HYDRAULIC RAM PUMPING IN RURAL COMMUNITY DEVELOPMENT F. Zoller, J. Woudstra and M. van der Wiel Rijswijk University of Professional Technical Education, the Netherlands and Biogas Technology Africa CC,

Durban, South Africa ABSTRACT The project started in August 2004 with the initiative of Mrs. Fuphamia Ciliza, a member of a rural community in Inchanga, KwaZulu Natal, to set up a vegetable garden. Maintaining the vegetable garden was hard work; especially carrying buckets of water from the adjacent stream to the field. At that time Biogas Technology Africa became involved via a local development worker. David Alcock of Biogas Technology Africa supplied the project with an irrigation system based on a ram pump design he developed in previous years. Maarten van der Wiel, at that time student in his practical semester, working at Biogas Technology Africa became involved in the ram pump development. Because the pump design was still in its development phase, Maarten set the goal of improving the performance of the pump in terms of delivery flow and efficiency. His research was focused on specifying the characteristics of the Alcock Hydraulic Ram Pump and on how to tune the pump to changing site conditions. This paper presents the outcome of his graduation assignment. 1. INTRODUCTION Rijswijk University of Professional Technical Education became involved in the project because of their activities in the Inchanga region. They work in co-operation with Kerk in Actie, a Dutch organisation that provides funding for development projects. The main goal is to develop sustainable energy applications in co-operation with local industry and to support the implementation. The Inchanga project showed promising results in terms of energy conservation and social impact [1]. The graduation research by Maarten van der Wiel can be seen as the final step in the development of the Alcock Hydraulic Ram Pump [2]. The next step is finding suitable ways for copying this successful principle where needed, wherever suitable conditions are available. Kerk in Actie has promised financial support under the condition the request for project funding comes from a local NGO that accepts the responsibility for successful implementation. 2. DESCRIPTION OF RAM PUMP ASPECTS General information about the ram pump has been adopted from specified literature and the website of the Working Group on Development Techniques [3]: www.student.utwente.nl/~wot “A ram pump is a water pumping device that is powered by falling water. The pump works by using the energy of water running down a drive pipe to the body of the ram

pump. Most of the water flows back to the stream via a waste valve, a small amount of water runs to a much greater height. In this way, water from a stream in a valley can be pumped to an irrigation scheme on the hillside. Wherever a fall of water of at least 1,0 m can be obtained, the ram pump can be used as a comparatively cheap, simple and reliable means of raising water to considerable height”. A ram pump installation consists of a dam in a stream, a drive pipe that carries the water to a waste valve, a non-return delivery valve, an air vessel and a delivery pipe.

Figure 1: Diagram of the ram pump Ram pumps have a cyclic pumping action that produces a characteristic beat during operation. Due to the cyclic action the delivery flow is pulsating. The air vessel acts as a shock absorber. The cycle can be divided into three phases: Acceleration, Delivery and Recoil. 2.1 DESCRIPTION OF THE RAM PUMP CYCLE Acceleration When the waste valve is open, water accelerates down the drive pipe and discharges through the open valve. The friction of the water flowing past the valve disc causes a

Drive pipe

Delivery pipe Air vessel Non-return valve Waste valve

force on the valve disc 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 close very quickly.

Figure 2: Diagram of the ram pump in acceleration phase Delivery As the waste 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 the 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 the backpressure in the delivery pipe, 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 drops below the delivery pressure. The delivery valve then closes, stopping any backflow from the air vessel into the pump and drive pipe.

Figure 3: Diagram of the ram pump in the delivery phase Recoil Due to the water hammer, the water in the drive pipe will compress from the waste valve further upstream, locally decelerating the water and increasing the pressure. The front of this pressure rise travels upstream through the drive pipe and reaches the supply source. The expansion changes the pressure rise in an equal but opposite pressure. This pressure surge will travel back downstream through the delivery pipe. The propagation of the pressure surges up and down the drive pipe, locally decelerating the velocity of the water step-wise each time they pass by, will continue until the velocity and kinetic energy of the water is exhausted. At this moment the pressure is low enough for the waste valve to reopen, water begins to accelerate down the drive pipe and out through the open waste valve, starting the cycle again. 2.2 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 qdelivery⋅hdelivery). Similarly, the power available from falling water is proportional to its flow rate multiplied by the distance dropped (Qwaste⋅Hsupply). A ram pump works by transferring the power of a falling drive flow to a rising delivery flow.

Water running down drive pipe

Water is forced through the open delivery valve

Water is discharged to the storage tank via the delivery pipe

Water accelerates down drive pipe

Water discharge via open waste valve

Ram pump manufacturers usually define the efficiency of the pump as:

plysupwaste

deliverydeliveryersmanufactur HQ

hq⋅

⋅=η

However, this equation does not give a good representation of the efficiency of the ram pump, as it does not have a datum level. A better representation is given by Rankine [4], which defines the efficiency of the ram pump installation as a whole and takes the water level in the supply source as the datum:

plysupwaste

plysupdeliverydeliveryRankine HQ

)Hh(q⋅

−⋅=η

Any reference to efficiency in this paper is to the Rankine efficiency. 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. 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 Rankine efficiency depends upon many factors including the design of the pump and the system being used. 2.3 SUITABLE AREAS Although all watercourses slope downwards to some degree, the gradient of many is so small that many kilometres of feed pipe or canal would be needed to obtain a fall of water large enough to power a ram pump. The best geographical area for ram pumps is one which is hilly, with rapidly dropping watercourses, as can be found in the Valley of a Thousand Hills. 2.4 LIFE AND REALIBILITY Ram pumps operated at fairly low throughput have proved extremely reliable. Some have run without stopping for many years in systems supplied with clean water from a reservoir. Failures in ram pump systems often occur outside the pump itself – blockage of filter screens, damage to pipes, sedimentation of pipes and tanks etc. 2.5 TUNING TO 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, drive flow and delivery head for each pump size. When there is a limited amount of drive water available, the waste 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.

2.6 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 of the capital cost of a system: drive and delivery pipe work and storage tank are usually the most expensive parts. 3. NUMERICAL MODEL A large number of researchers have analysed the ram pump’s performance by formulating equations derived from their perception of the operation of the ram pump. However, from the earliest research, to more recent research that use complex differential equations and computerised modelling to describe the unsteady flow in the pump [5], little investigation has been made into the influence of the characteristics of the valves on the performance of the ram pump. Therefore this research focuses on an analysis of the valves. It was chosen to base the numerical analysis on rigid column theory. This simplification makes it possible to calculate the acceleration and speed the rigid column of water through Newton’s second law. In this analysis the water in the drive pipe will be represented by water flowing through a control volume. The water in this control volume is considered to be a rigid column. The velocity of the water flowing through the control volume can be determined by integrating the acceleration of the water. The acceleration of water flowing through the control volume can be worked out with Newton’s second law: the sum of the forces equals its mass times its acceleration. Therefore the acceleration can be worked out by dividing the sum of the forces on the water column by its mass. The sum of forces depends on the position of the valves. When the waste valve is open the resultant force is the gravitational force on the water, minus the friction losses in the drive pipe and drag force on the valve disc. When the delivery valve is open the friction losses of the waste valve disc are replaced by the friction losses of the delivery valve and the force created by the backpressure from the water in the delivery pipe has to be subtracted from the equation. As can be concluded from the analysis of the operation of the ram pump, the position and motion of the valves determine the period of the cycle. In a way similar to that of the description of the acceleration and speed of the water and the forces acting on the water column, the acceleration, speed and velocity of the waste valve disc can be worked out. This model does not include the pressure rise and drops caused by the water hammer as the model is based on rigid column theory. Therefore a logical function is included in the model to keep the waste valve closed while the pressure is high. The logical function can be formulated as setting the resultant force on the valve to zero when the valve disc is in it top position until the velocity of the water is zero.

The valve will start to open when the pressure drops, which is at the instant the velocity of water drops below zero. To establish the motion of the delivery valve equations similar to those for the waste valve could be formulated, however the motion of this valve it completely governed by water hammer. Another logical function is included: the delivery valve opens instantly (and completely) when the waste valve closes and the delivery valve closes instantly when the waste valve starts to open. Evaluation of the numerical model The numerical model has been evaluated by comparing the results with a model based on unsteady flow theory by Tacke [4]. The comparison is made by applying both models on experiments by Take on the Blake Hydram. The comparison shows that the results derived from the model based on rigid column theory and the results of the model based on the unsteady flow theory are the same for delivery heads below 10 m. Verification of the model with own experimental testing (see chapter 5) did not show good agreement between calculated results of the model in absolute numbers and measurements. However, both results show a similar influence of the input variables on the output variables. We came to the conclusion the model can be used to give a qualitative explanation on the influence of different input variables to the ram pump performance. 4. NUMERICAL MODEL TESTING; TUNING

TO SITE CONDITIONS The characteristic of the ram pump system can be changed by adjusting the waste valve. During the research a new type of waste valve has been developed in which the weight and the stroke of the valve disc can be adjusted. The numerical model has been used to find optimum weight and stroke for various site conditions. The variable of the amount of water available is not part of the numerical model, it is one of the constrains in the practical application. Tests results of this numerical model lead to the following conclusions:

• The Rankine efficiency will decrease non-proportionally with an increase in valve weight;

• The Rankine efficiency will decrease with an increase in stroke length;

• The delivery flow will first increase with an increase in weight, but will eventually decrease again when more weight is added (the delivery flow will have an optimum at a specific weight);

• The delivery flow will increase with an increase in stroke length (up to a maximum when the increased cycle time will exceed the benefit of a larger delivery flow per cycle).

5. EXPERIMENTAL TESTING In order to establish the exact parameters of the Alcock Hydraulic Ram Pump an experimental test set-up similar to

the system that is used in Inchanga (see chapter 6) has been made. The parameters variable and constant: Table 1: Parameters variable and constant for

experimental testing Variable Value Mass of the waste valve 60, 176, 211, 293 and 409

grams Stroke of the waste valve 5 and 10 mm Constant Value Supply height 2,0 m Delivery height 5,0 m Length of drive pipe 8,8 m Diameter of drive pipe 42 mm Diameter of delivery pipe 20 mm Diameter of waste valve 40 mm

Table 2 and 3 show the results of the measurements on the Alcock Hydraulic Ram Pump in the experimental testing. Each result is an average of at least 5 measurements. Table 2: Results of experimental testing of the Alcock

Hydraulic Ram Pump with valve stroke 5 mm Valve weight (grams)

Delivery flow (l/min)

Waste flow (l/min)

Rankine Efficiency (-)

Cycle time (s)

60 5,75 16,4 0,53 0,46 176 6,45 23,0 0,42 0,60 211 7,25 24,6 0,44 0,65 293 7,05 30,5 0,35 0,74 409 6,75 35,5 0,29 0,91

Table 3: Results of experimental testing of the Alcock

Hydraulic Ram Pump with valve stroke 10 mm

Valve weight (grams)

Delivery flow (l/min)

Waste flow (l/min)

Rankine Efficiency (-)

Cycle time (s)

60 5,85 23,3 0,38 0,56 176 6,55 30,4 0,32 0,72 211 7,30 33,5 0,33 0,80 293 8,35 40,2 0,31 0,94 409 6,20 39,6 0,24 1,01

6. THE INCHANGA PROJECT Besides numerical model testing and experimental testing, the ram pump system has been applied and evaluated in a vegetable garden in Inchanga. Biogas Technology Africa supplied this vegetable garden with a ram pump irrigation system. In this project the drive head is 1,5 m with delivery head in the storage tank up to 5,0 m. The evaluation period was one year. During the wet season the average delivery flow was determined at 6 l/min. During the dry season the water level of the stream was extremely low, causing the ram pump to work erratically. Adjusting the waste valve, and thereby reducing the intake flow to the lower amount of water, solved this problem. The reduced

delivery flow was sufficient in combination with an efficient drip irrigation system. The local community took care of the maintenance of the ram pump; they kept the filter at the inlet of the drive pipe clean and the put the pump system back in motion after stagnation. In case of major malfunction they could contact Biogas Technology Africa. The Alcock Hydraulic Ram Pump is made in kit form, including all the pipe work but excluding the storage tank and it is priced between 1000 and 1800 SAR (prices are highly dependent on site conditions). The Alcock Hydraulic Ram Pump is designed to run with drive heads of 1,0 to 3,0 m, with delivery heads of up to 25 m. 7. CONCLUSION The Alcock Hydraulic Ram Pump proved to be a reliable ram pump system in an irrigation system of a vegetable garden in Inchanga. By adjusting the waste valve the amount of intake water could be adjusted to the limited amount of water during the dry season. To suit site conditions the following rules for adjusting the waste valve have been derived from numerical model testing:

• When water is limited the weight and stroke should be minimised;

• When water is abundantly available, the stroke can be maximised and the weight can be chosen at the optimum of the delivery curve.

For both situations experimental tests have been performed. The results of experimental testing can be presented in graphs of delivery flow and efficiency versus the valve weight for the Alcock Hydraulic Ram Pump:

0,001,002,003,004,005,006,007,008,00

60 176 211 293 409Valve weight (grams)

Del

iver

y flo

w (l

/min

)

0,00

0,10

0,20

0,30

0,40

0,50

0,60

Ran

kine

eff

icie

ncy

(-)

flowefficiency

Figure 4: Measured effects of Delivery flow and Rankine efficiency versus valve weight for a stroke length of 5 mm.

0,001,002,003,004,005,006,007,008,009,00

60 176 211 293 409Valve weight (grams)

Del

iver

y flo

w (l

/min

)

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

Ran

kine

eff

icie

ncy

(-)

flow

efficiency

Figure 5: Measured effects of Delivery flow and Rankine efficiency versus valve weight for a stroke length of 10 mm. The results of experimental testing can be presented in the following rules for adjusting the waste valve for the Alcock Hydraulic Ram Pump: When water is limited the weight and stroke should be minimised: following figure 4 the parameters are: 5 mm stroke and 60 grams weight. With a 2-m fall and a 5-m delivery height; the delivery flow will be 5,75 l/min and the Rankine efficiency will be 0,53. When water is abundantly available, the stroke can be maximised and the weight can be chosen at the optimum of the delivery curve: following figure 5 the parameters are: 10 mm stroke and 293 grams weight. With a 2-m fall and a 5-m delivery height; the delivery flow will be 8,35 l/min and the Rankine efficiency will be 0,31. 8. REFERENCES [1] Wiel, M. van der: "The Inchanga Project Hydraulic

Ram Pumping in Rural Community Development" Biogas Technology Africa CC/Technische Hogeschool Rijswijk, October 2005.

[2] Wiel, M. van der: "Improving the performance of the Alcock Hydraulic Ram Pump" Biogas Technology Africa CC/Technische Hogeschool Rijswijk, December 2005.

[3] Working Group on Development Techniques: “Ram pumps” www.student.utwente.nl/~wot

University of Twente, Enschede, the Netherlands, February 2006

[4] Take, J.H.P.M.: "Hydraulic Rams; a comparative investigation. Communications on Hydraulic and Geothermical Engineering" Report no. 88-1, Delft University of Technology, Department of Civil Engineering, Delft, the Netherlands, 1988.

[5] Najm, H.N., Azoury, P.H. and Piasecki, M.: "Hydraulic Ram Analysis; a new look at an old problem" Proceedings of the Institution of Mechanical Engineers, Vol. 213 part A, 1999, pp. 127-141.

9. ACKNOWLEDGEMENTS: We would like to thank Gert de Gans and Bert Kling of Kerk in Actie, Climate Plan, for their great support of our projects in South Africa. And we would like to thank David Alcock and Biogas Technology Africa for providing means and time for experimental testing. Thank you! CONTACT BIOGAS TECHNOLOGY AFRICA CC: David Alcock, baekey@saol.com +27(0)317645708 +27(0)828818108 10. AUTHORS: Principal Author: Fred Zoller, B Eng, senior teacher at Rijswijk University of Professional Technical Education, department of Mechanical Engineering. Project manager of the development of Sustainable Energy/Technology, current projects in the Netherlands and Africa. Email Fred Zoller: f.c.m.zoller@thrijswijk.nl Co-authors: Johan Woudstra, MSc. Electrical Power engineering, dean of the faculty of Electrical engineering at Rijswijk University of Professional Technical Education. Project manager of the development of Sustainable Energy/Technology, current projects in the Netherlands and Africa. Email Johan Woudstra: j.b.woudstra@thrijswijk.nl Rijswijk University of Professional Technical Education: Lange Kleiweg 4, 2288 GK Rijswijk, the Netherlands Maarten van der Wiel, B Eng, The research was carried out by Maarten van der Wiel in the context of a graduation assignment, which was successfully completed in January 2006. Email Maarten vd Wiel: Maartentof@hotmail.com Tel: +31612684228 Presenter: The paper is presented by Fred Zoller.