The story of a waterwheel
Waterwheels have been used since ancient times to grind corn and also to raise water. The great waterwheels of Hama in Syria have raised water for over a thousand years. They serve as superb examples of a technology so elegantly simple that it becomes totally dependable. Flowing water was used to turn the wheel and water held in buckets on the rim was lifted to great heights to spill over into channels which irrigated the land further away. These great wheels where often built to huge proportions, because water was raised on their rims. Some in the Middle East were 100 ft in diameter. Water mills were common in Europe and elsewhere as a reliable source of energy and they were put to many uses. Attempts to use the power of the wheel to raise water above the level of the rim have often involved the use valves, pistons and levers, but none of these match the elegant simplicity of the wheel.
Huge waterwheel in Syria used to pump water for irrigation
The waterwheels of Mazowe
There is another little story, almost forgotten, that could be told of a few waterwheels that were built during 1979 in the Mazowe area, about 30 kms north of Harare, Zimbabwe, then known as Salisbury. These waterwheels raised water to well above the level of the wheel rim, under pressure without the use of valves or pistons of any type. The pump consisted of no more than a coiled pipe open at both ends. Water was raised as if by magic, under pressure by the development of a series of air locks held in these spiral tubes attached to the wheel.
This was far from an obvious concept. But the idea came to me during our testing of a biogas tank fitted beneath a Blair toilet at the Henderson school (see later). We built our first “spiral tube” waterwheel pump at Henderson Research Station on 18th May 1979. I attached it to a small waterwheel fitted over a water channel which supplied the fish ponds at Henderson Research Station. In this first working prototype 20 metres of 25mm plastic pipe were attached to 2 metre diameter wheel which was rotated by the flow of water. It delivered about 1.3 litres of water every time the wheel turned. We used the wheel to pump water up to a tank. The small 2 metre wheel Henderson operated almost continuously without maintenance for about 2 years delivering about 7000 litres of water daily to a header tank near the canal which fed water into a purification system. Very little maintenance was required.
The first prototype and operational spiral tube waterwheel pump at Henderson
Testing the first waterwheel pump at Henderson – water is coming out of the pipe well above our heads!
The concept was so successful that later that year in October, we build a 4 metre diameter wheel which was fitted on the large irrigation canal at the Mazowe Citrus Estates. It also worked like a treat and I fitted two spiral tubes, one on each side of the wheel to increase the flow of water. Readings taken on this wheel revealed that 4752 litres of water could be delivered to axle level per hour and 3697 litres of water could be delivered per hour to a height of 8 metres above the water level. We measured a canal flow rate of 1m/sec., canal width of 1.93metres, wheel diameter of 4 metres, number of wheel paddles was 16. The paddle size was 600mm X 600mm, number of spiral coils was 2 with 3 spirals on each side. The diameter of the pipe in the coils was 50mm and made of low pressure polyethylene pipe. The wheel turned at 4.2 revolutions per minute when water was delivered at axle level and 3.21 revs/min when water was pumped to 8m.
Assembling and fitting the 4 metre diameter waterwheel at Mazowe
Parts of the wheel were first made up in the Blair Laboratories. They were the taken to the irrigation canal at Mazowe and assembled. The wheel was made up mostly of plywood and pine beams. The axle was made from 75mm steel pipe, reduced through reducing sockets to 50mm pipe. The axle was mounted through two sealed ball bearings mounted on the two brick built supports at the side of the canal.
Wheel upright and spiral tube fitted. About 35 meters of 50mm polyethylene pipe were coiled on each side of the pump. The pipes were threaded through holes made in the paddles. The two water collectors were made of 150mm PVC pipe, each about one metre long. The ends of the innermost coils were connected to the axle through polyethylene elbows.
The waterwheel was impressive – a moment before fitting
Straddling the canal. The brick mounts for the bearings had already been made.
The wheel is mounted. Note the two pipes from the coils going into the axle. This method of linking the pipes to the hollow axle with a galvanised steel cross was not successful. The threads in the pipe were weak points and could not take the strain under the weight of the wheel. The axle was replaced with a single 75mm steel pipe and the water was led into it through an entry point nearer the bearing.
A drum was mounted on an eight metre platform high above the canal. Water and air coming from the coils was led from the axle, through a simple water seal to the vertical pipe which led to the drum. This photo shows the modified water entry point into the axle, to one side.
Painted up the wheel looked very smart.
The axle, water seal and bearings. On the left water is led from the two coiled pipes to a tee piece (on the inner side of the central wheel) through the wooden discs which hold the spokes and then through a bend into a steel tee piece on the main axle. The axle is mounted on a bearing surface. Different bearings were tested. The best were made of sealed ball bearings. A variety of water seals were also tried. This one (RHS) shows a rubber bearing mounted in a PVC sheath. A PVC adaptor attached to the axle passes into the centre of the rubber seal. One side rotates, the other side is static. Bearings always leaked slightly. The rotation of the wheel was slow.
View of the wheel from the drum stand. An impressive site. Note the white PVC pipe
Which is bringing up water from the wheel into the tank above.
The original wheel installed in 1979 was replaced by a replica made of improved timbers in the early 1980’s. This new wheel had larger paddles more closely shaped to the angled walls of the canal. It was generally of a much stronger construction.
Another similar wheel was built on the Mazowe stream by Ron Evans, the farm manager at Henderson Research at the time, with water being led through a wear into a series of half drums fixed to the rim of the wheel. This wheel too was 4 m in diameter. This wheel was made of steel throughout and not of wood like the first wheel. Eventually the original wheel on the Mazowe canal began to break up and a stronger unit was built there a few years later using the original design. It continued to work for many years and may still exist. A similar 3 metre diameter wheel was built for the Ministry of Health stand in 1980 and attracted much interest. A smaller wheel was built by my friend Dr Paul Canter, at the Triangle Sugar Estates It was a smaller diameter about 1m but had many coils and pumped water to quite a height.
Ron Evans and I inspect the all steel wheel at Henderson. It was placed in a wear on the Mazowe stream at Henderson. In this case the water filling the quarter steel drums fitted on the rim turns the wheel and the pipe is arranged in the shape of a coil, not a spiral. The same principles hold true.
Fitting the wheel in the brick built wear at Henderson.
On the left a 3 meter waterwheel built for the 1980 Ministry of Health Trade Fair Stand in Bulawayo, which attracted much interest. Few asked what the waterwheel had to do with health! On the right a smaller waterwheel made by Dr Paul Canter at Triangle Sugar Estates in the Southern Zimbabwe.
Making the wheel and pumps
The wheels were really intended to work in irrigation canals in order to pump water from the canal to a header tank above the canal for domestic use or for irrigation. The waterwheels themselves were made up from a series of wooden or metal paddles attached through spokes of wood, aluminium or steel to a central hollow axle mounted on “pillar block” ball bearings placed on mounts placed either side of the canal. The “spiral tube” water pump itself consisted of a length of plastic pipe so arranged that it formed a spiral fixed to the sides of the wheel. In working wheels two spiral tubes were used and these were horizontally opposed. Water entered each spiral tube through an enlarged pipe which acts as water collector. The collector picked up water as it dipped into the water flowing down the canal – like a scoop. Enough water was picked up to half fill each coil. Thus a core of water was picked up on each revolution of the wheel followed by a core of air. So an alternating series of cores of air and water entered the coils, which passed along the pipe as the coil turned on the wheel. The innermost spiral of the tube delivered water into the wheel axle and there it is was led through a simple water seal to a static rising water pipe to the header tank.
Waterwheel being constructed at the Blair Laboratories, 1979
How does it work ?
The spiral tubes are fixed to the wheel so that the spiral pipes rotate as the wheel itself rotates. The water collector connected to the outermost end of the spiral tube gulps in a good quantity of water as it passes through the canal, and delivers this into the spiral tube as it rises above the canal. This core of water passes through the spiral followed by a core of air as the wheel rotates. A new core of water is formed on every revolution, and a new core of air. Thus a series of cores of water and air are formed within each spiral pipe as the wheel rotates. Both spiral tubes deliver their water and air into the axle of the wheel and there it is led off through a water seal to a static rising pipe, which delivers water to the header tank.
As the wheel revolves a pressure head develops within each coil of the spiral tube, water in the rising coils being higher than in the descending coils. These cores of water in the spiral tube compress the air between them as they travel around the spirals and both water and air are expelled under pressure into the axle. The flow of water up the static rising pipe is also accelerated by the compressed air escaping and expanding from the outlet at the axle of the wheel. This effect also helps to lift water to the header tank.
Diagram of the spiral tube waterwheel pump from the side.
In this view, the canal water is moving from left to right and the wheel is turning in an anti clockwise direction. On each revolution the larger water collector pipe dips into the canal water and lifts up sufficient water to half fill each coil of the spiral pipe. Once the water has been emptied into the outer spiral, air enters the pipe. Cores of water followed by air enter the spiral pipe each time the wheel turns. These cores of water and air make their way from the outer spiral to the inner spiral and then into the axle of the wheel. Water in the ascending spiral pipe is always higher than in the descending pipe. Thus the weight of water held in the pipes on the “leading edge” of the waterwheel is greater than the weight of water held in the “trailing edge” of the waterwheel. The energy in the water falling on the paddles must be sufficient to overcome this weight difference between leading and trailing edges of the wheel.
Tests carried out showed that the highest point to which water could be pumped appeared to depend on the number of spirals in the pipe and the diameter of the spiral. A 2 m diameter spiral tube wheel was able to pump water up to at least 8m with 6 complete coils, the same tube being able to pump water 6m with 4 complete coils and 4m with 2 complete coils. The volume pumped depended on the amount of water picked up and retained by the pipe during each revolution. Several spiral tubes could be fitted to the same wheel, the ideal number being two. With a single spiral, air and water are expelled alternately at the outlet, the pressure heads in each coil developing to their own maximum as the water pressure head in the rising main is at its highest. With two horizontally opposed spirals tubes fitted to a single wheel, air and water rise through the pipe in more regular bursts.
Considerable pumping heads can be achieved if necessary by using an appropriate number of coils on a suitable sized wheel of placed over a canal or river system charged with adequate water power. The power delivered to the paddles must be sufficient to overcome the weight of water held in the rising segments of the spiral and obviously this is a limiting factor. If the weight of water held in the rising coils is much larger than the weight held in the descending coils, the wheel may stop turning if the power delivered to the paddles is insufficient. A balance must be struck between the power delivered by the water on the paddles, the wheel diameter, the pipe size, number of coils, and required head of water delivery. If the number of coils in the spiral is not sufficient to pump water to the desired height, water flows over from one coil to the next. Efficiency is lost. In these wheels constructed, these various factors were worked out before the wheel were constructed.
The great advantage of the system, was that once it was worked out, the mechanics was very simple and reliable. The spiral tube pumps made perfect partners for the wheel and both harmonised with the natural world.
Other work with the spiral tube pump.
When these wheels were designed and built, we had little access to such specific international literature. I searched through volumes at the University to try to find some similar device, but failed to find anything other than the Archimedes screw. A few years later I was in correspondence with Peter Tailer who worked at the Windfarm Museum, Vineyard Haven, Massachusetts, USA. He must have come across the paper I wrote about the spiral tube pump and waterwheels in the Zimbabwe Rhodesia Science News (Volume 13, No. 8. August 1997). He told me that the first spiral pump had been created by a pewterer in Zurich in the year 1746 and an account of it had been published by Thomas Ewbank in 1849 in America. Ewbank reported that pumps of this type had been highly successful and were used in Florence as well as Archanglesky in the latter part of the 18th century. Peter Tailer wrote a manual on spiral pumps of this type in 1986. In this manual he describes not only the complex mathematics of how and why the pump works but also that a certain Peter Morgan of the Blair Research Laboratory, was probably the first person to built a “Wirtz Pump” after it was forgotten and lost for more than a century. In his manual he has written down a part a letter I wrote to him at the time, describing the events which led to my own discovery of the concept. It reads:
………“The spark of the idea jumped when I was adjusting a pipe carrying a gas from a biogas digester we had installed beneath a toilet at the Henderson Research Station near Mazowe. The tank had developed at least one cubic metre of methane, but I could get no gas out of the end of the pipe which led from the digester to the stove nearby. I remember being annoyed by this as it was obvious that a type of airlock had developed in the pipe leading gas from the tank to the outside.
We looked down the toilet hole and I noticed that the pipe has become coiled several times. This was possible because we had allowed quite a lot of pipe to be used to accommodate the up and down movement of the digester gas tank. In earnest I pulled hard on the pipe whilst looking straight at the end of it. The pulling of the pipe released the airlock and I got a face full of very bad smelling mess and gas. Pulling the pipe had released the airlock and gas now flowed freely outward.
From that moment I wondered what could have been going on down there. It was obvious that fluid produced by the digester had built up at the base of the coils to produce airlocks. These had, in effect, held back the gas produced by the digester. I wondered whether the reverse might be true. Could one coil a pipe up, which contained a number of deliberately made airlocks, and develop pressure?
On a later visit to Henderson with my good friend, Peter Gaddie, Blair’s Chief Field Officer at the time, we came across a length of clear plastic pipe laying on the ground. Recalling the experience with the digester, I picked the pipe up and coiled it vertically in my hands with the innermost coil turning to the horizontal and then turned upward to form a vertical segment. I asked Peter to carefully pour water down the vertical pipe. Water passed over each spiral of the tube into the next spiral and then into the next. A series of airlocks had been formed in the pipe. As more coils had water and airlocks formed in them, the level of the water standing in the vertical segment became higher. I rotated the whole spiral tune in my hands and, to my joy, water shot out of the top of the vertical pipe segment above the spiral! This was a most memorable and thrilling experience for Peter and me.
I couldn’t wait to get home and make a bigger version of the model in my kitchen. This too worked well and I found that by adding water to one end of the spiral and rotating it, I could drive water up the vertical pipe segment some distance.
The day following Peter and I built a two meter diameter model at Henderson and fitted it to a waterwheel with paddles attached. The paddle wheel was mounted in a small water channel. The wheel turned and on each turn I arranged for the outer coil to pick up water from the channel. On each turn a core of water followed by a core of air passed into the spiral next to it until finally arriving at the innermost coil. It was then led to a rising pipe through a simple water seal. The effect was thrilling as the system worked so well. Water was fed into a tank and the machine worked for years afterward.
I then developed a horizontally opposed spiral tube pump with two water inlets and two coils feeding a single outlet. This doubled the volume of water produced. From this we then built a much bigger 4 meter diameter wheel on the Mazowe Citrus Estates canal. This pumped an impressive 3697 litres of water per hour to a height of 8 metres above the canal. After two or three years, the wheel was rebuilt of stronger materials where it remains today as reliable as when first built. Several other wheels have since been built in Zimbabwe.” …. Peter Morgan’s work with the Wirtz or spiral pump has been published in a local Zimbabwe science magazine, “Science News,” in VITA News of January, 1983, (Volunteers in Technical assistance) in the United States, and in a Blair Bulletin of 1984.
In the Journal of Hydraulic Research, Vol 22, 1984, G.H. Mortimer and R. Annable, both from Loughborough University, U.K. describe the coil pump – theory and practice. A complex mathematic model is described which I do not understand, but they do refer to my work and paper in Zimbabwe. In this account reference is also made to Mr A Wirtz and his invention of 1746, and also a description by Abraham Rees (1819) in his book “Cyclopaedia of Science and Arts.” These authors state that the origins of the pump may lie much earlier times in China, and also that … though the idea of the coil pump has been gathering dust on some forgotten shelf for centuries, it is worthy of further investigation and development.
My own independent discovery of this ingenious concept was a fulfilling and very satisfying personal experience. Perhaps it is the invention of which I am most proud. But ironically so few waterwheels of this type were every built. In reality it has perhaps a very limited application. But at any scale these spiral tube waterwheel pumps, were both simple and effective and a great joy to watch in action. The story is well worth the telling, for it forms part of an era of personal discovery long ago in that valley of Mazowe.