Conversion of operating characteristics of suction dredges from water to slurry

Abstract

Published recommendations [1][2][3][8][9][10][11][12] for conversion of head, power, and efficiency characteristics of suction dredges from water to slurry are quite contradictory. Using different recommendations for converting the head of a dredge can lead to an error ranging from 10 to 15%, depending on the dredge type and the specific gravity of the slurry.To improve the formulas the authors conducted in 1966-1970 special investigations in the mechanization laboratory of the Ukranian Hydrologic and Reclamation Scientific-Research Institute (Ukr.NIIGiM) and on many operating dredges and analyzed the experimental results of other investigators from whom the necessary basic data are available. Tests were conducted with 2.5 NF, 10 Gru-8Z, 3 GM-2M, and 16 Gru-8/ dredges working in gravel-sand mixtures and in gravel, sandy, sandy-loam, and loamy soils. During the tests alloperatingparametersofthedredges were recorded automatically, which insured highly accurate measurements. Accuracy of the recorded parameters was attained by the use of highly sensitive sensors and of an ~PP-09M2 instrument which'records vacuum, pressure, readings of the discharge meter, and head loss at the intake. The transportability coefficient was used as the principal characteristic of the material in striving for a combined method of computing the hydrotransport in which this characteristic is used [5] and of computing the operating characteristics for dredges working with a slurry.The transportability coefficient is a variant of impact resistance and depends on the diameter and hydraulic particle size: +, = C$.0.z S /, ~" \ 1.5where C~ = gd/W 2 is the impact resistance coefficient; d is the particle diameter; and W is the hydraulic size.Numerical values of ~. were determined by the formulawhere ~b i is the transportability coefficient for the given size range taken from [5]; and Pi is the content of the given fraction, in %.In previously conducted studies we used the VNIINerud data for the 10 Gru-8t and 5 GR-8 suction dredges pumping sand, a sand-gravel mixture, and gravel, MISI data for a 3 GM-2 dredge pumping sands (day = 0.32 and 1.9 mm) and gravel (dav = 7.36 mm); experiments of the Hydromechanics Institute, AS Ukr. SSR, with a 1000-80 dredge working in sand; and VNIIGidromash data for a 1000-80 dredge pumping fine sand (day = 0.50 to 1.0 mm). The test data were selected with the following conditions: a) the dredge operated in a regime which excluded distort_ton of the head characteristic by cavitation; b) detailed data on the characteristics of the pumped material were available; c) the method of measuring the principal parameters of dredge operation gave sufficient accuracy.