Between 1100 BC and today, there have been many variations of the percussion tool, but the basic design has remained the same. For most types of soil, the percussion drill is a solid, reliable, and fast way to make a low cost well. As a simple technology for developing countries, the percussion drill has a lot going for it. The drill design is adaptable to whatever level of technology is available. It can be made from scrap steel and carried into remote, road less areas. It can be powered by a dozen men pulling on a rope, or by a system of levers and springs, or by an automobile, or by any size engine mounted on a truck bed. A driller trained on one system can easily adapt to any one of the others, thus allowing simple drilling programs future expansion possibilities.
Percussion drilling is easily learned and can be practiced
without much formal training. In the case of the simpler
hand-powered systems, a full drill can be constructed from $200
to $300 in easily designed tools and free or low-cost local
materials (like poles, sticks, twine, etc.). So it is possible to
train local craftsmen to be drillers and for them to equip
themselves inexpensively. Also, since the tools can be used to
drill numerous wells before needing replacement, the driller can
work locally at a wage rate that can be afforded by his
community, supplying the much needed economic incentive that can
both attract and hold craftsmen to the business of water
The Wellspring Africa Handbook
This handbook is the result of several years of research by
many, the advice of professional drillers, and a well drilling
project carried out by Wellspring Africa in the southeast of
Liberia, West Africa. Most of the pictures in this manual are
from the Liberian project. Through most of this manual I describe
the basic hand powered drilling method, though I discuss other
drilling methods in the final chapter.
How the Percussion Drill Works
Percussion drilling gets its name from the action of its drill which raises and falls to beat upon the earth and chop up the soil and rock. It is more popularly known today as "Cable Tool Drilling" since the more modern drilling rigs use steel cable. It has many variations, like the Chinese springboard, the American springpole, and the walking beam, but all employ the same basic means of cutting the earth and clearing out the hole.
The drill involves a heavy steel bit attached to a rope which 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, and then closes to trap the mud inside the tube so that the mud can be lifted to the surface. The tube is emptied at the surface and the procedure is repeated until the hole is clear.
The bit is then re-attached to the rope and the above process begins again.
If the earth being drilled will not cave in, then the drilling continues until water is reached. But 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 casing and it holds the hole open until the drilling is done. It is removed after the permanent casing (usually smaller) is installed. The larger steel casing can be used many times.
When the water level has been reached the drilling stops and
the permanent casing, which is smaller than the well hole, is
installed. Then the rest of the hole around the casing is filled
and sealed. A concrete slab is laid about the new well and a hand
pump is installed.
The Advantages of the Hand Powered Percussion Drill
Percussion drills have been used to drill thousands of feet, though they are generally used for wells from 30 to 250 feet deep.
The bore holes made by percussion drills are markedly easier to protect from contamination than their counterpart, the hand dug well. This is because the small size of the hole and the ease of sealing the well casing so that surface water cannot flow back into the well along the bore hole. Compared to digging wells by hand, the percussion drill can represent great savings in well production costs.
At first consideration, it may seem that any method which involves special tools, ropes, and pulleys could not be less expensive than a method that only requires an axe and a shovel. But when digging and drilling costs are compared side-by-side, the percussion drill proves remarkably cheaper.
Because clearing a larger hand-dug hole requires more labor, and protecting such a large hole requires more materials, the hand dug well proves more expensive overall.
One factor that is both an advantage and a limitation of the percussion drill is that it makes a narrow hole, from six to twelve inches wide. This usually requires a hand pump to remove the water from the well. Using an inexpensive and simple pump like the Consallen hand pump, which is an excellent example of the United Nation's VLOM (Village-Level Operation and Maintenance) ideal, nearly assures that the well will remain free from the spoilage problems that have plagued hand dug wells. (Drilled wells with 6 inch or larger steel casing may be used as a bucket well, however.)
In the final comparison, the percussion drill has many features that simply out-perform the hand digging method: percussion drills can drill hundreds of feet (one hand drilled well, completed in 1923 in China, was 4000 feet deep); percussion drills can drill further into the water table than dug wells, even drilling past one water table to reach another; and percussion drills can drill effectively and quickly through most types of earth.
Percussion drills have not been favored by developing entities promoting appropriate technology mostly because of the percussion drill's huge cousin: the Cable Tool drill. The modern day Cable Tool drill uses the same technique as the percussion drill, but in much larger sizes. The Cable Tool drill uses steel cable to lift and drop steel bits which may weigh as much as a ton. The smaller bits and bailers for the Cable Tool drill are ten feet long and its diesel-powered mechanisms are very costly to build and maintain. Many in the developing field have recognized that the larger machines like the Cable Tool drill are not often an appropriate technology for those who need to construct wells.
But the hand powered percussion drill, which was used to make the first wells in Asia, Europe, and the United States, is a time-tested tool that is easy to build and inexpensive to maintain. The cost of the drill is minimal and its flexibility is outstanding. (It can even be used to drill blast holes for dynamite in landscaping, quarrying, and road-building.)
The percussion drill can be powered by hand, with several men pulling on a rope to lift and drop the bit, or it can harness the power of an engine. It can take the form of a few pieces that can be transported in the trunk of a car and carried into remote villages, or it can be mounted on the bed of a truck and driven to the drill site. The drill parts can be bought from the numerous world-wide companies that make drilling tools or they can be made from readily available scrap steel and local materials.
The hand-powered percussion drill has the final advantage of
requiring a lot of unskilled labor. This encourages the
involvement of many villagers in the building of the well, which
can translate into more involvement with the maintenance of the
well in the future.
Last updated November 06, 2010 by