HYDRAULIC DREDGES 95 



materials from their natural beds, and break the soils in such a 

 manner that they may be readily taken up by the centrifugal 

 pump. 



Suction Pipe. The suction pipe is usually made up of four well- 

 defined parts, which are: the connection to the pump, the joint, the 

 tube proper and the agitator. The connection to the pump is made 

 by an iron or steel pipe running on deck and bent in such a manner 

 as to connect the tube proper with the pump. The joint as a rule 

 is made of rubber; but owing to the wear of such material, it requires 

 continuous repairing. To avoid this inconvenience, connections 

 are now being made on some dredges by means of a ball-and-socket 

 joint. The suction tube proper, which forms the real communication 

 between deck and bottom, is composed of several sections of wrought- 

 iron pipe from 10 to 20 in. in diameter, the size depending upon the 

 efficiency of the dredge. These pipes are made up of sections 20 

 ft. in length each, provided with flanges and riveted together. 

 They can be also made of steel plates welded together. Such pipes 

 are stronger and lighter than those made of wrought iron. It can 

 also be constructed of steel angles and plates. In any case the 

 suction pipe should be strong in order to support either the agitator 

 or rotary cutter attached at its lower end and also the shafts and 

 gears for the rotation of the cutter. The length of this portion 

 of the suction tube varies with the depth and nature of soil 

 encountered. 



Its length, as a rule, is determined in such a way as to have 

 the suction pipe working at an angle of less than 45. At some 

 convenient point the suction tube is provided with a heavy steel 

 ring, to which are fastened wire ropes, which passing over sheaves 

 suspended from a gantry at the end of the boat, are wound around 

 the drums of a reversible engine. In this manner it is possible to 

 raise the suction tube above the level of water when operations 

 are suspended, and lower it again to the bottom to resume 

 work. 



The lower end of the suction tube is usually provided with some 

 devices to feed the tube in the most convenient way. Of the various 

 devices the most commonly used ones are: the scraper, the rotary 

 cutter, and jets of water or compressed air. 



Agitators. The scraperused at the end of the suction tube consists 

 of a wide broadened extension of the pipe so as to dig a furrow as 

 wide as possible. It is covered with a steel apron and is provided 



