· Mechanical pumps will often be needed. Seek expert local advice on what is suitable and remember there will be future need of operators, fuel and spares.
· Pumping requirements should always be calculated to be minimal. Maximum use of gravity flow for treatment processes, water conveyance and distribution should also be pursued.
· As it is always difficult to predict for how long a refugee water supply will be required, emergency water supply solutions involving pumping devices should guarantee a long-term and effective system from the beginning. Ad-hoc approaches to solving emergencies are bound to be problematic and difficult to operate and maintain, unless solutions are chosen in accordance with the realities of the site, the long-term operation and maintenance possibilities available and sound engineering practice.
1. Once an adequate source of water has been established, arrangements are necessary to store and distribute the water to meet minimum needs on a continuing and equitable basis. The water source may be situated topographically higher than the refugee camp or the points where water distribution should take place; all efforts should then be made to study the possibility of conveying the water by gravity flow; operation and maintenance requirements of gravity fed systems are minimal and negligible if compared to the high cost and technical requirements of pumping systems.
2. In areas subject to seasonal flooding, or where the level of a river source varies markedly, great care must be taken in the siting of any pumps, distribution, storage and treatment systems. It may even be necessary to mount a pump on a raft.
3. Water can be raised in two basic ways: by hand, using some kind of water container or bucket, or by using pumps. A captive rope and bucket carries a low pollution risk and is more reliable and much cheaper than any pump. Where this system can meet the demand, it is to be preferred (not more than 200 people should depend on a well with one rope and bucket!). The importance of teaching refugees to use one single bucket does not need explanation. Nobody should be allowed to put individual containers into the source (See 5.29)
4. The main uses of pumping equipment in refugee water supply systems are:
i) Pumping water from wells or boreholes;
ii) Pumping water from surface water intakes;
iii) Pumping water into storage reservoirs.
Additionally, in some cases where gravity flow may not be used for other requirements, there may be a need to use pumping equipment for other purposes (feeding water treatment plants, boosting the flow through long pipelines, feeding water tankers, etc.); refugee water supply systems should use gravity flow as much as possible for these purposes as a way to minimize long-term requirements.
5. Based on their mechanical characteristics, pumps may be classified as:
i) Reciprocating Pumps: These pumps have a plunger (piston) which moves up and down within a cylinder to produce positive displacement of water. On the upward stroke the plunger forces water out through an outlet valve, and at the same time water is drawn into the cylinder through an inlet valve; the downward stroke brings the plunger back to its starting position, and a new operating cycle can begin. They can be operated by hand, wind or engine power; their efficiency is low (25-60%); their capacity range is between 10 and 50 litres per minute; their valves and pump seals (washers) require regular maintenance attention. Several types of reciprocating pumps may be distinguished:
Fig. 13 Suction Pump
a) Suction pumps: In this type the plunger and the cylinder are located above the water level, usually within the pump itself. (fig 13). Contrary to popular belief, this pump does not lift the water up from the source, but relies on atmospheric pressure to push the water upwards; this limits the effectiveness of these pumps to pumping from sources that are not more than 7 metres lower than the suction valve and depends on the altitude of the site where pumping is to take place.
b) Deep well (lift) pumps: In these pumps, plunger and cylinder sets are located below the water level. Water may be lifted with these pumps up to 180 metres (or even more). Forces created by pumping work increase with depth and maintenance requirements become more frequent and difficult.
Fig. 14 "Deep Well" (Lift) Pump
c) Free delivery (force) pumps: These pumps are able to pump water from a source and to deliver it to a higher elevation or against pressure. They may be used in deep or in shallow wells. They operate in accordance with the same principle described for reciprocating plunger pumps, with the difference that, for force pumps, plungers are located at the top and, therefore can be used to force water to elevations higher than the pump site. These pumps are frequently provided with an air chamber to even out flows in such a way that a continuous stream comes out of the pump outlet at all times during pumping. For deep wells the cylinder is put down in the well to allow the lifting of water even from depths greater than 7 metres.
Fig. 15 Free Delivery (Force) Pumps
d) Diaphragm pumps: Their main component is a diaphragm, a flexible disc normally made of rubber or metal. Non-return valves are fitted into the inlet and outlet (Fig 16). The edge of the diaphragm is bolted to the rim of the water chamber but the centre is flexible. A rod, fastened to the centre, moves it up and down. As the diaphragm is lifted, water is drawn in through the inlet valve; when it is pushed down, water is forced out through the outlet valve. Pumping speed usually is about 50-70 strokes per minute. Many new handpump designs are based on this principle.
Fig. 16 Diaphragm Pumps
ii) Positive Displacement (Rotary) Pumps: These pumps lift water when their mechanisms rotate; due to that rotation, water is "picked" and forced up. The most widely known positive displacement pumps are the helical rotor pumps, whose pumping mechanism consists of a single thread helical rotor rotating inside a double thread helical sleeve. The two closely adjusted helical surfaces force the water up, in a uniform flow manner and at a rate proportional to the rotating speed. Due to their design, these pumps require no valves; their maintenance requirements are minimal, but maintenance action is, however, relatively complex and requires skills (training) and equipment. They may be used to pump from as deep as 150 metres or more; they are very well suited for low output-high lift pumping and may be efficiently operated with hand, wind or motor power.
Fig. 17 Helical Rotor Pumps
iii) Axial Flow Pumps: In this type of pump, radial blades are mounted in an impeller (propeller type of wheel) which rotates in an enclosure (casing). The pump's action is to mechanically lift water when the impeller is rotating; water moves parallel to its axis. The casing has fixed guide blades that dissipate the whirling movement of water before it leaves the pump. These pumps have a depth range varying between 5 to 10 metres; their flow capacity is high. Due to their construction characteristics, these pumps can handle waters which have a fair amount of sand or silt in suspension.
Fig. 18 Axial Pump
iv) Centrifugal Pumps: These pumps are also made with an impeller within a casing. In these pumps, the impeller is a wheel with blades radiating from the centre to the periphery which, when rotated at high speed, impart movement to the water and produce an outward flow due to centrifugal forces; the angle between the direction of entry and exit of water flow is 90 degrees. The casing is shaped in such a way that part of the energy created by the water's movement is converted into useful pressure to force water into the delivery pipe; water leaving the impeller creates a suction which will force additional water from the source into the casing under static head. Impellers and casings can be installed in series to increase water pressure; each set of impeller and casing is then called a stage; when this is done, all impellers are attached to a common shaft and therefore rotate at the same speed, water passes through each stage and gains additional pressure. Multiple stage centrifugal pumps are normally used for high pumping heads. The performance of a centrifugal pump depends largely on its rotational speed, its efficiency improves as the speed increases; high speeds, on the other hand, lead to more frequent maintenance requirements. The usual depth range of single stage pumps varies between 20 and 35 metres; multi-stage shaft driven pumps are normally used for depths between 25 and 50 metres. If the centrifugal pump is directly connected to an electric motor in a common housing as a single unit for operating below the water level, the set is called a submersible pump. These sets are usually supported by the discharge pipe which conveys the pumped water to the surface. Submersible pumps are extremely sensitive to the presence of sand particles in the water; the abrasive action of sand shortens drastically the life of the pump. Submersible pumps are usually a "tight fit" in a tube well as their outside diameter is usually 1 or 2 cm. less than the internal diameter of the casing; consequently, care should be taken to place these pumps only in wells which have been checked for alignment, as any small bend in the bore or its casing may obstruct the passage of the pump into the well.
Fig. 19 Centrifugal Pump
Fig. 20 Three-Stage, Shaft Driven Pump
Fig. 21 Submersible Pump
v) Hydraulic Rams: Basically, rams may be defined as hydraulically driven pumps; they require no fuel or electricity to operate. They operate by making use of the gravitational energy contained in a large amount of falling water to pump a small amount up a high distance (Fig 22). Rams require a steady and reliable source of water whose yield should be larger than the total pumping requirements. The amount of water and the height it may reach depend on the height and output of the source. They are very suitable in hilly or mountainous areas but may not be used to pump water from wells. A large amount of water flowing down from the source through a drive pipe into the ram's chamber compresses the air inside which later expands and drives a small amount of water up the delivery pipe. A ram can rarely pump more than 25% of the source's flow to higher elevations; the higher the water must be pumped the smaller the flow will be. The advantages of hydraulic rams are that they have no running costs related to energy supply, they are simple machines that any skilled plumber should be able to construct; simple equipment and materials, usually available even in quite remote areas, may be used to make them; they only have two moving parts which require maintenance attention. Maintenance is simple and infrequent, it includes a periodical replacement of valve washers, tightening bolts and tuning (adjustment of the non-return valve). If a hydraulic ram is to be used to pump water from a stream, it will be necessary to build a storage tank to ensure a regular, constant flow into the drive pipe; if the water is likely to have a lot of suspended particles (sediment) a sedimentation tank will be necessary (See 8.14; 6.16), as rams are extremely sensitive to sand or silt particles. Drive pipes must be made of galvanized iron, they should be as straight as possible and should be well anchored, to avoid movement. Accurate planimetric and altimetric surveying of the ram site and its installations is recommended before final development plans are made. In cases when the required pumping capacity is greater than the one a single ram may provide, a battery of several rams may be used, all of them connected to a single delivery pipe (the water source should, of course, be of adequate capacity); it is also possible to use the "waste water" from a ram to operate a lower ram or to incorporate a ram into a "break pressure tank" (See 10.8). These possibilities are shown in Figure 22.
Fig. 22 Hydraulic Ram Installations
6. A variety of possibilities are available for choosing the source of power required for pumping. They range from the most traditional ones (hand power, animal traction) to technologically more complicated ones (wind power, fuel-driven engines, solar energy). Suitability, relevance, availability and effectiveness in the real working conditions are the factors to be taken into account when deciding on the type of power supply required for pumping.
7. In many developing countries draught animals are still widely used; they are a common and vital source of power. Camels, donkeys or oxen are used to lift irrigation water from large diameter wells which do not normally meet potability standards (See 3.5). For human water supply, the best way to use animal power is by covering the well with a properly constructed sanitary apron through which the pump is installed with a water tight connection; the apron should have an impermeable drainage canal to lead drainage away from the well mouth (at least 35 metres). The rotating power generated by the animals pulling a treadmill mechanism is transmitted to the pump through a gear box (Fig. 23). To be effective, this requires slow moving, large displacement pumps.
Fig. 23 Mechanism for Animal Traction Pumping
8. The technology involved in the construction of efficient and appropriate windmills has advanced in recent years. The feasibility of using windmills as a source of wind power for human water supply depends, however on a large variety of factors; the system may only be reliable if there is a guarantee that all these factors will be fulfilled to maintain a constant supply. Winds are required to have a velocity of at least 2.3 metres per second during 60% of the time. The water source's yield should be at least equal to the pump's output. Enough storage (at least 3 days demand!) should be possible in order to cushion times of low wind or calm weather. Additional information on the design of the windmill, technical specifications and operational requirements should be sought, assessed and compared to the possibilities of site and source before deciding on its use. Photovoltaic cells are literally capable of converting solar energy into electricity. The use of photovoltaic cells has rapidly evolved during the past thirty-five years and is now a proven power source for many applications, including water pumping. Feasibility of solar power pumping should always be explored, especially in remote places where it is difficult, or impossible, to guarantee a timely supply of fuel. There is a cost-effective role for sun-powered pumping in many refugee water supply applications. For moderate size demands (1500 to 2500 persons at 20 litres per capita per day), it could be implemented at costs comparable to hand pump based systems; operation and maintenance activities are minimized by the need to cater for only one pumping set and by the minimal requirements of such sets. For relatively shallow pumping, submersible centrifugal pumps are more commonly used with solar power, whilst for deeper pumping requirements, reciprocating pumps may be more cost-effective. A typical sun-powered pumping system has an array of photovoltaic cells to convert light to electricity, a set of batteries to store the energy, and the electric pump and other components to control, conduct, condition, protect, support and back up the system (the control panel). The design of such a system should be entrusted to specialists and should be based on detailed specifications of output requirements, on the expectation for future growth in demand or system expansion and on other details pertaining to the site and its climatic conditions. All designs should also contain a "users manual" covering basic operation, maintenance and safety requirements, and other instructions on service and repair.
Fig. 24a Windmill Installations (groundwater)
Fig. 24b Windmill Installations (surface water)
Fig. 25 Solar Powered Pumping System
9. Due to their comparatively lower running costs, Diesel engines are the most widely used fuel driven engines in water supply systems. They are cost- effective power sources for medium and large pumping installations; for these type of installations fuel consumption would vary between 0.15 and 0.25 litres per hour per Horsepower. They can operate independently in remote areas; they only need a continuous supply of fuel and lubricants. A Diesel engine operates through the compression of air to a high pressure in its combustion chamber, this compression raises the air temperature to over 1000 degrees Celsius; when the fuel is injected through nozzles, the compressed mixture of air and fuel ignites spontaneously. Diesel engines may drive any type of pump; gearing or any other type of suitable transmission connects the engine to the pump. It is generally recommended that engines should be selected to provide some 25% surplus power, to allow for future heavier duty.
10. These type of motors should be preferred as a source of power for pumping if a reliable supply of electricity is available, as they have a better performance than Diesel engines and require less maintenance. The motor should be capable of carrying the workload required, taking into consideration the various adverse conditions under which they may have to operate; pump power requirements should be lower than the safe operating load of the motor; the characteristics of the power supply and the motor specifications should always receive attention in this respect. The choice of a suitable electric motor should always be made after consulting relevant technicians.
11. These pumps, (some of which, by design, should be operated by foot) are pumps that utilize human power. They are capable of lifting relatively low quantities of water; their capital cost is generally low; their outputs are usually adequate to meet drinking water requirements of small communities. The availability of human power for pumping depends on the cultural background of the users, on the individual's age, sex and overall health conditions, on the duration of the task and on the environment. Handpumps can be used in wells of almost any depth; reciprocating pumps which have a suction lift of less than 5 metres usually have their cylinder placed above the ground; when the static water lift is more than 5 metres the cylinder is attached to a pumping line and placed within the well; diaphragm and positive displacement pumps may also be easily adapted to handpump drives (See 7.5). Experience has shown that the success of handpumps as the main source of supply for refugee communities largely depends on the choice of pump and on correct operation and maintenance arrangements (See 11.5). Very few handpump system failures may be blamed solely on the pump: provisions for appropriate well design and construction, maintenance, project management, monitoring, supervision, water quality control and periodical project evaluations are all aspects that should be addressed when planning a handpump based water supply system. Moreover, handpump systems may only reach their highest potential of sustainability, if and only if, the user community is involved in all phases of the project, starting from the planning stage; people should recognize the need for an improved service, be able and willing to contribute in covering maintenance costs and should be willing (and trained) to manage this maintenance. These conditions are very seldom applicable in emergency refugee camps; they may, however, be applicable in rural refugee settlements or other longer term camp-like situations; this aspect requires considerable thought and attention from planners. The future of the camp and its life-span has to be explored to adapt its infrastructure to its realities since the onset of emergency assistance actions (See 5.2; 11.2). It is evident that the choice of handpumps depends not only on the price of the pump itself: pumps should be suitable for the maintenance possibilities available; they should be able to draw the required amount of water, which depends on factors such as the required lift and the planned number of users (200 people should be the largest group depending on one single handpump). When large amounts of handpumps are to be used in a single system, the standardization of the equipment to one or a few pump types should be pursued as this will have a significant impact on maintenance (See 11.15). Resistance to corrosion is a factor to take into consideration when the presence of aggressive water is either suspected or confirmed. UNHCR has considerable experience with handpump based water supply systems, some of these experiences are well documented. The Programme and Technical Support Section will use this information when assisting in planning, implementation, operation and maintenance actions related to handpump based water supply systems.
12. The final choice of the type and size of pumps to be used for human water supply purposes should be entrusted to an experienced engineer. It is always a sound practice to involve manufacturers or their representatives in the choice of pumps and pump drives. The following explanations are only intended to introduce concepts and terminology and as a way of to indicating the type of information required by technicians.
13. Total manometric head is the difference in pressure (in metres) between the pump's inlet and outlet points. This value is always higher than the actual difference in elevation between these two points; when pumping is going on, the pump needs also to overcome friction losses occurring as the water flows through the intake and outlet pipes. Appropriate tables and graphs are used to calculate "unit" friction losses; for this purpose, precise altimetric and planimetric plans containing pipeline layouts provide the best and most complete information (Fig 35).
Fig. 26 Definition of Total Manometric Head
14. Net positive suction head measures the "inability" of a centrifugal pump to create a complete vacuum (See 7.5.i.a. and 7.5.iv). If a vacuum is made in a pipe it is possible to lift water inside it to a height equivalent to the atmospheric pressure; at sea level this height is equal to 10.33 metres, at higher altitudes atmospheric pressure decreases and therefore this height decreases too; additionally friction losses within the pipes make this height even lower. The net positive suction head is dependent on the flow rate. Its variation is shown in curves normally prepared by pump manufacturers.
15. Characteristic curves: these are three type of curves that should be calculated by manufacturers for every centrifugal or axial flow pump; they are verified at test installations. The yield-head curve shows how the total manometric head that a pump is able to reach varies in accordance with variations in the pump's output. They are parabolic in shape (Fig. 27). The head at zero discharge is called "shut-off" head. As the discharge is increased, the head produced by the pump may rise or fall slightly depending on the type of pump; eventually, the head developed by the pump will drop for any further increase in discharge. The efficiency curve indicates the discharge range at which a pump works at its highest efficiency. For any given speed of operation, there is a particular discharge for which the efficiency is a maximum (the related head values may be inferred from the yield-head curve). This discharge is known as the pump's "normal discharge" or its "rated capacity" at that particular speed. In case of a need to vary the quantity of water delivered by the pump, this can be accomplished by using a regulating valve in the discharge pipeline; since maximum pump efficiency (at a given speed) occurs at a particular discharge value, this usually results in a reduced pump efficiency. The power requirements curve shows its variation for different discharge rates. For centrifugal pumps their shape is concave towards the bottom, a feature that avoids overcharging the motors or engines with varying working conditions. In the case of positive displacement pumps, power requirements at shut-off heads may be considerably higher than those under normal operating conditions, a factor that should always be taken into account during operation or maintenance activities; in this context it is worth noticing that the presence of regulating valves at the discharge pipe should be completely avoided, especially if the power source is an electric motor.
Fig. 27a Characteristic Curves (centrifugal pump)
Fig. 27b Characteristic Curves (helicoidal pump)
16. An indication of the pump type to be selected for a particular application may be obtained from Fig. 9.28. The final choice, as previously pointed out, should be left to specialized technicians.
Fig. 28 Pump Type Selection Chart