Holes are required beneath the earth surface for various applications in geology, hydrology, agriculture, civil engineering, mineral exploration etc. The most common application of down hole drilling is bore well as water source. Water storage under the earth surface is a pure source of water.
Earth crust is consisting of layers with variety of igneous, metamorphic and sedimentary rocks. Drilling the hole through these hard rocky layers is not an easy task. A controlled and powerful drilling mechanism is needed to drill the holes. Rotary air percussion is the one type of method most common and effectively applied for DTH drilling. For DTH drilling there are few more techniques used like auger drilling, Cable tool drilling, Reverse circulation drilling, Direct push drilling etc.
Rotary air percussion is the technique most effectively applied for DTH drilling. Rotary air percussion is a pneumatic method of drilling. A heavy and hard drilling bit fitted below the pneumatic hammer. A reciprocating piston provides the hammering action to the drilling bit. The hammering beat breaks the hard rock surface and converts it into small pieces. The pneumatic source is kept on the earth surface with a rigid pneumatic supply to the hammer, through a string. A series of hollow pipe fitted with each other supply the high pressure compressed air as well as rotary motion to the hammer. This technique is cost effective and very fast.
The heavy flow and high pressure compressed air, discharged from the hammer end lift the crushed rock pieces and water upside, out of the bore. High powered air compressors supplying up to 1200 CFM of air at 350 psi, are used to empower the hammer and lift out the residual with water out of the bore. This method is highly effective and efficient for deep drilling, and can drill down up to 2000 foot. The diameter of the bore is limited up to 8 inches.