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close this book Animal Powered Systems
View the document Foreword
View the document 1. Dialogue and Cooperation
View the document 2. Rural Energy - Draft Animals - Animal-Powered Systems
View the document 3. Historical Photos and Illustrations
View the document 4. Animal Energy-Living Energy
View the document 5. Draft Animals: All Work and No Play?
View the document 6. Water-Raising Facilities as Examples for the Efficiency of Animal-Powered Systems
Open this folder and view contents 7. Profiles .
View the document 8. Animal Power plus Local Handicrafts.
Open this folder and view contents 9. Fifteen Comprehensive Theses for the Propagation of Animal-Power Technology.

6. Water-Raising Facilities as Examples for the Efficiency of Animal-Powered Systems

Thanks to a comparative abundance of available information and, above all, to the ease with which their product can be described, water-raising facilities make good subjects for a model description of animal-power efficiency. Both the drawing depth and the delivery volume can be measured with very simple instruments. By comparison, the output ratings of, for instance, oil or grain mills, cannot be limited to quantitative data, but always require a detailed supplementary characterization of both the raw material and the finished product.

The area that can be irrigated with a certain quantity of water is dependent on so many climatic, biological and technical parameters that it would be impossible to characterize a water-raising device in terms of "irrigable area". Thus, a better way of comparing output data would be on the basis of their relative efficiency, i.e. the respective product of drawing depth multiplied by the volume of water that can be raised in a specific period of time. Such ratings can be expressed in terms of "Water Watts" (WW), calculated with the aid of the following equation: Pn (in WW) = 2.7 x water volume (in m3 /h) x drawing depth (in m) In all technical systems, the power input exceeds the useful effect. The useful effect/ power input ratio is referred to as the efficiency of the system and is stated as a percentage. The losses may well exceed the useful effect, in which case the efficiency will amount to less than 50%.

In the case of a draw well, for example, the combined weight of the rope and bucket can easily amount to about the same weight as that of the water raised in a single cycle. In other words, each raising of the bucket involves so much non-productive work that it could even exceed the amount of productive work that is accomplished each time. Such losses can be eliminated by running the rope over a simple pulley mounted on a frame over the mouth of the well and by attaching one bucket each to the two ends of the rope. The weights of the buckets and rope cancel each other out, and the water volume raised with the same amount of work is nearly doubled.

By analogy, the capacity of animal-powered water-raising devices can often be drastically increased without raising the power input (e.g. through better harnessing, adjusting the discharge height of bucket wheels, reducing the friction losses in bearings and gearings.

Accordingly, a complete assessment of a water-raising facility should always include an evaluation of its efficiency, in addition to the indication of drawing depth and volume, i.e. of its useful capacity. That, however, is hardly possible, since it is very difficult to gauge the energy expended by the animal.

The fact that the capacity is indicated in a "technical" form, i.e. in WW, should not lead one to forget that the energy sources for traditional water-raising facilities are living, breathing beings - and thus incalculable. As shown in the examples p. 29 (Schioler, 1981), field data always require detailed interpretation.

The diagram p. 30 surveys the capacity ranges of various types of water-raising facilities driven by animals. The delivery volumes are shown as a function of the respective drawing depth (depth of well). By way of comparison, several types of manually operated water-raising devices are included. The diagram is based on actual cases of practical implementation or observation as described in the literature. The fields of application for individual water-raising facilities are not sharply defined and should not be taken as definite boundaries.

Sample capacity ratings for various types of Persian wheels (in water watts = WW).

Capacity of a Spanish version (Noria de Sangre) drawn by an unattended, exhausted donkey (measured in 1955):

44 WW

Capacity of a Persian wheel drawn by a healthy, unattended bullock (measured in 1979):

90 WW

Capacity of a Persian wheel in Pakistan drawn by two exhausted oxen attended by the farmer:

170 WW

For a short time after the farmer "urged the animals on" (by whipping), the same Persian wheel delivered:

500 WW

Capacity of a Persian wheel in India:

180 WW

Capacity of a Persian wheel near Agra, India, drawn by a rested camel:

240 WW

Capacity of a well-lubricated Persian wheel in India, drawn by an ox held at top speed by an old woman with a whip (measured in 1979):

120 WW

The following capacity ranges are defined in the diagram:

2 - 25 WW Human power

50 - 100 WW Donkeys

100 - 200 WW Oxen, horses, camels

200-400 WW Spanrigs or commercial-type animal-powered water-raising devices

As indicated, the capacity of animal-powered water-raising facilities lies between that of manually operated devices and that of motor-driven pumps. As an example, for a given irrigation perimeter, a "Gueroult" driven by a team of oxen can provide the same useful effect as the work of 10 to 15 people.


Figure


1 Traditional well


2 Archimedian screw


3 Spiral wheel


4 Noria


5 Stoney's Mote


6 Delou


7 Gueroult


8 Industrial gear pump