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Report 5 of 5: Ramming It
- Nepal
Introduction
The automatic hydraulic ram is a pumping device for lifting water to heights of over 100 metres. It is powered by falling water and has been widely used for over two centuries in many parts of the world. The pump works by using the energy of a large amount of water falling a small height to lift a small amount of that water to a much greater height. In this way, water from a spring or stream in a valley can be pumped to a village or irrigation scheme on the hillside. Wherever a fall of water can be obtained, the ram pump can be used as a relatively cheap, simple and reliable means of raising water to considerable heights.
It is an ideal machine for water pumping if certain conditions are satisfied because it works solely on the power from falling water carried in a pipe from a spring, stream or river without any need for an additional power source. However, it cannot be used everywhere. For example, it cannot be used to pump still water from a well, pond or lake unless there is a separate, flowing water source nearby.
For the people living higher up in the Himalayas, access to water is limited and women spend hours walking to collect enough water for their daily needs. In Nepal, in the village of Galang, the introduction of a ram pump over a decade ago has changed the lives of the local community. All that is necessary for a ram pump to work is falling water and once it has been installed, it costs relatively little to operate.
In Galang, the ram pump provides one hundred families with water for their daily requirements. Each villager pays 10 rupees per month (US$0.50) to the manager and maintainer of the ram pump to ensure that the pump and pipes are kept in good working order. For any similar scheme to be successful, it is essential for someone to take on the role of calling meetings to discuss management and any particular problems, and carry out the maintenance work.
Use of ram pumps
Ram pumps can only be used in situations where falling water is available which restricts them to three main applications:
- Lifting drinking water from springs in valleys to settlements on higher ground
- Pumping drinking water from clean streams that have a significant slope
- Lifting irrigation water from streams or raised irrigation channels
Ram pump operation
Although ram pumps come in a variety of shapes and sizes they all have the same basic components. The flow of water at the source needs to be measured to establish if it is enough to operate the ram. Naturally occurring sources of water tend to dry up during the year and this needs to be considered.
Ram pumps have a cyclic pumping action that produces their characteristic beat during operation. The cycle can be divided into three phases: acceleration, delivery and recoil.
Acceleration
Normally, the impulse valve remains open due to gravity so, when the supply is connected, water accelerates down the drive pipe and starts to escape past the open valve. As the water passes around the valve, it tends to drag it closed and, when this drag reaches a critical level, the valve starts closing. Once the valve has begun to move, it closes very quickly.
Delivery
As the impulse valves slams shut, the escape of water is stopped. However, the water already flowing in the pipe has considerable momentum which must be dissipated. For a fraction of a second, the water in the body of the pump is subjected to a large and sudden surge in pressure. This pressure rise, known as "Water Hammer", forces water to surge through the delivery valve which is held open by the flowing water. The surge takes the water up the delivery pipe and high into the air vessel until the pressure in the main pump body falls off. The water in the delivery pipe then tries to flow back, closing the delivery valve.
Recoil
The remaining flow in the pipe recoils against the closed delivery valve – rather like a ball bouncing back. This causes the pressure in the body of the pump to drop low enough for the impulse valve to reopen. The recoil also sucks a small amount of air in through the snifter valve. The air sits under the delivery valve until the next cycle when it is pumped with the delivery water into the air vessel. This ensures that the air vessel stays full of air. When the recoil energy is finished, water begins to accelerate down the drive pipe and out through the impulse valve, starting the cycle again.
Throughout the cycle the pressure in the air vessel steadily forces water up the delivery pipe. The air vessel smooths the pulsing in flow through the delivery valve into an even outflow up the delivery pipe. The pumping cycle happens very quickly, typically 40 to 120 times per minute. The ram is tuned to pump the greatest amount of water possible and this is normally when the ram cycle is repeated or beats about 75 times each minute. During each pumping cycle only a very small amount of water is pumped. However with cycle after cycle continuing over 24 hours, a significant amount of water can be lifted.
While the ram pump is operating, the water flowing out of the impulse valve splashes onto the floor of the pump house and is considered ‘waste’ water but it is in fact collected and returned to the stream. Although waste water is not delivered by the ram pump, it is the energy of this water that pumps the water which is delivered.
Advantages of Ram Pumps
Despite the fact that it wastes a lot of water, in places where a ram pump can be used, it has many advantages over other pumps powered by hand, animal, wind or motors.
- It does not need an additional power source and there are no running costs.
- It has only two moving parts and these are very simple and cheap to maintain.
- It works efficiently over a wide range of flows provided it is tuned in correctly.
- It can be made using simple workshop equipment.
For further information, please contact:
Intermediate Technology would like to thank the Development Technology Unit at the University of Warwick, in particular T.D.Jeffery, T.H.Thomas, A.V.Smith, P.B.Glover and P.D.Fountain, for providing the original material and diagrams on hydraulic ram pumps.
This document is an output from a project funded by the UK Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of the DFID.
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