SEISMIC METHODS 



879 



Figure 552 shows the mud fluid coming up out of the hole and flowing 

 through the trench to the sump located just to the left of the picture. 



Both the hydraulic feed and the mechanical pull-down type of drill are 

 equipped with multiple-speed transmissions and clutches. The transmissions 

 provide different speeds for the rotation of the drill rods, for the speed of 

 the mud pump, for the rate of the feed, and for the speed of the hoisting 

 drum. The clutches permit the connecting or disconnecting of each of these 

 drives. 



Fig. 551. — Mechanical feed type drill. (A) drive rod or Kelly; 

 (B) rotary table; (C) feed chains; (D) sprockets; (E) combina- 

 tion yoke and swivel; (F) wire rope; (G) guide sheave; (H) wire 

 line; (I) swivel bail. (Courtesy of Mayhew Machine Company.) 



All drills make provision for setting casing where this is necessary. On 

 the hydraulic feed type machine the entire drive-rod assembly is retracted 

 forward from the hole on slide rails far enough to provide ample room for 

 setting or recovering casing. On the mechanical feed drill the opening 

 through the rotary table is usually large enough to set casing through the 

 table. 



