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Links to Ram Pumps
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THE MOTORLESS WATER PUMP
| The Gravi-Chek pumps have been tested by the Center for
Irrigation Technology at the California Agricultural Technology Institute.
There are three models available, providing water at rates from 20 to 16,000
gallons per day, depending on the installation. |
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Easy to use:
 | Lightweight (35 lbs. or less), easy to carry and install in remote
areas. |
| Quick start up, no energy costs. |
| Little or no maintenance. |
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Efficient and powerful:
| Running water supplies pumping energy. |
| Durable, only two moving parts. |
| Made from tempered marine aluminum |
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| Water flows through the drive pipe into the pump and out
through the waste gate. The buoyant ball will be pulled down by the flow
of water and block the waste gate. |
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| Here the ball has blocked the waste gate. The incoming
water forces the spring loaded check valve open, allowing water to fill
the surge tank, compressing the air in the tank. |
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| When the pressure in the surge tank equals the pressure
in the drive pipe, the water from the drive pipe can no longer flow into
the pump, a “bounce-back” effect happens. The check valve shuts and the
compressed air in the surge tank forces water in the tank up to where it
is needed. The bounce back causes the water to briefly flow back up the
drive pipe, unseating the ball valve and letting the cycle begin again. |
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The Gravi-Chek pump is the
newest technology available in the ram pump industry (patent # 4,911,613). This
pump is designed to supply water up-hill without a motor: the force of water
flowing down into the pump provides all the energy needed.
Ram pumps
Ram pumps can only be used in situations where falling water is available,
which restricts them to use in three main applications:
| lifting drinking water from springs in valleys to settlements on higher
ground. |
| pumping drinking water from clean streams that have significant slope.
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| lifting irrigation water from streams or raised irrigation channels. |
Water ram
Ram pumps are water pumping devices that are powered by falling water. 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. Where ever a fall of water can be obtained,
the ram pump can be used as a comparatively cheap, simple and reliable means of
raising water to considerable heights.
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
When the impulse valve is open, water accelerates down the drive pipe and
discharges through the open valve. The friction of the water flowing past the
moving parts of the valve causes a force on the valve acting to close it. As the
flow increases it reaches a speed where the drag force is sufficient to start
closing the valve. Once it has begun to move, the valve closes very quickly.
Delivery
As the impulse valve slams shut, it stops the flow of water through it. The
water that has been flowing in the drive pipe has considerable momentum which
has to be dissipated. For a fraction of a second, the water in the body of pump
is compressed causing a large surge in pressure. This type of pressure rise is
known as water hammer. As the pressure rises higher than that in the air vessel,
it forces water through the delivery valve (a non-return valve). The delivery
valve stays open until the water in the drive pipe has almost completely slowed
downand the pressure in the pump body drops below the delivery pressure. The
delivery valve thencloses, stopping any backflow from the air vessel into the
pump and drive pipe.
Recoil
The remaining flow in the drive 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 outthrough the open impulse valve, starting the cycle again.
Efficiency and Power
The power required to raise water is proportional to the water's flow rate
multiplied by the height through which it is lifted (in a ram pump q x h).
Similarly, the power available from falling water is proportional to its flow
rate multiplied by the distance dropped (Q x H). A rampump works by transferring
the power of a falling drive flow to a rising delivery flow.
By definition Efficiency= output power/input power= qh/QH.
Efficiency is always less than 1. It is useful to know the efficiency because we
can use it to predict the delivery flow of a system and to compare two different
pumps. Rearranging the equation above gives the formula:
Delivery flow (q)= QHn/h
To obtain a good delivery flow, the efficiency of the pump should be high, there
should be a large drive flow, and the delivery head should not be too many times
the drive head. The value of system efficiency to put into the formula depends
upon many factors including the design of the pump and the system being used.
Suitable Areas
Although all watercourses slope downwards to some degree, the gradient of
many is so shallow that many kilometres of feed pipe or canal would be needed to
obtain a fall of water large enough to power a ram pump. Ram pumps can be made
to run with drive heads of less than one metre but they are not normally
considered viable unless heads of two metres or more are available. If it would
take a long length of feed pipe or canal to achieve this head, a ram pumpsystem
would be prohibitively expensive. the best geographical area for ram pumps is
one which is hilly, with rapidly dropping watercoutses and, ideally, springs.
In some areas of the world good regional records of rainfall and flow from
springs and in watercourses are kept in government offices and libraries. In
others, another agency may have carried out recent relevant studies. If any
hydrological studies are available for the region in which you plan to install
ram pump systems, you can save time, effort and costly mistakes by consulting
the records and using their findings in your site design.
After potential sites have been identified, they must be surveyed. The survey
yields information about sit dimensions and the materials required to construct
the site as well as, when more than one site is surveyed, yielding a cost and
performance comparison.
Designing a good drive and pump layout is crucial to achieving good system
performance and limiting the amount of maintenance required. The aim is to be
able to achieve a large head of water between the drive tank and pump, while
using a short drive pipe to connect them. The best and cheapest sites are thos
where the land falls rapidly, allowing all pipework to be short.
Life and Reliability
Imported ram pumps operated at fairly low throughput have proved extremely
reliable in some developing countries. Some have run without stopping for ten
years or more in systems supplied with clean water from a reservoir. this
outstanding reliability has had a curious sideeffect - when such pumps finally
stop the beneficiaries have no recall of their source, no knowledge of how to
maintain them and no access to spare parts. Failures in ram pumpsystems often
occur outside the pump itself - blockage of dilter screens, damage to pipes,
sedimentation of pipes and tanks etc. Poorly located drive pipes sometimes show
perforationdue to a process called cavitation.
Pumps made in local workshops are less durable than some of the imported
machines made of cast iron, but their lower price usually makes them better
value than either imported ram pumps or other pumps of comparable throughput.
They also have the advantage of being locally repairable with ready access to
spare parts.
Ram pumps run unattended for long periods, so running faults can go unattended
for days or weeks. This can lead to expensive failures. For example, blockage of
the output for long periods can cause fatigue failure of components (unless a
costly pressure relief valve is fitted). The historical high reliability of ram
pumps may reflect in part the social circumstances of their traditional use on
large farms or mission stations where regular checks are made. The routine
supervision of village systems may be much poorer and great care should be taken
to ensure adequate caretaking.
Tuning to Suit Site Conditions
Any particular ram pump is normally capable of running under quite a wide
range of conditions. Most manufacturers quote operating ranges of drive head
(H), drive flow(Q) anddelivery head (h) for each pump size and give some
indication at a particular site. In situationswhere the water source has a
larger flow than that required, each pump can be tuned to use as much drive
water as possible to ensure minimun capital costs. When there is a limited
amount of drive water available, the impulse valve has to be tuned to make the
most efficient use of that water to produce the best possible output. At many
sites there is a seasonal variation in the drive flow available and this is
accommodated by varying the pump tuning or varying the number of pumps in use.
Economic Factors
One of the greatest benefits of ram pump systems is that they have extremely
low running costs. There is no input of expensive petroleum fuels or
electricity, making the systems very inexpensive to operate. The purchase cost
of a pump, however, is usually only a fraction ofthe capital cost of a system:
drive and delivery pipework are usually the most expensive parts. Ram pump
systems can be subject to economies of scale. For example, where there is enough
drive flow, having several pumps at one site gives a lower unit cost then if the
same pumps were installed at separate sites. In situations of plentiful drive
flow, buying one large pump may be cheaper than buying several smaller ones,
although this option does have disadvantages: having a single large pump
involves a loss of system flexibility across a range of flows and if the pump
needs maintenance or fails, 100% of the delivery is lost. With several smaller
pumps, a pump can fail or be stopped for maintenance without stopping the entire
delivery flow.
Prices of ram pumps available today vary enormously. If a pump is imported the
costs of shipping and customs duty may significantly increase the acutual cost
of the pump to its users.
Social Factors
The significance of social factors to any development project cannot be over-emphasised.
This is particularly true of community water supplies, which involve every
member of the community on daily basis. A large amount of written material is
available highlighting theimportance of community involvement and detailing
examples of participation in project initiation, design, management, and
finance. It is strongly recommended that anyone exploring the possibility of
initiating a community water supply should obtain some of the available
literature and give great attention to the social aspects of the project. Good
engineering is only one part of sustainable, economic and equitable water supply
system. Without complete community involvement, even a water supply system that
is technically perfect is likely to encounter serious problems and may fail
altogether.
Adequate community involvement is particularly important during the period of
system appraisal and design, and is dependent on good communication. When
sufficient time and care is invested in producing a widely acceptable design,
ram pump technology can be very appropriate to rural areas and be capable of
true village-level operation and maintenance.
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