Newsletter and Technical Publications
<Sourcebook of Alternative Technologies for
in Small Island Developing States>
PART B - ALTERNATIVE TECHNOLOGIES
2. TECHNOLOGIES APPLICABLE TO VERY SMALL, LOW CORAL ISLANDS
2.1 Freshwater Augmentation Technologies
Although it may not be immediately obvious, pump selection is a
specialised task and there are many factors to be considered. Relevant
factors identified by UNESCO (1991) include flow rate (based on design
demand); total lift or head; source of supply (e.g., well, borehole,
stream, or reservoir); water quality; maintenance, including spare parts
availability; level of technical expertise of local personnel; and, types
and amounts of energy consumed. To meet these often highly specific
combinations of factors, many types, kinds and sizes of pumps are
available for use in water systems. On small, high islands, where
groundwater is abstracted from deep wells, motor-driven pumps are
generally used. In contrast, hydraulic ram pumps may be applicable in the
rural, inland areas of small, high islands.
Figure 24. Schematic of a suction pump (Pickford, 1991)
This section covers those pumping technologies that are most applicable
to SIDS; namely, technologies that may be used on very small, low islands
(handpumps and solar pumps), and technologies that may be used on small,
high islands (hydraulic ram pumps).
There are many classes of handpumps in general use. The type most
frequently used for potable water pumping on small islands is the
reciprocating (plunger) pump. The following variations on this pump design
are the most widely used; namely, the suction pump which is generally
installed in shallow wells; and, the lift pump or the so-called deep-well
pump. In the suction pump, the plunger and cylinder are located above the
water level, usually within the pumpstand itself (Figure 24). The suction
pump relies on atmospheric pressure to push the water upwards into the
cylinder: this type of pump does not "lift" the water up from
the source, instead the pump reduces the atmospheric pressure on the water
column in the suction pipe and the atmospheric pressure on the water
outside the suction pipe pushes the water up. In the lift pump (or deep
well pump), the cylinder and plunger must be submerged or located within
the suction lift of the water (Figure 25). Since the water level normally
changes with season throughout the year, or even daily with tidal
variations, the cylinder should be submerged at all times (Dali, 1990).
The choice of which handpump to use in a given situation will depend on
depth to water; cost; location of the well in respect to the user; amount
of use anticipated; quality of water; and, cultural requirements.
Figure 25. Schematic of a lift pump (Pickford, 1991)
The simplest solar pumping system consists of a solar module, or array
of modules, wired directly to a pump. This type of solar pumping system is
called an array-direct, solar pumping system because no batteries are
required. Whenever the sun is shining, an array-direct, solar pumping
system will operate and supply water to storage tanks. It will not operate
during rainy weather. To overcome this limitation, another solar pumping
system is the solar system with battery back-up. The primary components of
this type of solar system are a solar module or array, a charge
controller, a battery or bank of batteries, and the pump. In a system with
battery back-up, the batteries play the same role as the storage tank in
the array-direct system. Electricity is stored rather than water. This
system operates just the same as any electric pumping system except that
12 or 24 volts direct current is generally used. The pump can either be
switched on and off manually, or a pressure switch or float can be used to
provide automatic pumping whenever a faucet is opened. Solar pumping
systems in remote areas can serve a variety of residential areas,
including individual households, groups of households, or communities. The
choice of the level of service to be provided to residential areas is
mostly a function of population density. In sparsely populated areas, a
household system is the logical choice; however, as population density
increases, it becomes more appropriate to use solar-powered pumps in more
Hydraulic Ram Pumps
Hydraulic ram pumps are water pumping devices that are powered by
falling water. The pump works by using the energy of the falling water to
lift a small amount of that water to a much greater height. Although
hydraulic ram pumps come in a variety of shapes and sizes, all have the
same basic components (Figure 26). 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 (Figure 27).
As the water accelerates into the pump, the pressure rises until it is
higher than that in the air vessel, when 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 down and the
pressure in the pump body recoils or drops below the delivery pressure.
The delivery valve then closes, stopping any backflow from the air vessel
into the pump and drive pipe. Throughout the cycle the pressure in the air
vessel steadily forces water up the delivery pipe. The air vessel smooths
the pulsing inflow through the delivery valve into an even outflow up the
delivery pipe. The pumping cycle happens very quickly, typically 40 to 120
times/minute. While each pumping cycle delivers only a very small amount
of water, over 24 hours, a significant amount of water can be lifted
(Jeffery et al., 1992).
Figure 26. Diagram of a typical ram assembly (Dali, 1990)
Figure 27a. Acceleration
When the impulse valve is
open, wateraccelerates down the drive pipe and discharges through the open
The friction of the water flowing past the moving parts of the
valve cause 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
Figure 27b. Delivery
As the impulse valve slams
shgut, 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.
Figure 27c. Recoil
The remaining flow in the drive
pipe recoils against the closed deliverey valve - rather like a ball
This causes the pressure in the body of the pump to
drop low enough for the impulse valve to reopen. The recoil
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 open impulse
starting the cycle again.
Extent of Use
Handpumps are used on a large number of the very small islands
throughout SIDS. A recent study on the use of handpumps in the Pacific
region (Mourits and Depledge, 1995) showed that locally-produced, shallow
well handpumps can be found in Papua New Guinea, Solomon Islands and
Kiribati. Their low cost and simple design makes them an appropriate
technology and fairly successful. Popular shallow-well handpumps are the
Southern Cross KDC from Australia and the NIRA AF85 from Finland. These
pumps have a higher cost and are usually supplied through aid-funded
projects with government support. Deep-well pumps are not common, as most
of the population in the Pacific region live in the coastal areas where
groundwater is relatively shallow.
The technology of solar pumping systems has improved, and the cost has
been reduced considerably in recent years. Hence, use of solar-powered
pumping systems is therefore becoming more common, with examples of
solar-powered pumping systems for village water supplies being found on
some islands in the Torres Straits, between Australia and New Guinea, and
on Chuuk, Federated States of Micronesia. In French Polynesia,
solar-powered pumping systems have been installed on six atolls and three
high islands, although on the high islands, the solar-powered systems were
later replaced by electrified pumping systems. On Kiribati, solar-powered
pumps were installed in places where the distance from the village to the
well and galleries exceeded 750 m.
Hydraulic ram pumps are used on some high islands, such as the Solomon
Islands and Vanuatu.
Operation and Maintenance
Handpumps are generally operated with some type of lever system and are
designed in such a way that even children can draw water. Maintenance
requirements are limited and can generally be performed by the user with
minimal training. However, it is important that spare parts are readily
available or the pump can rapidly become useless. Solar pumps require
little operation or maintenance, especially for the array-direct, solar
systems. Maintenance mainly consists of keeping the equipment in order
(especially the batteries) and ensuring that the array is clean and not
shaded by trees or other objects. Once an hydraulic ram pump has been
started, it will operate automatically and continuously. Maintenance
consists of inspection of all the threaded and flanged joints to check for
leaks; removal of the air vessel to check the delivery valve rubber for
signs of wear or damage; and, annually dismantling the pump to completely
and thoroughly clean the inside.
Level of Involvement
The installation and maintenance of handpumps can be undertaken at
village level. Women should be trained in this task as they tend to use
the pumps the most. Solar pumps similarly do not require an high-level of
training to install, operate and maintain, while, with some training,
hydraulic ram pumps can be operated and maintained at village-level.
Prices of handpumps vary considerably. For example, in 1995, a
plastic-bodied pump from E & B Marine, Edison, New Jersey, sold for
around $55, while a diaphragm pump like the Southern Cross KDC sold for
approximately $120 to $160, and a direct-action pump such as the NIRA
AF-85 sold for about $450 to $465.
Commercially-available solar pumping systems range from relatively small
ones, pumping about 10 m3/d over a 3 m head, to medium-sized
systems pumping about 100 m3/d over an 80 m head. During the
past decade, the cost of solar-powered pumps has approximately halved due
to technological improvements in the photovoltaic cells and increased
sales. Indicative prices in 1995 ranged from $2 100 for the Photocomm
Submersible Pump 9300 system, which delivers up to 0.13 l/s from well
depths of 75 m, to $13 000 for an A.Y. Macdonald 211012 DK submersible
pump, which delivers up to 0.35 l/d from well depths of 40 m.
One of the greatest benefits of the hydraulic ram pumping systems is
that they have extremely low running costs. The purchase cost of a pump is
usually only a fraction of the total system costs; the pump drive and
delivery piping are usually the most expensive capital components. Prices
of hydraulic ram pumps vary enormously, with the cost increasing
significantly if the pump is imported due to the added costs of shipping
and customs duty. An hydraulic ram pump of traditional design,
manufactured in Europe or North America and imported to a developing
country, might cost between $1 500 and $4 000, while the same pump
manufactured locally in a developing country, using available materials,
is likely to cost only 20% of this amount.
Effectiveness of the Technology
Handpumps are an effective method for abstracting water from a well.
Overpumping of a well using a handpump would be most difficult. In
addition, hand-pumped wells are normally less subject to surface pollution
than bailed wells.
The array-direct solar pumping system provides 24 hour per day water
because water is always available from the storage tank provided the
demand does not exceed the tank capacity. A battery system provides 24
hour per day water because the pump can always be operated by means of
electricity stored in the batteries.
Test results of commercially-manufactured hydraulic ram pumps indicate
that an overall efficiency of 65% can be obtained, provided that the
design, manufacturing, and tuning of the ram installation are optimal.
Most hydraulic rams will work efficiently if the supply head is about 30%
of the delivery head. Standard hydraulic ram pumps are available in the
range of 5 to 400 l/m, with maximum delivery heads of about 125 m.
In SIDS, handpumps are most suitable for the abstraction of water from
shallow wells on small, low-lying islands, as well as in the coastal areas
of the small, high islands. Wells fitted with handpumps should be raised
and fully covered for protection from surface pollution.
Solar powered systems are suitable for islands where there is sufficient
solar energy available and either battery back-up or other energy sources
are provided to ensure near-continuous pumping, and/or sufficient water
storage is provided to cater for periods of no sunshine. Solar-powered
systems also requires sufficient clear space to prevent shading of the
solar panels by other objects.
Hydraulic ram pumps are only suitable for use on high, small islands
with rapidly dropping water courses that do not run dry during extended
periods with no rainfall.
Handpumps have few operational costs and generally low maintenance
costs. There is minimal risk of overpumping a well using an handpump. Use
of the pump helps to protect against surface pollution. Handpumps can be
maintained by villagers with minimal training.
Solar pumps have no recurring fuel costs, and require little or no
maintenance. The systems have few operational requirements, and are silent
and pollution-free when in operation.
Hydraulic ram pumps make use of a renewable energy source that helps to
ensure low running costs. Because they pump only a small proportion of the
available flow, they also have few environmental impacts. This simplicity
and reliability result in a low-maintenance requirement. Hydraulic ram
pumps have good potential to be locally manufactured. Operation is
automatic and continuous, requiring little supervision or human input.
Handpumps require a readily available supply of spare parts. In
contrast, solar pumps have an high initial cost. Problems of maintaining
batteries still occur, particularly in the tropics (although this problem
is specific to those solar system with battery back-ups). Hydraulic ram
pumps are limited to use in hilly areas with year-round water sources.
They can only pump a small fraction of the available flow, and, therefore
,require source flows much larger than actual water flow delivered to the
users. Hydraulic ram pumps can have an high capital cost in comparison to
some other technologies, and are typically limited to small-scale
applications. Hydraulic ram pumps may require some special skills for
design and installation.
No cultural inhibitions have been identified with respect to handpumps
and hydraulic ram pumps. However, because solar arrays must be exposed to
direct sunlight for them to generate electricity, trees can pose a problem
in some location, as trees often are a valuable source of food and
building materials and cannot be cut down indiscriminately to reduce
Further Development of the Technology
Handpumps are always being improved by developing simpler pumps and
using different types of materials to construct them. Likewise,
solar-powered pumping can be further improved by improving the design of
the solar (or photovoltaic) cells, to provide more a efficient electrical
supply. Designs should be developed which are more suitable to local
conditions in SIDS. In the case of hydraulic ram pumps, this would
specifically involve designing hydraulic ram pumps that could be
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