182 



A TREATISE ON DREDGES AND DREDGING 



independent of the hoisting chains and of the position of the 

 bucket. 



The construction of the bucket is seen from the sectional draw- 

 ing, Fig. 57. The central part of the bucket is the frame A, which 



terminates at the top in a fork B, and 

 at the bottom in a cylinder C; be- 

 tween the arms of the fork is pivoted 

 a compensating bar D, to the ends 

 of which are attached the hoisting 

 chains, and at the bottom of the 

 cylinder there is a wedge-shaped 

 cylinder-head guard E. The com- 

 pensating bar serves to keep the 

 bucket vertical in descending, while 

 the cylinder-head guard serves as a 

 means for anchoring the bucket or 

 for holding it while filling in a fixed 

 position in the material to be re- 

 moved. The shells F F of the 

 bucket are hinged to the frame by 

 four bucket arms G, and are also 

 hinged to the crosshead T by the 

 triangular connecting links H. This 

 crosshead is keyed to the top of the 

 piston rod and slides between interior 

 guides on the two members of the 

 frame. 



In operation, the jaws or shells 

 of the bucket are both opened and 

 closed by the positive action of the 



air pressure upon the bottom or top of the piston. The air is con- 

 veyed to the cylinder from the receiver on the dredge through a 

 double-barreled or Siamese hose arranged as described later. It 

 will be observed from the drawing that the opening and closing 

 mechanism is wholly independent of the devices by which the 

 bucket is hoisted and lowered, so that it may be closed at any 

 point in its vertical travel. Furthermore, it will be seen that when 

 the bucket rests on the bottom its whole weight is effective for 

 digging, the hoisting chains remaining slack until the jaws are 

 closed. 



FIG. 57. Sectional View of the 

 Clamshell Bucket "Arnold." 



