Pumping facilities are required wherever water is stored at or below ground level. Conventionally powered pumps, such as diesel and electric pumps, require readily available sources of fossil fuels or electricity. In countries where access to conventional energy is limited by cost or sources of supply, pumps powered by non-conventional energy systems may provide an alternative.
Several types of pumps powered by non-conventional energy have potential utility in Latin American countries. Different types of pumps have been tested with mechanisms fabricated from local materials, using limited fabrication skills and available energy sources. They include the following:
· Hydraulic Pumps
The hydraulic pump or water wheel is driven by the energy of the moving water in a river. The circular movement of the wheel is transmitted via a 1 in. diameter shaft, fitted with an offset arm, to the piston of a small pump. In Peru, typical pumps of this kind have capacities of 0.2 to 6.0 l/sec.
· Hydraulic Ram Pumps
The hydraulic ram is a simple pump, in universal use, driven by the energy produced by differences in hydrostatic pressure, which activates a valve and raises the water. A ram can pump approximately one tenth of the received water volume to a height ten times greater than the intake.
· Rope Pumps
The rope pump consists of a loop of nylon rope with rubber gaskets attached to it. The gaskets slip through the interior of a PVC pipe 1 in. in diameter. The rope pump is operated manually by rotating a wheel, which pulls the rope through the pipe. The effort necessary to turn the handle depends on the length of the pipe and the depth of the water. The length of a pipe 1 in. in diameter can range from 1 m to 12 m. A schematic of a rope pump manufactured in Bolivia is shown in Figure 14.
· Hand Pumps
There are many different variants of the hand pump, with different designs that can be locally built or purchased ready-made. Hand pump systems can be installed below or above ground. Field experiments have been conducted in Bolivia using the INTI direct-action hand pump, the Bolivian equivalent of the Tara pump developed for use in Bangladesh. This pump, as used in Bolivia, has a lifting capacity of up to 15 m, and a ratio of 0.7:1 between the diameters of the interior pipe, which functions as a piston, and the exterior pipe, which conveys the water to the required height, as shown in Figure 15.
· Windmill Pumps
The windmill pump is operated by making use of wind energy. The energy generated by the wind moves a rotor which translates to the vertical movement of a piston in the pump. Water is then drawn up through the internal pipe, reaching heights of up to 7 m, depending on the tower size. Windmill-powered pumps can lift water to a height of 20 m. The pump capacity is a function of wind speed and the suction elevation. At wind speeds of 4 m/s, pump capacities range between 0.5 and 1.5 Vs over suction heights of 20 m and 5 m, respectively. For the same suction heights but twice the wind speed, the capacities range between 3.2 and 4.0 l/s.
Figure 14: Schematic of a Rope Pump.
Source: Freddy Camacho Villegas, Institute of Hydraulics and Hydrology, University of San Andrés (UMSA), La Paz, Bolivia.
Figure 15: Schematic of a Direct-Action Hand Pump.
Source: Freddy Camacho Villegas, Institute of Hydraulics and Hydrology, University of San Andrés (UMSA), La Paz, Bolivia.
· Photovoltaic-Powered Pumps
In spite of the abundance of solar radiation in Honduras, photovoltaic solar energy has not been used as much as expected. A technical assistance program to develop water sources for human consumption on Roatán Island off the Honduran coast used solar panels and a photovoltaic-powered pump system to raise the water to a 13 000 gal, reserve water storage tank. The pumping system consisted of a submersible electric pump directly connected to a photovoltaic cell system and operated continuously whenever there was enough sunshine.
Extent of Use
Demand for hand pumps in individual countries in Latin America and the Caribbean is potentially on the order often of thousands. However, the relatively small, localized markets where this technology is most in demand may not attract the large manufacturers. Thus, there are excellent opportunities for small- and medium-sized firms providing pump sales and servicing. The types of pumps used vary with the applications desired, although their use is widespread.
The use of hydraulic pumps in Honduras is limited to the southern, northwestern, and northern sections of the country, where rivers of sufficient size are located. In contrast, they are widely used in Peru.
Hydraulic ram pumps, operating in lower volume river flows, have been adapted for use in numerous areas of Honduras, including the central zone and the eastern, western, and northwestern sections. This technology is functional for use in rural development, primarily for domestic use, livestock watering, and crop irrigation.
Rope pumps, because of their simplicity of design and ease of construction, are used in many countries. They are usually built locally by the individual operators. These pumps are used extensively in Honduras, Peru, Haiti, and Bolivia.
Windmill-driven pumps are used relatively rarely. Although very functional, they are mainly used for domestic water supply and cattle watering on a small scale. This technology has been used in Peru and the central region of Panama. Windmill pumps of similar design have been used in Honduras and in Centro Las Gavistas, Colombia. In Peru, windmill-powered pumps have 12 arms, 5 m in diameter, which can reach 30 rpm at a height of 6m above the ground. The pump mechanism consists of a reciprocating piston 6 in. in diameter, a cylinder, a casing, and a discharge pipe.
Photovoltaic technology can provide electric power to drive water pumps in areas with abundant insolation. However, its high cost and sophisticated technical requirements limit its use. Most individuals, communities and institutions would find this technology too expensive at its present level of development. Roatán Island, Honduras, in the Caribbean Sea, is not fully served by conventional sources of electricity and for this reason is one of the few places in Honduras where solar pump technology is utilized; four systems provide service to four communities. Photovoltaic-powered pumps have also been tested in Haiti.
Operation and Maintenance
Operation of most of these non-conventional systems is relatively simple, although most require additional labor. Some of the pumps, like the hand and rope pumps, require constant attention to keep them operating efficiently. Most of the pumps require the use of anti-corrosive paints to protect the exposed metal parts, and frequent oiling (twice a month) of the parts of the pump where friction between different parts can be expected. However, it is important to avoid the use of heavy-metal-based (e.g., lead paints) and to avoid contaminating the insides of the pumps with hydrocarbon residues, especially if the water is to be used for human consumption. Such contamination can lead to chronic public health problems. In general the following factors should be considered in the design of a hand pump system:
· Non-wearing parts of the pump must be durable and reliable enough to last at least ten years.
· The wearing parts should be readily accessible, require no special skills to service, be inexpensive to replace, and be of consistent high quality to ensure interchangeability.
· A below-ground system should be as light as possible so that it can be extracted when necessary, even from deep wells, without the need for specialized lifting equipment.
· The impact of corrosion should be minimized by using materials which are inherently corrosion-resistant.
· Pumps should be able to be easily maintained by caretakers drawn from the community who have minimal skills, using a few simple tools and with modest training; this generally means that the pumps should be manufactured, or be capable of being manufactured, in the country of use, primarily to ensure the availability of spare parts.
· Pumps and spare parts should be cost-effective.
· Boreholes must be designed and constructed in a manner appropriate to the capabilities of the pump to be used and suitable for use under local conditions.
· Pumps should be acceptable to the users; i.e., used consistently, viewed positively with few complaints, and not liable to be vandalized.
These features are applicable to the design of all pumping systems.
The need for maintenance varies with the type of pump, from pumps requiring minimal maintenance to pumps requiring almost constant upkeep. The hydraulic pump, which is impelled by the river stream, requires very little maintenance. On the other hand, maintenance is probably the single most important element in hand pump operation. To address this issue, the concept of village-level operation and maintenance (VLOM) was developed to provide local villagers with the option of maintaining the pumps at the community level. The principles of VLOM are embodied in the design criteria set out above. In meeting these criteria, the manufacturing processes and raw materials required for pump maintenance should be already available in the country of use or should be capable of developing as self-supporting, commercial enterprises there.
The four photovoltaic-powered pumping systems in operation on Roatán Island were installed in 1986. Their operation and maintenance are performed by the residents of the communities using the pumps. It is usually a very simple task, consisting of cleaning of the solar panels, protecting the wells from contamination, and occasionally replacing the submersible electric pumps when they fail. These submersible pumps are the component of the system which fails most frequently. During a ten-year period, two pumps have been damaged in each community, requiring an average of a new pump every five years. The rest of the photovoltaic system has only suffered from some corrosion due to the saline environment on the island. In addition, some of the photovoltaic panels have lost some of their efficiency, apparently as a result of construction defects. It is significant to note that, even though two of the communities now have access to electricity service, they continue to power their water supply system with the solar panels.
Level of Involvement
Few governments have participated in the application of non-conventional energy sources to the pumping of water. Most pumping systems using such sources have been developed by local communities in cooperation with NGOs and financed by external agencies, such as USAID. Likewise, whenever system operators have needed technical and financial assistance (for example, to replace a pump), NGOs generally have provided the necessary technical assistance, and financial support has been forthcoming from organizations such as the U.S. Peace Corps and Volunteers in Technical Assistance (VITA), and, in Honduras, the Sandia National Laboratory of the United States.
The hydraulic ram pump locally manufactured in Honduras costs approximately $200 in local retail establishments, excluding installation costs. The estimated costs of variously sized hydraulic ram pumps in Peru are shown in Table 4. Hydraulic ram pump design criteria should include the volume of water available, lifting height, water gradient, and pumping distance.
Table 4 Estimated Cost ($) of Hydraulic Ram Pumps
Source: Catholic University of Peru.
The rope pump has an average cost of less than $250, excluding installation and well digging. Materials are very simple and may be locally acquired.
The windmill-driven pump is estimated to cost between $800 and $1 000, excluding installation and well excavation, and is available only from specialized suppliers. The manufacturing costs of three different models used in Peru were estimated at $2 700, $3 500, and $6 000 for windmill pumps with a rotor diameter of 3.5 m, 5 m and 10 m, respectively. Installation and maintenance costs were estimated at 15% of the construction cost.
Economics is the principal constraint on the use of the photovoltaic energy technology. Use of this technology usually requires a large initial investment. The difficulties of communication and transportation in rural areas, combined with the relatively few specialized suppliers, increases the initial cost of photovoltaic-powered systems significantly, although recent technological advances are reducing it.
Effectiveness of the Technology
The hydraulic pump can lift water to a maximum height of 25 m. These pumps perform favorably in comparison with other, similar technologies. At river velocities of 2.0 m/sec and discharges of 0.40 m3/sec, a hydraulic pump can yield enough water to irrigate an area of approximately 1 800 m2 of crops. Alternatively, the pump can supply 72 dwellings and a population of 500 persons or a cattle shed of 140 cows, with water for domestic or stock-watering use.
The efficiency of the windmill-powered pumps varies directly in proportion to the speed of the wind. At wind speeds ranging from 5 to 18 km/hr, the daily yield varies from 3 to 12 m3/day, respectively, assuming an average of 6 working hours/day.
This technology is suitable for use in regions where fuel or electricity is unavailable. For this reason, these alternatively powered pumps are well suited for use in the rural areas of most Latin American and Caribbean countries.
In general, the advantages common to these types of pumping systems are that they do not use combustible fuels, have a low cost to manufacture and are inexpensive to purchase, and incur minimal maintenance requirements. Each of these pumps has a negligible environmental impact. Specific advantages of each type are as follows:
· The technology works 24 hours a day.
· It is usable for pressurized-water irrigation systems (microjet and drip irrigation).
Hydraulic ram pump
· The technology produces a high yield.
· It can be coupled with most water irrigation systems.
· Construction does not require skilled labor.
· The technology has a minimal potential for water contamination.
· The design is proper for the tropics.
· Windmill arms do not need protection against storms.
· The technology is easy to install.
· The pump uses a readily available energy source.
· The technology requires little maintenance.
· It is clean, thereby reducing the possibility of contamination.
· No combustible fuels are needed.
· It is easy to install in a relatively short period of time.
· The technology is simple and reliable.
· The solar panels have a long life expectancy.
· It may be incorporated into a flexible, modular system which adapts easily to community needs.
· Hydraulic pumps and hydraulic ram pumps must be located close to river channels, which makes them vulnerable to flood damage unless the equipment can be removed at short notice.
· The use of hydraulic pumps and hydraulic ram pumps is limited to the irrigation of small areas.
· The rope pump cannot raise water far above the surface of the well; it is limited to wells of less than 8m in depth.
· Windmill-powered pumps are not recommended for agricultural purposes because water extraction is difficult at depths of greater than 20 m.
· Repairs to photovoltaic-powered pumps, particularly in rural areas, may be dependent on imported parts; inventories of critical spares are needed to avoid stoppages due to breakdowns and waiting times while replacements are found.
· The initial cost of a photovoltaic system is considerable, and the regular maintenance may be extensive and costly if storage batteries are involved.
With the exception of the photovoltaic-powered pumps, the alternative energy sources used to power the pumps are traditional and well accepted by the communities. At this time, the cost of solar-energy-powered systems limits the level of community acceptance.
Further Development of the Technology
Improvements in pump design are needed to increase the efficacy of these technologies. For hydraulic pumps, these include the use of a double turbine to increase the torque from the main axis so that pumps of greater capacity can be used. The rope pump can be improved through changes in the construction and operation of the pumps, particularly in rural areas, to increase the discharge height of the pump. Aspects of hand pumps also need improvement. Some common needs include:
· Development of quality standards and quality control procedures, including simple tests, for PVC pipes manufactured in developing countries.
· Development of design guidelines for plastic, riser main assemblies, including suggested material and dimensional specifications.
· Research on alternative materials for use as non-sliding bearings in practical designs.
· Investigation of the design and manufacture of plastic pump elements to reduce costs and improve the reliability of pump cylinders.
· Development of practical designs for sealless pistons and solid state valves.
· Assessment and development of additional methods for protecting cylinders against sand contamination.
· Development of improved designs for pump rod and riser and connectors.
· Assessment of techniques for preventing corrosion, including cathodic protection, plating techniques, and coating with plastics or rubber.
· Development of reliable, easy-to-release couplings for pump nodes.
Freddy Camacho Villegas, Instituto de Hidráulica e Hidrología (IHH), Universidad Mayor de San Andrés (UMSA), Calle 30 s/n, Cota Cota, Casilla Postal No. 699, La Paz, Bolivia. Tel. (591-2)79-5724. Fax (591-2)79-2622.
Maria Concepción Donoso, Directora, Centro del Agua del Trópico Húmedo para América Latina y el Caribe (CATHALAC), Apartado Postal 873372, Panamá 7, Panamá. Tel (507)228-7944/228-7072. Fax (507)228-3311. E-mail: [email protected].
Jose Luis Monroy C, Instituto de Hidráulica e Hidrología (IHH), Universidad Mayor de San Andrés (UMSA), Calle 30 s/n, Cota Cota, Casilla de Correo 699, La Paz, Bolivia. Tel. (591-2)79-5724/79-5725. Fax (591-2)79-2622.
Rebén Ledezma, Centro de Promoción y Cooperación Campesina YUNTA, Calle Colombia 257, La Paz, Bolivia. Tel. (591-2)35-3526.
Miguel Hadzich Marín, Coordinador de Investigaciones, Sección Ingeniería Mecánica, Equipos de Bombeo no Convencionales, Pontificia Universidad Católica del Perú, Ave. Universitaria, Cuadra 18, San Miguel, Lima, Perú. Tel. (51-1)462-2540, anexo 263. Fax (51-1)461-1785.
Alba Luz Hernández, Jefe del Departamento de Riego, Dirección General de Recursos Hídricos, Tegucigalpa, Honduras. Tel. (504)32-6250. Fax (504)32-1828.
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