, but they serve to show: (1.) That the frictional losses of power in gold-dredging are very great, probably 600 to 700 per cent, of the power theoretically sufficient to do the lifting work. The difference in the weight of the gravel lifted, while under the water level, has been disregarded and, in estimating the steam power in compound engines, it is assumed that the low-pressure develops the same power as the high-pressure cylinder. The calculations are made in theoretical horsepower, and for easy references are given in tabular form. In calculating the horse-power consumed by suction and by bucket dredges, figures have been taken from the various official reports on the mining industry in New Zealand, dates and pages in each instance being given.
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