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primary power plant. The elimination of the obstruction caused by
the chain drive reaching from the drawworks to the rotary table is
also a great convenience.
One of the more significant advances in rotary table design
in recent years has been the inclasion of tower slips (Fig. 10.4) as
an integral part of the table.

Figure 10.4 – Tower slips

The disadvantage of the overhang associated with power
slips that are mounted externally on the table eliminated. The slips
are actuated by air pressure controlled through a pedal at the
driller's position. Through the use of slip bowls the conventional
matter brushing is no longer required. Separate bowls are used for
drill pipe and casing, except for casing 5 1/2 OD or smaller which
can be run through the drill pipe slip bowl. Drill pipe slips can be
changed to casing slips in only a matter of minutes.
The kelly is driven directly from table. The arrangement
avoids the trouble that is sometime experienced by the drilling
crew in getting the kelly bushing to slip into place. The operating
levers forth pinion shaft lock assembly is on top of the pinion shaft
housing, as contrasted with the usual side location. This

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