Spiral water wheel delivers dreamy supply
AS I have no political lobbying or media skills my way of helping the environment campaign is to help those committed to saving forests. My skills lie in the areas of inventing and building. Jill had a 5 hp fire fighting pump she used to refill her concrete water tank every fortnight or so. I first devised an alternative pump using a set of water wheels, which, via chains and cogs that gave a 4:1 step up, drove a small piston pump.
The petrol pump was temperamental and noisy. This improved model was temperamental and oily. It did work quite well but was prone to occasional mechanical failure and there was the possibility of it leaking oil into the pristine Brodribb River. So I got to work on an idea I had seen illustrated as a kids toy. As Jill lives on the upper reaches of the Brodribb River, the small flow in the river was not enough to operate a hydraulic ram pump. The spiral water wheel has the advantage of being environmentally friendly, almost maintenance free, made of basic cheap materials and is relatively easy to make for anyone with a welder.
This positive displacement pump is made from a single length of coiled poly pipe and is designed to be powered by water. The pipe is coiled in a vertical plane and mounted on a horizontal axle. As the paddles rotate the coil of poly pipe above the water, the lower part is immersed. The open end of the coil takes a small gulp of water every time it rotates. An alternating sequence of air and water is driven along the pipe towards the centre of the spiral. Successive coils of pipe lead to a cumulative increase in the pumps pressure output. When a land-fixed pipe is connected to the last and smallest coil, then water can be shifted to a higher point, such as a dam or a tank. In this case, Jills tank is about 16 metres above the river.
Paddles and coils
The set of undershot paddle wheels (powered from water flowing below, not from water dropping onto the wheels from above) drives the whole show. This is one of the oldest and simplest forms of motor, driving one of the oldest and simplest forms of pump. The whole unit consists of only one small rotating part called a rotating joiner, or in plumber terms, a spinning nipple.
When assembling the coils on the spokes of the frame, I had no idea how many coils and at what diameter was needed to pump the water to the 16 metre head. The water wheel ended up about two metres in diameter. As the water wheel and the spiral both needed to dip into the water, the coil has to be the same diameter as the paddles.
Three quarter inch (19 mm) poly pipe can be coiled down to about 500 mm in diameter before it starts to kink. If the coils are kept close together, around 40 coils can be made. I decided to make two lots of coils consisting of 20 coils each, so there were two openings to take a gulp. In theory this should have pumped twice the volume of water as a single coil rotating at the same speed. However, this proved to be too heavy for the flow of the stream to move, so I had to remove one coil of pipe. As Jills place is three hours drive away, there was much guesswork involved in my workshop and redesigning on site.
The final coil design saw 50 metres of three quarter inch (19 mm) poly pipe coiled into 20 loops from 2 metres to half a metre diameter. The pumping rate at this site is about one litre a minute but varies from season to season.
Figuring it out
My theory then is that to successfully pump water, the coiled pipe needs to be about three times as long as the height it is being pumped to. Thats a 3:1 ratio. I assumed that the size of the pipe is less important than the total length. Larger loops are more effective at forcing water up than small loops but consume more length. Fewer larger loops may be just as effective as many smaller loops.
The water exiting the smallest coil in the centre is piped into the hollow shaft of the water wheels axle. The end of this then joins a stationary water pipe near the bank, in this case connected to a boom arm (described below). To join the rotating shaft to the fixed poly pipe, a joiner is needed that can spin constantly. Unless the connection is perfectly in line, these watertight rotating joiners can wear out quickly.
To avoid flood damage to this water wheel pump, I mounted the axle and bearings onto a three metre boom of 100 mm RHS that pivots at the end anchored to the bank. Along this boom, a height adjustable support is set into the bank. A steel cable is attached to the water wheel that is operated by a winch fixed even higher up the bank (see illustration). Not only does this allow it to be cranked out of the water if a flood is imminent and hoisted safely above flood height, but it also allows the water wheel to be lowered or raised to match the high and low flows of the river.
Here are a few more pointers to help with constructing the coil section. To attach the poly pipe to the angle iron spokes, use 1 mm stainless steel wire (you can order it from engineering suppliers). The end of the three quarter inch poly pipe that scoops up the water should be increased in diameter for the last loop. I used one inch (25 mm) for half a loop and then one and a quarter inch (32 mm) poly pipe for the last half a loop. This allows for greater volume to be scooped up each rotation.
As both water and air are pumped up the delivery line together, it is best to send the pumped water directly to the storage tank or dam. If the inlet and outlet line to the tank are the same, a special air bleed line close to the pump will be needed, as Jill discovered when trying to use the taps on the same line or have a shower!
A one-way valve will also need to be set in the line to stop water draining back out when the wheel is not pumping. A filter isnt a bad idea either. You can also fix a fly wire guard to the inlet end of the coil that also reduces debris from entering the system.
One modification that had to be made over the last couple of years has been a more robust and reinforced hollow shaft. The constant flexing and movement of the water wheel, especially with faster flows, stresses metal and any weak spots are soon discovered. The water wheel was sited on a slight bend in the river where it was narrow and the water had a higher velocity.
Variables that allow this design to pump effectively are:
This spiral pump was a direct replacement of a small standard piston pump and has proved to be just as efficient at pumping a set volume per day.
Overall, its a beautiful piece of alternative technology. And Jill says it also doubles as relaxation therapy: after a torrid session dealing with planet wreckers, sitting by the river watching it quietly turn puts some equilibrium back into the soul.
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