Author: Rod Hughes, Leafcutter Permaculture
The hydraulic ram pump is a beautiful piece of alternative technology which can – in the right conditions – shift water from one point on a site to a higher elevation without the input of energy beyond the kinetic energy of the water itself. Amazing!
The ram pump was reportedly invented about 200 years ago and while there are many variations in design detail they all rely on the same general operating principles.
The ram pumps works by taking in water at one “hydraulic head” (pressure) and flow rate, and outputting water at a higher hydraulic head and lower flow rate.
Figure 1: Schematic of hydraulic ram pump operation (Source http://www.rampumps.net)
If you look at the diagram above, you see water enters through the delivery pipe (left hand side of the graphic) and its kinetic energy and friction are enough to close the waste valve (on the right hand side).
The sudden closing of the waste valve initiates a water hammer effect causing the pressurised water to open the check valve (centre of image), allowing water into the air chamber.
The pressure in the air chamber causes this small amount of water to exit the pump into the delivery pipe on its way to the delivery destination, normally an elevated header tank.
With the back pressure of the delivery pipe, the check valve then closes and the cycle begins again with inflow water re-pressurising against the waste valve. This process repeats anywhere from 25 to 300 times per minute.
It’s important to know that as much as 90 per cent of the water entering the pump exits via the waste valve before it closes, so the pump needs to be positioned or configured so that the waste water can return to the reservoir or stream.
Ram pumps need a continuous flow of water to operate. They also need a minimum of head from the source. There seems to be quite a range of opinion on this point - about what is the minimum head required, with one source suggesting that one foot (~ 0.3 m) of head in the water source would be sufficient to operate a ram pump. Others suggest a minimum of one metre.
There is also a ratio that determines the results of the pump and while there is wide variation in opinion on what lift can be achieved, notionally the amount of lift possible will be seven times the delivery head. That means that if you have a fall of 1 m from your water source to the ram pump, you should be able to deliver water to a point 7 m higher up in the landscape.
Figure 2: The diagram above shows some of the key elements of ram pump installation (Source: http://www.rampumps.net)
How you build and place the drive pipe is critical because this determines the magnitude of the “water hammer” during the operating cycle. This water hammer determines the maximum pressure that can be reached by the pump, and the amount of water that can be pumped.
Rigid steel pipe gives the greatest water hammer effect, which provides the most efficient operation of the pump and so is recommended for the drive pipe wherever possible. The drive pipe should be laid as straight as possible with gentle curves only used if they can’t be avoided.
A disclosure: I built the ram pump shown in the photo above. It’s just going to take a bit of fine tuning and overcoming some installation challenges to get it to work. All an experiment!
The use of high-pressure hard plastic pipe may be possible, but with significantly reduced performance. In some cases such plastic (PVC) pipe may be preferable if you can live with reduced performance. For example, PVC pipe may be easier to install, and may avoid problems arising from corrosive water. Normal agricultural poly piping should not be used for the drive pipe as it will reduce performance and is likely to burst from the water hammer after a period of operation.
Where you don’t have enough fall, you can increase the chances that the pump will operate. As shown in the diagram below, a supply pipe is run from the supply source to a stand pipe which can be made of PVC or steel. The stand pipe should be open at the top (but screened to keep out debris). The drive pipe runs from the stand pipe to the pump inlet as normal. The key considerations are that the supply pipe must be at least twice the diameter of the drive pipe and that the top of the stand pipe must be several centimetres above the level of the water supply.
Figure 3: Scheme to increase inlet “head” using stand pipe (Source: http://www.rampumps.net)
A further useful modification is the addition of a “snifting” valve between the check valve and the air chamber. This is because over time, the air in the chamber will dissolve into the water, reducing its effect. The snifting valve will introduce a small bubble of air into the chamber with each cycle. The use of a partially inflated small tyre tube (eg bicycle) with its valve closed can also be inserted into the pressure chamber during construction. This helps cushion the impacts of the hammer effect on the pump, which can be considerable.
The ram pump is often useful in remote locations since it needs no outside source of power. Small versions can be built with simple and readily available materials and with no technical expertise required. Larger and more robust variations, for example, to supply a village in a developing country, can still be built with relatively low level engineering capacity. In general, the ram pump has very few moving parts and so is cheap to maintain and should work as long as water is available, therefore providing a very useful consideration in a permaculture design project.
Photo: Industrial-sized ramp pumps can be set up to deliver water supply at the village scale