A Quick Look at the Percussion Drill
Percussion drilling gets its name from the action of its drill tools, which rise and fall to beat upon the earth and chop up soil and rock. It is more popularly known today as "Cable Tool Drilling" since the modern drilling rigs use steel cable to lift and drop the tools. The percussion drill has many variations, like the Chinese springboard, the American spring pole, and the walking beam, but they all perform the same functions: lifting and dropping the drill tools to cut the earth and clean out the hole.
The drill tools involve a heavy steel bit which is lowered into a hole on a rope. The bit is lifted, either by hand or by machine, and then dropped to cut the earth. As the bit chops the earth, water is added to the well hole so that the bit makes mud out of the earth it has cut.
After the hole is filled with several feet of mud, the heavy bit is withdrawn and a tool called a bailer is attached to the rope and lowered into the hole. The bailer is a hollow tube with a door at the bottom. The door, called a flap valve, opens when it hits the mud to allow the mud to fill the bailer. Then the flap valve closes to trap the mud inside the tube so that the mud can be lifted to the surface. The bailer is emptied at the surface and returned to the hole, where the procedure is repeated until the hole is clear.
The bit is then re-attached to the rope and the above process begins again.
As long as the earth being drilled does not cave in, the drilling continues until the water table has been penetrated to a proper depth. Then a length of pipe, called casing, is installed in the well hole. The remaining hole around the casing is refilled and sealed. A concrete slab is poured around the new well and a hand pump or bucket is installed.
However, if the earth is made of loose material like sand, a large heavy steel pipe is driven into the hole to keep the walls from falling in. The large pipe is called temporary casing and it holds the hole open until the drilling is done. It is removed after the smaller permanent casing is installed. The temporary steel casing can be reused many times.