30,000 pullback rating can be used as an additional hoist. A split centralizer and pipe-handling system located on the ITWD worktable is used to break and make drill pipe  connections,  to  support  the  drill  string  during  pipe handling, to provide a centralizer bushing for the drill string, and to aid in setting casing and making casing joint. The centralizer is a split design consisting of a rear section welded to the main frame and a removable forward section. The forward section is held in place by two pins and can be manually swung out or detached to facilitate setting large diameter casing or surface pipe. The forward section is removed during transport and stored   on   top   of   the   worktable.   The   centralizer accommodates various sizes of split bushings to adapt to a number of drill pipe, casing, and down-hole-drilling hammer   diameters. A hydraulically powered breakout wrench is also mounted on the worktable. This wrench is used with a manual holding wrench (used to support the drill string and stop rotation) to make and break pipe and casing joints. Top-Head Drilling Operations All  personnel  assigned  to  drill  with  the  ITWD should  thoroughly  read  and  understand  the  operator’s manual before proceeding with any drilling operations. Additionally,  SAFETY  IS  PARAMOUNT  over all actions performed during drilling operations. In general, you proceed to set up the rig as follows: Move the rig into position on the selected site. Use the hydraulic outriggers to level the rig and take the weight of  the  rig  off  the  axles.  Ensure  adequate  overhead clearance; then raise and lock the derrick. For the top-head  drilling  rig  proceed  with  the following: 1. Attach the centralizer half to the worktable. 2. Install the centralizer bushings. 3.  Place  the  bottom  holding  wrench  in  position. 4.   Dope   (lubricant   for   threads)   the   top-head spindle  sub  threads. 5. Lower the hoist and attach the hoist plug. 6.  Raise  the  top-head. 7.  Dope  the  tri-cone  bit  threads  (down- hole-drilling hammer treads if hammer drilling). 8. Manually thread the bit into the bit sub. 9. Wrap the mud flinger around the bit sub. 10. Dope the hoist plug threads and thread into the bit sub. 11. Raise the bit sub with the hoist and insert into the  centralizer  bushing. 12. Insert the holding wrench to the support bit sub; close the forward half of the centralizer and pin it shut. 13. Remove the hoist plug from the bit sub. Installation  of  the  Drill  Pipe: 1. Slide the drill pipe sling over the drill pipe. 2. Attach the hoist cable to the drill pipe sling and hoist the drill pipe into position over the bit sub. 3.  Lower  the  top-head  into  position  with  the rotation  on  slow. 4.  Tighten  all  connections  and  raise  the  drill slightly off the holding wrench and remove the holding wrench. Rotary Mud Drilling: 1. The mud pits for top-head drilling are dug and designed, as shown in figure 9-10. 2. Connect the suction hose to the mud standpipe. 3.  Place  the  suction  hose  into  the  mud  pit  and connect the hose to the mud pump inlet. 4.  Set  the  engine  speed  to  the  manufacturer’s recommendations and open the mud pump valve. 5.  Control  the  mud  flow  by  adjusting  the  mud pump  speed. 6. While drilling, adjust the top-head drive spindle rotation and pulldown speed and monitor the mud pump stand pressure to avoid a plugged drill bit or loss of pump  prime. 7. Upon completion of the hole, place the suction hose in a source of clean water and flush the drill pipes and bit. Rotary Air Drilling: 1. Lower the bit to within 4 inches of the ground, and connect the flushing line to the air compressor. 2. Turn on the compressor, open the air valve, and set the engine speed at the speed recommended by the manufacturer. 3. Set the pulldown regulator to a minimum and start  the  top-head  drive  spindle  rotation,  and  set  the pulldown speed to LOW. 9-12