| Animal Powered Systems |
|7. Profiles .|
By tradition, Delous are used in Northern Africa' the Sahel, the Near East, Persia and India (where they are referred to as "motes". The basic components of a Delou are a water vessel, a hoisting rope and a guide for the rope.
In its simplest form, the Delou is used by nomads in the Sahel region. A simple leather bag or tube from a truck tire (cut open and sealed off on one end) serves as the water vessel. The rope guide consists of a tree limb mounted at the rim of the well. The rope pulled by the draft animal (ox, horse or camel) slides back and forth over the limb. The friction between the rope and the limb (intensified by sand) wastes part of the animal's energy and soon abrades the rope. Often enough, the rope snaps, and the bag drops into the well. Retrieving the bag is a risky operation, since the sides of traditional wells are not secured.
Even a simple pulley can be of great help in improving the efficiency to a remarkable extent.
It can be made of wood in the traditional fashion or from metal. Since most nomads carry their own pulleys with them, they have to be portable, i.e. not too bulky or heavy.
Permanently installed pulleys have not proved very successful, especially when rollertype devices are used. They are often used for carrying out several drawing operations at the same time. As shown in, the pulleys are literally sawn to pieces by the sandy rope within a few months and are then replaced by the traditional limbs.
Technically superior versions of the Delou were able to develop in areas where they are used for purposes of irrigation by sedentary populations (Northern Africa, Persia, India). Apart from a stationary framework with sturdy pulleys, such Delous feature means for automatic emptying of the water bag and a more efficient utilization of the applied tractive power. The framework consists of either a simple structure of wooden beams, brickwork, or a combination of the two. It is often equipped with pulleys for two simultaneous but. independent water-raising operations and is accordingly robust.
For the purposes of automatic emptying, the bottom end of the water bag has a tubular extension with a rope attached at the end. The other end of the rope (like the pulling rope) is fastened to the yoke of the draft animal. The drover keeps it taut during the raising process, so that the tube buckles over and seals off the water bag. When the bag arrives at the mouth of the well, the drover pulls on the rope so that the water runs out into the channel at the well's rim and flows into the irrigation ditch or watering trough.
The most laborious improvement over the nomadic version of the Delou is the construction of an inclined plane for the animal's pulling path in order to more uniformly distribute the draft animal's strength over the full work cycle: Part of the energy accumulated by the animal by climbing up the slope can then be used to its own advantage on the way back down. It has not yet been determined to just what extent the considerable variance in the angle of the slope (10° - 30°) is attributable to less-than-optimum planning or just the opposite, namely quite specific optimizing, e.g. in deference to different breeds of draft animals.
At any rate, rhythmic motion is maintained. Also, at the lower end of the inclined plane (that is, upon completion of the pulling phase), the animal is allowed to rest for a little while.
Occasionally, feeding troughs are provided there.
An advanced version of the Delou - also aimed at improving tractive-power utilization by avoiding energy wastage on the draft animal's way back to the well, is the so-called "GuÃ©roult".
Originally developed by the "Institut SÃ©nÃ©galais de la Recherche Agronomique", about ten such systems have been installed in Senegal since the early seventies by PÃ¨re Lebegue of "Mission Catholique de Gossas", the Senegalese Appropriate Technology Group ENDA, and the "Institut Technologique Dello".
The GuÃ©roult has two buckets with a volume of about 501 each that are alternately filled and emptied. They are fastened to the ends of a steel cable with a full length amounting to some 3 1/2 times the depth of the well. The cable is guided by two pulleys over the mouth of the well and a third pulley mounted on a framework at a distance from the well that roughly corresponds to the well depth. The team of oxen (GuÃ©roults are usually operated as spanrigs) is harnessed to the middle of the cable, so that one raising phase each is carried out on their way back and forth.
An important advantage of the GuÃ©roult as compared to the Delou is that the 'cable (or rope) never drags along the ground, which prevents pollution of the well. This is thanks to the heavy weight of the iron water buckets (40 kg), which keeps the cable taut. On the other hand, the heavy buckets also constitute one of the disadvantages of the GuÃ©roult, namely the extensive wear and tear to which the wall of the well is subjected through their constant bumping.
That problem has been greatly alleviated by an improvement introduced by PÃ¨re Lebegue (a foot valve). In addition, recent developmental progress at the "Institut Technologique Dello" has contributed much to reducing the cost of installation and maintenance. Nonetheless, since the entire construction is made of steel, the cost of a GuÃ©roult still exceeds the financial means of the average Senegalese farmer.
Recent investigations also indicate that women can expect to reap little of the advantages of a GuÃ©roult: Since women have no say over the family's draft oxen, the mere existence of a GuÃ©roult on the farm may tend to increase a woman's dependence on her well-to-do husband (who owns the oxen).
The "ManÃ¨ge du Jardinier".
The ManÃ¨ge du Jardinier also has two delivery vessels for alternate raising and lowering.
Each bucket is tied to the end of a rope, and each rope runs over its own pulley at the mouth of the well. and continues on to a third, common pulley (a vertical drum), where one of them is wound up while the other is payed out. As in the case of a continuous system, the draft animal moves along a circular track, but has to be turned or reharnessed after every raising of a bucket (as is the case in an intermittent system) in order to backtrack along the same circular path.
Since the drum and the circle described by the animal are of different diameters the ManÃ¨ge du Jardinier also constitutes a simple gear unit. Depending on the ratio between the two diameters, the tractive power is in creased and the speed decreased by a certain amount.
This system is especially suitable for lifting heavy loads. While illustrates as well- building application' the system is equally suitable for water-raising purposes, in which case relatively large delivery vessels are required. For a drum diameter of 1 m, a circular track diameter of 6 m, and tractive power of 30 kp, the vessel volume would have to be approx. 160 l (with due account for the weight of the rope). Accordingly, the framework, pulleys and ropes must all be sturdier than for a Delou or GuÃ¨roult. On the other hand, the time lost during reharnessing or turning is less signifi cant, because the raising cycle for each bucket is longer. The system does not require much space, and one person is usually sufficient for its operation.
The ManÃ¨ge du Jardinier is well suited for low tractive power and relatively large depths. For example, pertinent literature contains a reference to such a system in a fortress in Palestine where water was raised from a 55 m deep well by a donkey, whereby a special device enabled automatic emptying of the bucket, and the donkey is said to have reversed direction on his own whenever it heard the sound of the bucket being emptied.
This water-raising arrangement was designed by British colonial engineers just after the turn of the century. It is also frequently referred to as "Mote de Ceylan" (after the region in which it has become most popular). And since it combines the intermittent raising and emptying of buckets with the continuous circular motion of draft animals, it is sometimes called a "circular mote".
Stoney's mote is a simple, practical application of one of the basic elements of engineering: the crank. Cranks are used in engineering wherever rotational motion has to be converted to linear back-and forth motion (or vice-versa), be it in a bicycle, an internalcombustion engine, or whatever. In the case at hand, the circular motion of a draft animal is converted into the rhythmic alternate raising and lowering of two delivery vessels by attaching the center of the pulling rope or cable to an off-canter point on the drawbar and running the two half lengths to the buckets via two pulleys each - one each over the mouth of the well, and one each on (either) side of the circular path.
Figure below illustrates the basic principle of function and automatic filling and emptying of the buckets. The drawing depth of such a simple circular mote is equal to twice the distance between the pivotal point of the drawbar and the point at which the pulling rope is attached to the drawbar, and is thus limited to 5-8 meters. As long as the buckets are emptied automatically - and rapidly enough - the animal needs not stop at that point, but should at least slow down somewhat, since the geometry of the arrangement is such that the buckets move slowly in the vicinity of their reversing points, i.e. for filling and emptying. They move most rapidly about one-third of the way through the raising/lowering phase.
In each such instance, i.e. when the cable is tangent to the circle defined by its point of attachment, the animal has to deliver the most tractive power. In other words, due to the intermittent delivery, the required tractive effort varies from moment to moment. It increases from 0 to maximum during the first third of each drawing phase and then gradually drops off to 0 again at the end of the phase. Thus, as the animal traverses: a full circle, the requisite pull swings twice from 0 to 100%. The maximum pull depends on the geometry of the drawbar structure and can amount to any value, between 50 and 100% of the weight of a full bucket.
Due to the varying tractive power in combination with the unidirectional, circular path described by the draft animal, Stoney's mote may be regarded as a cross between an intermittent and a continuous water-raising device.
In the elaborate version of Stoney's mote in Sri Lankam, the drawbar is equipped with a supporting wheel and a seat for the drover. A block and tackle arrangement is used to quadruple the drawing depth. The prototype of a simplified circular mote has recently been developed by the "Institut Technologique Dello" in cooperation with GATE. It is made almost entirely of wood, and the chains have been replaced by nylon ropes. Conceivable measures aimed at smoothing out the tractive power curve (more buckets, counterweights, etc.) have not yet been tested in the field. Presupposing a satisfactory arrangement for automatic emptying of the buckets, Stoney's mote could well be one of the most attractive solutions for drawing depths of about 6 m.
The "ManÃ¨ge Sahores".
The ManÃ¨ge Sahores is a modernized version of the circular mote for large drawing depths.
The buckets have been replaced by a pump and a counterweight (figure).
This water-raising rig was designed by the French engineer Jean Sahores, who since the mid '70s has been working on simple wind-driven, hand-operated pumps, primarily for use in the Sahel. The overriding principle behind all of his developments is that the appliances can be built and maintained by local craftsmen. In the case of the pumps, this is achieved by using plastic pipes that can even be cut and processed by the farmers themselves.
The ManÃ¨ge Sahores employs such a pump. The maximum achievable pumping depth is presently about 15 meters, though 25 m would appear feasible.
ManÃ¨ge-Sahores systems are presently under" going field testing by Jean Sahores himself the "Institut Technologique Dello" and at several locations in Senegal.
In a GTZ project in Southern Senegal, a pro" totype ManÃ¨ge Sahores with a drawing depth of about 10 m has already achieved delivery volumes on the order of 2.3 m3/h. The donkey providing the power for system operation puts in a 4-6 hour workday.
Waterwheels, in all their many variations, are regarded as classic examples of Arabian/lslamic culture as applied to the task of raising water. Invented in ancient times, preserved and sophisticated in Arabia, rediscovered first in Southern Europe and then in Central Europe, waterwheels are typical representatives of a polyglot, international technology.
"Fetching up the waters" was a major discipline in the classic natural sciences of Arabia.
Numerous, voluminous reference works offer quite practical instructions on how to locate groundwater, how to judge the quality of well water, etc., as well as a host of more esoteric reflections, such as the hope accompanying the many deliberations on how to improve waterwheels to the point of perfection, namely to turn them into "per petua mobilia".
Thus, in Arabian-lslamic culture, waterwheels are far more than mere technical objects.
They are so deeply rooted there that they have given rise to a literary genre all of their own - "waterwheel poetry" - in which the creaking and groaning of the wooden wheels is besting and from which they have derived such poetic names as Noria ("the wailing one") and Hanana ("the moaning one"). Even a sober-minded French colonial engineer was so caught up by their magic at the turn of the century that the report he filed included the poetic remark: "The Saqia announces its presence from afar; its incessant moaning and plaintive groaning pierce the quietude of the plain, trouble the peace of the night, and underline the cost and effort that man must pay for bringing fertility to the arid soil." The quality of a waterwheel, then, may be judged as much by the sound it makes as by its efficiency. Similar irrational factors surely play, or have played? a like role in numerous other innovative processes. Aware of that fact, many industrialists enlist the aid of psychologists and designers. Unfortunately and all-too-frequently, scholars of "Appropriate Technologies" tend to rely on a line of argumentation that only stresses technical efficiency and cost effectiveness.
Waterwheels can be classified either by their actual mode of operation and achievable drawing depth or by the type of power transmission they employ, whereby the latter serves in redirecting the animal's rotary motion (horizontal plane) onto the waterwheel (vertical plane).
A wide variety of wooden angular gears are used, e.g. two star wheels of approximately equal size in Egypt, or a horizontal lantern wheel in combination with a vertical cog wheel in Spain and Morocco.
The greatest drawing depths can be achieved with potgarlands ("Noria": 5-20 m, figure below), followed by bucket wheels with the water vessels arranged around or integrated into the wheel perimeter ("Tabout": 2-4 m, figure below) and spiral wheels ("Tympan": 0.3 - 2.5 m, figure below).
With but a single exception, all waterwheels have the same disadvantage: they "overlift" the water, i.e. they raise the water to a higher level than necessary. This is particularly wasteful (with regard to energy input) when the difference between the discharge height and the outflow level is of the same magnitude as the drawing depth, i.e. for shallow drawing depths.
Spiral wheels are the only version with which overlift can be avoided, since that is the only design that raises the water inside of the wheel radius (like an Archimedes' screw) and discharges it through the wheel axis. First figure - taken from Jakob Leupolt's `'Muhlenbuch" (published in 1728) - includes two examples of the spiral-wheel principle (nos. 10 and 11).
The most significant practical example of a "Noria" is the "Moorish Noria" which, in its original all-wood form, can still be found in Morocco, where it is called the "Sepia". An improved version with certain components made of metal is still in use on the Iberian Peninsula and on Spain's Mediterranean islands.
The Senias of Beni Boufrah valley in Northern Morocco have drawing depths of between 10 m and 16 m and are capable of irrigating vegetable gardens ranging in size from 1000 m2 to 5000 m2 They are operated almost exclusively by donkeypower, with the donkeys working up to 8 hours per day. Built by the farmers themselves, the Senias have such high friction losses that their efficiency is extremely low (roughly 255%. The improved Spanish version, however, seems to achieve up to 50% efficiency.
With a total number of some 400000 waterwheels (Saqias), Egypt is still one of the classic waterwheel regions. Saqias, though, are rarely used for watering small vegetable patches, but primarily for irrigating large fields of grain. On the average, a single saqia is used for about 6 hectares (~15 acres). This is made possible by the high ground water level (0.3 - 2.0 m), together with more powerful draft animals (cattle) and more efficient designs (usually a spiral wheel and cast-iron bevel gears). While some wooden gears and less-efficient types of waterwheels (Tabout or Zawafa) are still to be found, Egypt is still a shining example of the fact that - given the appropriate political environment - a highly developed handicraft trade will usually be capable of creatively sophisticating its own traditional techniques through the introduction of new materials.
Animal-Powered Industrial Pumps
Around the turn of the century, dozens of European and American firms made or marketed industrially manufactured, animalpowered pumps. In most cases, universal power gears were combined with pumps of different maces of operation. Depending on the requisite drawing depth, the pump would be of the piston, diaphragm, rag or centrifugal type.
Their market niche, apart from the colonies of that period, mainly comprised small to medium-sized farms in metropolitan areas. In rural France, for example, some such pumps remained in use until the 1940s.
Like most other machines of the time, animal-powered pumps were very heavy, sturdy appliances. While importance was attached to durability and ease of maintenance, it was not intended to provide for the manufacturing of such machines in the colonies. Since no empirical data are available on the practical use of these pumps, the suppliers' old advertising brochures and catalogues are the only sources of performance data. In most cases, though, such material is full of inaccuracies and exaggerations, as well as being generally based on operation by heavy draft horses. Thus, the capacity ratings ranging from 300 to 400 WW, have to be taken with a grain of salt, even though such pumps really could work at higher efficiencies - as long as they are properly operated and maintained than would be attainable with the traditional systems described above.
The second-best sales argument (just behind the performance data) in the advertising brochures was the more-or-less "quiet" running of animal-powered pumps: But such pumps, especially the piston and diaphragm versions, required flywheels, belt drives or intermediate gears (for transmission to higher speed) to protect the animal from load fluctuations and shocks resulting from the intermittent principle of operation. In addition, the number of cylinders was often increased, so that three-cylinder animal-powered pumps were no rarity. No problems in this respect are encountered with the continuous-action rag pump, which, despite its relatively high maintenance requirement, was quite popular at that time.
Today, such animal-powered rag pumps are available from the Indian company Cossul. The delivery rating of 10 to 15 m3/h for a drawing depth of 13 m (corresponding to approx. 400 WW) seems to be somewhat overly optimistic. The current prices and supply details were not known at this printing.
A very revealing case history on the use of industrial animal-powered pumps in developing countries was filed in 1983 by Pierre Guillaud Brandon: Between 1962 and 1966, the "Service des Ã©quipements ruraux 83" in Morocco installed a large number of animalpowered pumps of a type designed and manufactured by the Gillaud Co. of Casablanca. The aim was to improve the potable water supply in remote villages. The pumps were designed for well depths of anywhere from 10 m to 77 m, i.e. depths for which the traditional Moroccan Noria could not be employed. After several trial installations, a rather complicated version with a double- action pump, a 45-kg flywheel and a progressive transmission was decided on. Though the initial cost of such a pump was as high as that of a motor-driven pump with a much higher capacity, the operating costs were so low that all cost-effectiveness analyses came to the same conclusion: the animal-powered pump was, in the long run, considerably cheaper than a motor-driven pump. Then, in 1970, a survey revealed that only 25 of the pumps had achieved an average service life of about 15 000 hours (approx. 3 500 operating hours per year). The vast majority of the pumps was out of service, mostly due to relatively minor breakdowns (broken linkage, jammed transmission, etc.), that the users did not have the means to repair.
In his review assessment, Pierre Guillaud Brandon came to the conclusion that the anticipated maintainability was unachievable in spite of all the engineering effort that had been put into the design. The degree of reliability requisite to a safe supply of potable water could only have been warranted by a team of maintenance specialists. That, in turn, would have seriously diminished the cost advantage and been too expensive for the users. Thus, it should come as no surprise to the reader to learn that the last pump that was still in operation in 1983 was found to be in the hands of an "entrepreneur" who sells the water he raises to the village inhabitants. This example illustrates quite clearly that the efficiency advantage offered by industrially manufactured pumps for animal-power operation can be lost very quickly due to expensive, complicated repairs.