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Publications by Demotech : 1986, Rope Pumps, a Review of Ten Years Experience
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1986, Rope Pumps, a Review of Ten Years Experience
by Reinder van Tijen
Demotech, design for self-reliance, foundation
Dieren, june 1986
How it started
In 1976 Demotech started working on the idea of the rope pump. At that time the foundation Demotech* had its working quarters at the Royal Tropical Institute in Amsterdam.
A visitor told us that improved self made water lifting devices for certain villages in the Air-mountains in Niger in Africa would be very important: many would have to abandon their land without proper means for irrigation.
We made a design for a pump and experimented in our workshop in Amsterdam. The principle of the chain-and-washer pump seemed to be the best starting-point. We first made a pump-rope with tiny rubber buckets attached to it, driven by a wheel made of wooden sticks. A locally woven cotton belt, with rubber buckets sewn into it, was an other idea. This belt-pump indeed worked wonderfully.....but only on the test-site in Amsterdam!
Reality
Reality in Burkina Faso in Africa proved otherwise. Sufficiently strong canvas belts could not be obtained and if purchased, would be too expensive. So we had to start anew. We had the opportunity to study a certain type of chain-and-washer pump, installed on a well in a small village: What worked well and what didn't?
One good thing was that everybody could clearly see how the pump functioned, another that the circular movement of the drive was more reliable than the customary up-and-down movement of other types of pumps.
Less satisfying was the rather heavy weight of the water-column, hanging on the chain in the large diameter PVC pump-pipe (about 50 kg). This caused a slipping and choking over the driving drum, so the chain and washers wore out rapidly.
We therefore experimented again with the use of a rope instead of a chain. We also tried to reduce the strain on the mechanism (to less than 10 kgs) by using a PVC-pipe with a smaller diameter and this also reduced the cost. The two major problems that had to be solved now were how to get grip on the rope and how to guide the pump-rope into the pump-pipe.
Grip on the rope
The wet slippery nylon rope with the little plungers, set at rather irregular distances, had to be put into motion by a wheel with a much larger diameter. This rope should not slip over or stick to the wheel and had to be returning into the well without any pre-tension. We succeeded by making our drive-wheel from the SIDES of a car tyre. The sides were cut out and put against each other with the OUTSIDES facing each other. If the stiff heels of the two rubber rings were pressed and clamped together, the outer parts bent outwards and formed a V-shaped groove with slack edges.
This turned out to be the big trick! The sharp groove between the rubber rings holds the smooth rope without slipping or sticking to the groove and without any pre-tension being necessary. The slack edges shape themselves around the tiny plungers on the pump-rope, without much force that eventually could damage them.
In practice, a car tyre of 13 inch will do best, although 14 and 15 inch tyres can also be used. The tread of the tyre may be torn to pieces as long as the sides are still whole.
The bottom-block
The second major problem is: to find a reliable solution for guiding back the pump-rope into the pump-pipe, down in the well, below water level. This proves to be no problem with the chain-pump. The heavy chain hangs in a loop, which ensures the chain to go straight up into the pump-pipe. The rope with the plungers, however, does indeed cause problems. It just hangs loose down, sways back and forth, can wind itself around the pump-pipe, and the plungers can get stuck behind protruding parts of the well lining.
These problems must be prevented with a well designed inlet guideblock, attached to the bottom end of the pump-pipe: the bottom-block. If the bottom block is well made, the pump rope with the plungers will last for more than a year. If the bottom block is poorly made, the rope will be worn out in a few months and can get stuck. It is difficult to see down in the well why and where the problems occur. After many experiments, it was most appropriate to make the bottom-block out of one piece of wood, if needed weighted down with a stone.
These are by no means the only problems that needed to be solved. During the ten years of development we gathered a number of solutions for these problems, which were appropriate for most situations, that were encountered. Figure 2 indicates all the parts of this type of rope pump.
DESIGN SPECIFICATIONS
The size of the PVC pump-pipe
It is essential to realize that the size of the PVC pump-pipe is related to the depth of the well. A deeper well needs a smaller diameter PVC-pipe. A more shallow well must get a larger size. The correct size can be derived from the WEIGHT of the water-column inside the PVC-pipe.
The water-column is supported by the plungers and will be pulled up by the rope. As long as this water-column weighs less than 7 kg., it is easy to rotate the crank. A simple calculation gives the following pipe-sizes in relation to well depth:
a pipe of 2" (50mm) for wells up to 5m depth.
a pipe of 1.25" (32mm) for wells from 5m up to 13m depth.
a pipe of 1" (25mm) for wells from 13m up to 21m depth.
The amount of water that comes up depends on two conditions:
How well the plungers fit into the pipe.
How fast the pump wheel is rotated.
The clearence of the plungers
The plungers on the pump-rope can be designed in many ways, but it is essential that they move with some clearance through the pump-pipe. This means that water will leak down and at times even stream down along the plungers. When the pump wheel is rotated very slowly no water comes up as it leaks down faster than it is pumped up. When turning a little faster, the water fills the pipe, but it just does not yet flow out. In this case the upward speed of the pump-rope is equal to the leak-down speed of the water. By counting the revolutions of the crank, the leak down speed can be determined. The leak-down speed must not to be less than 10 cm/sec and must not be more, because of wear or by bad workmanship, than 50 cm/sec. The amount of water given by the pump varies between 50 and 90 percent of the theoretical maximum. fig. 3
Right dimensions for pumping comfort
- Although called a hand-pump, the arms, shoulders, back and legs join in the pump movement.
- Pumping becomes very tiring if the wheel is positioned too high or if the crank is too short. It is best when the axle of the pump wheel rotates about 1m (40") above the ground.
- The best length of the crank is 27cm (11").
- If a 13" car tyre is used to make the rubber pully, the pump rope runs on a diameter of 45 cm (18"). It is most comfortable to turn the pump wheel about 40 revolutions per minute. This results in a rope-speed of about 1 m/sec. Most people can maintain this for sometime.
- The pumping yields for the above relationships are given in Table 1.
Table 1 - PUMPING-YIELD |
|
Depth of the well
13m upto 21m
5m to 13m
2m to 5m |
Outside diameter of
the PVC-pipe
25mm
32mm
50mm
|
How many buckets
of 10 litre per minute
one bucket (10 litre)
two buckets (20 litre)
six buckets (60l)* |
* very useful for irrigation of gardens. |
|
Finally, it is important to select the pipe-diameter on what the users themselves regard as a fair average between light cranking and pumping little water or heavier cranking and pumping more water. The opinion of older people and children should come first.
The cost of the pump
A craftsman in Java charges about 30.000 Rp (27 US $) for pump and cover. The cost of materials is about half of this price. The common alternative of two buckets, a rope and a pully cost about 7.000 Rp (6 US $). It takes three to five days to make and install the pump and the cover on a well up to 25m deep.
Pumping problems and maintainance
Too heavy cranking can be caused by:
difficult movement of one or more plungers in the pump-pipe, for example in a PVC-pipe connection.
too much tension on the pump-rope causing wear against the bottom block.
parts of the pump getting loose.
These problems can easily be overcome with some care and know-how. However, as the users still have little experience with its maintenance, in practice these problems impair the functioning of the pump. The recent manual of this pump can easily be copied by the owner. This may enhance future maintenance of the pump.
Different applications
The rope pump can be adapted for different applications. It may be used in bore holes to a depth of up to 70 meters. In this case a second PVC-pipe is used to guide the pump rope down into the bore hole to a specially designed bottom-block. The rope pump can pump along a slope from a river or pont for irrigation purposes. The pump can be driven by a windmill, by animal traction, or by an electric motor. With our pump PVC-pipe and nylon rope can sometimes be replaced by other materials. Demotech has done research on these and other applications and will publish this material in due time
IN DIALOGUE WITH THE USER
What is "Appropriate"?
Apart from trying to improve the concept and the construction details, we tried to improve the method of information-transfer and determine how this could serve best the interest of the user in a developing country. The question of what can be called "improvement" is similar to the key-question: "What is Appropiate Technology?(AT)".
For Demotech, AT means careful re-design or innovation, based on local and traditional technology, to be realised with local means only. This must lead to a permanent and valuable improvement for its users and through information-transfer also for other potential users.
Local technology
Local technology should not be regarded as obsolete, but instead it is the most practical way of solving a problem on the spot! We learned in Thailand how wood can be worked effectively with a cutlass; in Ghana how iron nails can be replaced properly by wooden pegs; in Marocco how iron sheets can easily be cut and formed with accuracy by using a small axe.
Is this "Appropriate"?
On Java a jounalist reported the rope pump had become very popular. We retraced 128 of them. It became clear what people expect of the pumps and how the pumps are being treated and used. These pumps had been introduced by Indonesian NGOs, and were made by the user himself or by craftsmen who sold and installed a few dozen.
"To pump people"
The NGOs (Non-Governmental Organisations) have often introduced the rope pump to start communication with the people. They instruct a group of people in a few days to make a rope pump for themselves. When they are pleased to see the good results of their work, they may consider other nagging problems which can also be solved by their own activities. The rope pump then ceases to be important...
Such problems, where an AT-solution might be suitable, could be housing or transport of vegetables to the market-place. However in most cases the problems won't be technical. The experience of collaboration with the rope pumps may result in an improvement or at least, in a new way of dealing with the problems. Student-NGO Mandiri from Bandung calls this: "To pump people".
Constructing the rope pump may have given the makers an increased self confidence. Anton Sudjarwo, of the Indonesian organisation for village development "Dian-Desa", said: "More important than the rope pump, is that it stimulates the imagination of the people......that they have been discussing the subject the whole night....."
In an Indian village in Peru the people were proud, they finally had accomplished something, that the Mestise (higher class) had not been able to do. In Java, a craftsman making pumps will like to tell you that he has invented the rope pump himself!
The application of the rope pump is finding it's own way. If the introduction has been done well, it always will inspire a few people to make them, for their own use or for a living.
Out of use: one third.
During our visit to Java, we found rope pumps that were abandoned for numerous reasons. For instance the government recently had dug an irrigation canal or waterworks were established nearby. Once, the government had supplied free Dragon pumps.
But it happens more often that the pump is badly made. It stays a constant nuisance until it is finally put out of use. In the latter case the pump-rope could be found serving as a clothes-line!
Organisations gave free rope pumps. These presents were welcomed, but why didn't these organisations also give maintenance for free? We noticed that bought pumps were less frequently out of use than the donated pumps! Out of the 128 inspected rope pumps, 42 were out of use: about one-third.
Working: two third
More than two-third of the number of inspected rope pumps which were built after our introduction on Java in 1980 are still in use today. The craftsman or the owner himself takes care of all the repairs. As no nut-and-bolt or welded connections are used in our design, repairs are always possible with a bit of wire or rope. Teaching tool development-workers often were embarrassed to introduce a construction which they felt to be too primitive. They "improved" the basic design by using welding work or adding "extras". Mostly this leads to almost insolvable maintenance-problems for the local users. The user then looses confidence in development work as a tool to improve his livelihood.
The pump must have a functional appearance, which is not to be confused with "primitive". The design offers only the BASIC information for its construction, use and propagation. It is a guide for its method of construction, it is a "teaching tool".
Whoever wants to build the pump, likes to decide for himself what his needs are and how the pump will look. For example, in a village in Java pumps are mounted on concrete well-covers which are beautifully finished. On the other hand, Thai farmers were only interested in the water to irrigate their vegetables. They have made sturdy, but very rough wooden constructions. In a village in Ghana, there was a problem of dirty water that could flow back into the bore hole after heavy rainfall. The problem was solved by laying bricks to house the pump and create a raised platform for the one who is pumping. The construction of pumps by the users is a rich source of inspiration to us. The same problems that we encountered during the design phase, have also been worked on by a self-builder somewhere in a village. It's always a surprise to see his solution! But, as the self-builder doesn't have the opportunity to develop his ideas and to pass them on, we can do that for him. Many improvements on the rope pump arose in this way.
Construction manuals
As the design of the rope-pump proved to be reliable, information about it, has to become available through construction-manuals. We found it very difficult to design a manual that effectively transfers the information to its future user. Just making a neat little book didn't do. As it takes a lot of time and expertise, such a booklet tends to become too expensive and for that reason stays in cupboards. Instruction books almost always come in the wrong language and contain mistakes, repeated year after year.... A special problem is that a group of people can't be instructed by using only one little booklet and practical oriented people may find the information from such books not really adapted to their situation.
"Looking together"
What did work, then? Understanding drawings didn't cause problems. Even sketchy illustrations were understood, if people were really interested and knew the general context. It turned out to be important, for people to have the opportunity to look together at the drawings and talk about them.
Good illustrations were needed to point out the scale and action in a manual. The drawing of a well-cover that is lifted by many persons, will make clear at first sight that this is heavy work which will take many people.
Our method to make these drawings is to project slides or negatives against the bottom of a glass pane. By tracing the images on a piece of paper, the right perspective will be obtained. The drawing can be kept simple. Everything of no importance is left out. When we worked in a village, such drawings were sometimes copied by bystanders in notebooks.
Involving people as a group
As we want to involve groups in the discussions around the construction of the pump, we have now designed the manual in a series of loose sheets of A4-size paper with illustrations and text. The drawings can be attached one after another to the wall of a village-house or school. The front of each sheet shows how to make it, what to do, what tools are needed and information on measures. The reverse-side gives the instructor background information: How to organize the course on pump construction; how to prevent mistakes and more detailed technical information. On the reverse-side cases are described of rope pumps being made elsewhere, which were succesful or not, and why. This information must contain a healthy criticism. It also has to mention when not to apply a rope pump, thus the organisation introducing the pump, won't have to learn by bitter experience.
* "Demotech, design for self-reliance" was founded in 1974. Its task is to work out designs to support self-reliance in the informal sectors of modern and traditional economies. At the same time, research is carried out on effective information transfer to future users with demonstrations, small exibitions, in-situ training and methods to design and use construction manuals.
Illustration:
drive wheel / bearing-block / crank / delivery gutter / PVC pump pipe with pump rope and connection / bottom block
Publications by Demotech : 1986, Rope Pumps, a Review of Ten Years Experience
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