Basis for the Conception and Development of a Hand Operated Piston Pump
Yemane Ghidey
Head, Research, Development and Technology Adaptation Center (RDTAC)
Basic Metals and Engineering Industries Agency
P.O. Box 1180, Addis Ababa, Ethiopia
Published in the Journal of the ESME, Vol. II, №.1, July 1998.
Reprinted with ESME permission by the African Technology Forum.
ABSTRACT
The paper presents a short account on the design and development of a conventional piston pump using a unique drive mechanism and other important fractures developed by the author. The paper then concludes by emphasizing that local production of such water abstraction devices would ensure the availability of spare parts, leading to low downtime of pumps
1. INTRODUCTION
Prior to dealing with the background for the conception of a novel piston pump designed by the author, it is advisable to briefly recount on the basic concepts of piston pumps. It is obvious that piston pumps are used to move or compress liquids or gases. The syringe represents the simplest form.
As early as the 1st century AD, a pump was made by the Greek inventor Hero. This pump had two cylinders. The pistons and its rods were formed as a single piece and their top ends were coupled to the handoperated rocking beam. Since those early days, various types of pumps suited for different applications have been developed and the search for improved types is a never ending exercise.
The RO-SHE-RA Y/G Model hand pump is a simple reciprocating pump intended to raise water from wells. The design of this pump emerged from the desire to prove the functional dependability of a highly simplified power transmission system envisaged to be used in the development of an animal driven piston pump to abstract water from wells. In the process, the practicability of the transmission system which was then of a prime concern, and the viability of the hand pump were simultaneously proved. This way, the need to develop the hand pump acquired a firm stand and in the end, the field test of the prototype became a reality.
With the aim of insuring due appreciation of the usefulness of the pump, brief comments on matters related to water and its supply conditions are presented. In the end, it is worth mentioning how thrilling and promising it is to witness the great service enjoyed from the use of the pump by rural communities at two test sites even during the performance test stages.
2. FACTS ABOUT WATER
2.1 Uses of Water
Water is the soul of existence. It has a crucial role as a natural resource for economic and social development in energy and agriculture production, and domestic and industrial utility services. In fact, cradles of civilizations and history of social development started on banks of rivers and valleys.
2.2 Forms and Distribution
Table 1 shows the forms and distribution of the total volume of water on earth.
Table 1: Forms and Distribution of Water (Ref. 1)
From Table 1, it is clearly seen that groundwater represents the largest reservoir of fresh water readily available to man.
2.3 Groundwater Utilization
At present, the development of more than 1,500 million people is dependent on groundwater which is used for irrigation, industry and other daily uses.
Some developed European countries such as England, France and Denmark use groundwater to cover a third of their total consumption. In countries such as The Netherlands and Burkina Faso, groundwater is the only source of water supply.
Some of the advantages of groundwater include:
- Commonly free from pathogenic organisms
- Absence of turbidity and color
- Effect of short draughts is not of significance
- Low susceptibility to pollution, and
- Availability in areas where there are no surface water and the like.
The two major disadvantages of groundwater though are:
- Constraints in its development, and
- In some regions, the total dissolved solid in groundwater is greater than in surface water and requires high development and operational cost.
To make use of the abundant groundwater and to benefit from the merits inherent in it, devising an appropriate handling means is imperative.
3. WATER RESOURCE AND SUPPLY IN ETHIOPIA
Ethiopia has a surface water runoff of 110.15 Ethiopia has a surface water runoff of 110.15 billion m3 per year, while its groundwater potential is estimated at 2.60 billion m3 [2]. Despite the abundance of water resource in the country, the per capita water consumption is low.
In 1992, studies on water consumption indicated that it was less than 10 liters per day per capita [2] which is insufficient from the health and hygiene point of view. The WHO standard for developing countries is 150 liters per day per capita. Over half of the Ethiopian population becomes ill, too often totally, or with longterm debilitating consequences at least, once a year, as a result of water borne diseases [3]. About half of the country’s villages are forced to use water which is potentially dangerous to health.
Among the factors that adversely influence the per capita consumption of water, the distance from the household to the water point is the most significant one. To ameliorate the problem, digging of shallow and deep wells in the proximity of settlements and provision of appropriate water lifting means is a task of utmost priority.
4. RO-SHE-RA Y/G HAND PUMP
4.1 Background
Prior to the idea to design and develop the RO-SHE-RA Y/G hand pump, another version, viz. RO-SHE-RA G, mainly designed to irrigate small plots on banks of rivers and streams during the dry seasons using animal power was developed. Encouraging test results prompted the conception of another pump namely, RO-SHE-RA MB, intended to be used to raise water from wells using an animal (horse, mule, donkey, ox, camel, etc.) power. It was for this version of pump that a highly simplified and yet durable power transmission system became an underlying condition. The reason behind this essential criterion was to avoid the need to guide and maintain correct alignment of the series of coupled rods that are usually used either as rotary or reciprocating power transmission means. In line with this objective, the use of rods was ruled out from the outset.
To meet the stringent requirement of not using rods, slim wire rope was found to be the most feasible alternative solution. Prior to trying the viability of the wire rope transmission means with the RO-SITE-RA MB version which was expected to incorporate a relatively costly drive was found to be advisable to test with a simpler hand operated one. As a result, the development of the hand pump came into being, sole objective was to experiment effective wire rope power transmission possibility.
The performance test was quite successful and the development of the hand pump in its own proper was justified.
4.2 Design Features of the Pump
As mentioned earlier, the development of the hand pump was not in its own an objective of the invention. It was primarily intended to serve as a “guinea pig” in the process of experimenting the viability of a wire rope to effect both intake and power strokes in a reciprocating pump. Eventually, the pump got its unique functional features.
4.2.1 Main Parts of the Pump
The pump comprises two main subunits. These are the highly simplified actuation system and the pump unit, shown in Fig. 1.
The actuating mechanism consists of:
- A handle
- A simple crank shaft made from detachable segments
- Guide rollers
- Wire ropes
- Chains, and
- Sprockets.
The pump unit incorporates:
- A plastic lined cast iron cylinder including flanges
- A piston
- An inlet and out let valves, and
- A mounting frame.
4.2.2 Mode of Operation
The back and forth turning of the handle results in system, it an alternating partial rotation of the crank shaft. The crank shaft effect pulls on the two wire ropes in an alternate manner and induces reciprocating although the motion. While one of the wire ropes is used to pull the piston rod in the intake (suction) direction, the second one is used to pull the piston rod in the output (discharge) direction in turns and in a synchronized way.
The chains and sprockets are used to reverse the sense of pull f the wire rope used for the power stroke. The two non-return valves ensure the flow of water in one direction.
4.3 Design Merits vs. Existing Pumps
4.3.1 Existing Hand Pumps
Before treating the merits of the pump, it would be advisable to mention some realities concerning the existing ones.
Although very limited, in terms of number and distribution (in contrast to the immense need), there are a number of hand pump types installed in both shallow and deep wells. Out of the pumps installed along the road between Addis Ababa and Zeway, most of them are out of service and some of these have been virtually abandoned. The major reasons are: high failure rates, lack of maintenance know how and unavailability of spare parts.
4.3.2 Major Inherent Advantages of the Design
The virtues of the design can be seen in terms of the fulfillment of the following three fundamental criteria.
- Durability and Maintainability
- Reproducibility and Affordability, and
- Availability of Input Material.
4.3.2.1 Durability and Maintainability
The primary aim of the design is to ensure minimization of the occurrence possibility of friction and seizure. Accordingly, the number of parts that are subject to wear and tears are very limited. Due to the highly reduced rubbing effect between sliding surfaces, any wear and tear can only take place after a long period of service/operation. The simplicity of the force transmission via a very slim (diam. 4 mm) wires rope which does not require alignment and a guiding system precision, significantly reduces the adverse effect of friction. Apart from the flexibility, additional advantages of the wire ropes include silent operation, low weight for a given capacity, and ease of installation and maintenance, leading to a long and trouble free service life.
Not only the wear and tear chances for parts are very low, but accessibility of all parts facilitates easy maintenance. Moreover, because of the low friction of the system, the effort needed to operate the pump is very minimal.
Besides the pump’s simplicity of maintenance, the fact that all parts are either locally manufactured or available as standard items for various applications, minimizes the downtime of the pump after failure. Hence, sustainability of the pumping system is ensured.
4.3.2.2 Reproducibility and Affordability
To ensure ease of production and price competitiveness, the design has considered the commonest as well as cost efficient production techniques. The degree of precision required for the manufacturing of the parts is low and can be fabricated in most metal shops. Since the raw materials and standard parts are readily available n the market, they do not pose any constraint in the production of the pump. The combined effect of the aforementioned facts forms the basis for the price competitiveness and affordability of the pump.
In conventional pumps, water flows over the power transmission rods, requiring the use of corrosion resistant pump rods. This entails higher cost. In the RO-SHE-RA Y/G pump, there is no contact between the pumped water and the power transmission wire ropes. Hence, resistance to corrosion is not an issue of concern. The cost of the pump rods in conventional pumps is much higher than the wire rope used in this pump.
Considering the number of people who can be served by one pump and the benefits that can be derived in contrast with the share of the initial investment and the maintenance cost per head, the issue of affordability becomes quite evident.
4.3.2.3 Input Materials
The raw materials input for the production of the pump, largely comprise common structural steels, used by metal fabrication shops for various products. As a result, they are readily available on the local market. In fact, most of these raw materials are produced domestically. The cast iron parts can also be produced in small size foundries.
All of the required standard parts are among the most common types that are used in different machines and equipment and are not customs engineered for the pump.
5. STATUS OF THE PUMP
Before embarking on batch or commercial scale production of the pump, obtaining successful field test results is mandatory. To this effect, two units have been installed at two localities near the town of Zeway. The first unit installed in a well of 11 meters pumping head is operational since April 1998. The second pump is installed in a well having a depth of 33 meters, and has been in operation since June 1998.
The operation of the pump is smooth and silent. The effort required to operate the pump is much lower compared to other pumps with similar capacities.
6. CONCLUSION
Accesses to safe water in copious amount and provision of sanitation facilities are measures of development Absence of potable water in the proximity of settlements among other things, results in an arduous and time-consuming task of water fetching, especially to women and children who are the main collectors of water.
In some parts of Ethiopia, women expend as much as 85 percent of their daily energy intakes in fetching water. As a result, many women suffer from anemia and other health problems. The RO-SHE-RA Y/G pump is hoped to play a pivotal role, in the endeavor to reduce the grave problem of water supply in the rural communities of Ethiopia.
The development of the pump, as an indigenous Ethiopian technology, has demonstrated that there is yet untapped national potential in the field of design and manufacture.
As F.L. Wright said, “I know the price of success dedication, hard work and unremitting devotion to the things you want to see happen.” It is thrilling to witness the services enjoyed by the users of the pumps installed for test purposes.
REFERENCES
1. Water and Development, Vol.2, №7, March 1998.
2. National Workshop on Technical Papers, presentation, March 1997.
3. Water Supply and Sewerage Authority Bulletin, September 1992.
