Advantages of the Percussion Drill
Percussion drills can be used in many types of earth: clay, sand, rock, and soil. Percussion drills usually do as well or better than other types of drills in most types of soil and is the best hand-powered method for drilling rock.
Percussion drills have been used to drill wells that are thousands of feet deep, though they are more commonly used for wells from 30 to 250 feet deep.
The bore holes made by percussion drills are much easier to protect from contamination than their counterpart, the hand dug well. This is because the hole they make is smaller and easier to seal so that surface water cannot flow back into the well once the casing has been installed.
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 a pick axe and shovel. But when digging and drilling costs are compared side-by-side, the percussion drill proves remarkably cheaper.
DRILLING AND FINISHING TWELVE WELLS
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 makes it easier to make the well and protect it from contamination. On the other hand, such a narrow hole 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 Nations 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. (It is possible that drilled wells with 6" 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 well hand-drilled in China in 1923 was over 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.
It is sad to note that hand-powered percussion, like many other time-tested but low-tech well making techniques, has not been widely utilized in the developing world. (See the 1990 paper: Appropriate Technology Strategies for Rural Water Development After the Decade for more background.)
There remain few current examples of hand-powered percussion drilling being used around the world. This is despite the fact that there exists a ever-shrinking number of older drillers who had contact with these techniques in their youth. It is likely that percussion drills have not been favored by organizations promoting appropriate technology because of the percussion drills 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 tools, the 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 in the rural areas.
But the simple 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 utilizing a lot of unskilled labor. This encourages the involvement of many villagers in the building of the well -- which can translate into their being more involved with maintaining the well in the future.