98 



A TREATISE ON DREDGES AND DREDGING 



suction pipe 

 cess. 



>ipe, after being loosened by the jets, but without suc- 



For working in sand, water jets for breaking down the mate rial 

 to be dredged are preferred to rotary cutters by engineers on 

 the Mississippi River. At first water jets 9 or 10 in number 2! 

 to 3 in. in diameter with a pressure of 14 Ibs. per sq.in. wero 

 used, but subsequently much better results were obtained by jets 

 1J in. in diameter, 6 in number, with a pressure of Go Ibs. per 

 .in. 

 Instead of jets of water compressed air could be used for dislodging 



sq.in. 



FIGS. 27 and 28. Cross-section and Side View of the Centrifugal Pump of a 



Hydraulic Dredge. 



the material from the bottom, but the same objections exist against 

 air jets. 



Pump. The most essential part of the hydraulic dredge is the 

 centrifugal pump. When the dredge is designed to work only 

 through finely divided soils any pump of ordinary construction 

 will be found satisfactory; but when the dredge operates through 

 hard and compact soils special attention should be given to designing 

 the shell of the pump, which should be strong enough to resist the 

 violent blows caused by stones thrown against the inner surface of 

 the shell by the impact of the flowing water and materials carried in 

 suspension. The shell is usually made of cast steel or cast iron 



