878 EXPLORATION GEOPHYSICS 



hole" sump, which may be made by positioning a screen or board in a mud 

 ditch, to allow the cuttings to settle out. This procedure will minimize the 

 abrasive materials carried into the pump intake. Figure 550 illustrates the 

 general arrangement. 



The mud fluid is pumped from the pit up through the suction hose and 

 discharged into the swivel hose, and then passes through the water swivel, 

 down through the rod string, and out through the drill bit. This fluid washes 

 the cuttings away from the bit in the bottom of the hole and carries them in 

 suspension to the surface, where the mud flows back to the pit through a 



Fig. 550. — Preferred arrangement for mud pit. A, suction hose, pump 

 intake; B, mud wash coming out of hole; C, baffle board; D, rock cuttings 

 and sludge, to be shoveled out as required. 



small trench (Figure 550). The cuttings settle in the trench or the sump 

 and are shoveled out intermittently as they accumulate. Sometimes a heavy 

 mud fluid or aquagell is circulated to maintain the walls of the drill hole 

 when drilling through caving materials, thus avoiding the necessity of casing 

 the hole. 



Mechanical Feed Type Drills 



In the mechanical feed or chain pull-down rotary drill, the downward 

 pressure or feed on the drill rods or Kelly is accomplished by means of 

 power-driven chains instead of with the hydraulic rams. Figure 551 shows 

 the general arrangement and Figure 552 some of the details of the chain 

 pull-down or mechanically- fed drill. The Kelly (A) is rotated by means 

 of -a small rotary table (B) which corresponds to the drive rod in the 

 hydraulic-type drill. The two long feed chains (C) are driven by sprockets 

 (D) mounted on either side of this rotary table. One end of each pull-down 

 chain is attached to a combination yoke and swivel (E) at the top of the 

 Kelly, and the other end of each chain is attached to a wire rope (F) that 

 passes up over a guide sheave (G) at the top of the mast and back down to 

 the top of the same combination yoke and swivel, so that each length of feed 

 chain with its guide cable forms a complete endless loop. When the clutch 

 driving the feed chain sprockets is released, the combination swivel and 

 yoke can be raised or lowered with the hoist or draw works with the wire 

 line (H) attached to the bail (I) on the swivel, as indicated in Figure 551. 



