TM 5-3820-256-10
(b)
Position a piece of timber, larger than the hole, under the hammer. Lower the hammer onto the
timber.
(c)
Apply enough pulldown pressure to keep the bit pushed against the hammer. The hammer piston
should begin striking the bit at high frequency; the air gage should read 100 to 110 psi.
(d)
Turn off the air and remove the timber.
(6)
When starting a new hole, begin drilling as follows:
(a)
Lower the bit to just above the ground.
(b)
Turn on the air for 100 to 110 psi.
(c)
Start slow rotation at about 5 rpm.
(d)
Lower the bit to the surface.
(e)
Apply pulldown pressure to start penetration. Proceed carefully to keep the bit from "walking" on the
surface.
(f)
Start the water injection to control dust.
(g)
After the hole is 18 to 24 inches deep, increase rotation to approximately 25 rpm. Maintain enough
pulldown pressure to effect an adequate drilling rate.
(7)
When continuing a hole, you may not be able to add all the joints of pipe that were removed, depending on
whether or not the kelly was drilled down completely, and considering the added length of the hammer.
Before adding the last joint of pipe removed, attach the kelly. Then proceed as follows:
(a)
Lower the bit to the bottom of the hole.
(b)
Turn on the air for 100 to 110 psi.
(c)
Start rotation at about 25 rpm.
(d)
Apply pulldown pressure to start penetration.
(e)
Start the water injection to control dust.
(8)
Continue drilling. Start the force feed lubricator to inject lubricant for the DTH hammer.
f. Coming out of the hole.
(1)
When the hole is drilled to the required depth, when the bit is worn out, or when drilling conditions warrant
the use of the down-the-hole hammer, all the pipe must be withdrawn from the hole. This is accomplished
by removing
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