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BULLETIN 300, U. S. DEPARTMENT OF AGRICULTURE. 



Owing to its long reach, the grab-bucket dredge is often used for 

 levee construction. It, however, is not very extensively used for 

 the excavation of drainage channels, although there are certain con- 

 ditions under which it can be used to greater advantage than can 

 the dipper dredge. It excels in handling the muck found on the 

 prairie lands of southern Louisiana and in certain other localities, 

 and under such conditions is better adapted to ditch and levee con- 

 struction than is the dipper type. The latter, however, is preferable 

 for digging hard soil and stumps. 



THE DRAG-LINE SCRAPER EXCAVATOR. 



The drag-line scraper excavator is a type of dry-land machine that 

 has come into prominence only within the last few years. It has 

 made feasible the cheap construction of much larger ditches and 

 levees than is possible by the use of any other type of machine. 



In the type most commonly used, the engine platform, engine 

 house, and boom are connected and revolve on a turntable which 

 is secured to a lower platform built up of structured steel sections. 

 This is known as the revolving or rotary type and is illustrated in 

 Plate II. Upon the upper surface of the lower platform is riveted 

 the track upon which the swinging circle revolves, and in its center 

 is the pivot bearing. The turntable is a steel-frame circle supported 

 by several wheels which rest upon the track. The upper platform, 

 which is also built up of standard steel sections, is held to the lower 

 platform by means of a central pivot. 



In the stationary type the engine platform is fixed; the boom is 

 pivoted at its lower end and is the only part of the machine which 

 swings. This type is illustrated in Plate IV, figure 2. 



The power equipment of the drag-line excavator may be either 

 steam, gasoline, or electric. Unlike the floating dipper dredge, the 

 internal combustion engine has been used with success on drag-line 

 excavators and meets with favor among contractors. For the steam 

 plant the boiler most commonly used is either the locomotive or the 

 Scotch marine return-flue type. On the smaller machines vertical 

 boilers are sometimes employed. The engines used consist of two 

 sets, the main engines and the swinging engines. The former are 

 set in front and are of the horizontal double-cylinder type, with 

 engines and drums self-contained on a single cast-iron or steel bed 

 plate. 



Sometimes the swinging is done by a mechanism attached to the 

 main engine. Ordinarily, however, separate swinging engines are 

 provided. In the rotary type these engines drive, through a series 

 of gears, a pinion which engages the circular rack on the lower frame. 

 Where electricity can be secured cheaply the machines can be operated 

 very economically by this power. 



