Hydraulic Ram Pumping in Rural Community Development - Rijswijk University
HYDRAULIC RAM PUMPING IN RURAL COMMUNITY DEVELOPMENTF. Zoller, J. Woudstra and M. van der WielRijswijk University of Professional Technical Education, the Netherlands and Biogas Technology Africa CC,Durban, South AfricaABSTRACTThe project started in August 2004 with the initiative ofMrs. Fuphamia Ciliza, a member of a rural communityin Inchanga, KwaZulu Natal, to set up a vegetablegarden. Maintaining the vegetable garden was hardwork; especially carrying buckets of water from theadjacent stream to the field. At that time BiogasTechnology Africa became involved via a localdevelopment worker. David Alcock of BiogasTechnology Africa supplied the project with anirrigation system based on a ram pump design hedeveloped in previous years. Maarten van der Wiel, atthat time student in his practical semester, working atBiogas Technology Africa became involved in the rampump development. Because the pump design was stillin its development phase, Maarten set the goal ofimproving the performance of the pump in terms ofdelivery flow and efficiency. His research was focusedon specifying the characteristics of the AlcockHydraulic Ram Pump and on how to tune the pump tochanging site conditions. This paper presents theoutcome of his graduation assignment.1. INTRODUCTIONRijswijk University of Professional Technical Educationbecame involved in the project because of their activitiesin the Inchanga region. They work in co-operation withKerk in Actie, a Dutch organisation that provides fundingfor development projects. The main goal is to developsustainable energy applications in co-operation with localindustry and to support the implementation. The Inchangaproject showed promising results in terms of energyconservation and social impact . The graduationresearch by Maarten van der Wiel can be seen as the finalstep in the development of the Alcock Hydraulic RamPump . The next step is finding suitable ways forcopying this successful principle where needed, whereversuitable conditions are available. Kerk in Actie haspromised financial support under the condition the requestfor project funding comes from a local NGO that acceptsthe responsibility for successful implementation.2. DESCRIPTION OF RAM PUMP ASPECTSGeneral information about the ram pump has been adoptedfrom specified literature and the website of the WorkingGroup on Development Techniques :www.student.utwente.nl/~wot“A ram pump is a water pumping device that is powered byfalling water. The pump works by using the energy ofwater running down a drive pipe to the body of the rampump. Most of the water flows back to the stream via awaste valve, a small amount of water runs to a muchgreater height. In this way, water from a stream in a valleycan 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 considerableheight”.A ram pump installation consists of a dam in a stream, adrive 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 pumpRam pumps have a cyclic pumping action that produces acharacteristic beat during operation. Due to the cyclicaction the delivery flow is pulsating. The air vessel acts as ashock absorber.The cycle can be divided into three phases: Acceleration,Delivery and Recoil.2.1 DESCRIPTION OF THE RAM PUMP CYCLEAccelerationWhen the waste valve is open, water accelerates down thedrive pipe and discharges through the open valve. Thefriction of the water flowing past the valve disc causes aDrive pipeDelivery pipeAir vesselNon-returnvalveWaste valve
force on the valve disc acting to close it. As the flowincreases it reaches a speed where the drag force issufficient to start closing the valve. Once it has begun tomove, the valve close very quickly.Figure 2: Diagram of the ram pump in acceleration phaseDeliveryAs the waste valve slams shut, it stops the flow of waterthrough it. The water that has been flowing in the drivepipe has considerable momentum which has to bedissipated. For a fraction of a second the water in the bodyof the pump is compressed, causing a large surge inpressure.This type of pressure rise is known as water hammer. Asthe pressure rises higher than the backpressure in thedelivery pipe, it forces water through the delivery valve (anon-return valve). The delivery valve stays open until thewater in the drive pipe has almost completely slowed downand the pressure in the pump body drops below the deliverypressure.The delivery valve then closes, stopping any backflow fromthe air vessel into the pump and drive pipe.Figure 3: Diagram of the ram pump in the delivery phaseRecoilDue to the water hammer, the water in the drive pipe willcompress from the waste valve further upstream, locallydecelerating the water and increasing the pressure. Thefront of this pressure rise travels upstream through the drivepipe and reaches the supply source. The expansion changesthe pressure rise in an equal but opposite pressure. Thispressure surge will travel back downstream through thedelivery pipe. The propagation of the pressure surges upand down the drive pipe, locally decelerating the velocityof the water step-wise each time they pass by, will continueuntil the velocity and kinetic energy of the water isexhausted. At this moment the pressure is low enough forthe waste valve to reopen, water begins to accelerate downthe drive pipe and out through the open waste valve,starting the cycle again.2.2 EFFICIENCY AND POWERThe power required to raise water is proportional to thewater’s flow rate multiplied by the height through which itis lifted (in a ram pump qdelivery⋅hdelivery). Similarly, thepower available from falling water is proportional to itsflow rate multiplied by the distance dropped (Qwaste⋅Hsupply).A ram pump works by transferring the power of a fallingdrive flow to a rising delivery flow.Water running down drive pipeWater is forcedthrough theopen deliveryvalveWater is dischargedto the storage tankvia the delivery pipeWater accelerates down drive pipeWater discharge viaopen waste valve
Ram pump manufacturers usually define the efficiency ofthe pump as:plysupwastedeliverydeliveryersmanufacturHQhq⋅⋅=ηHowever, this equation does not give a good representationof the efficiency of the ram pump, as it does not have adatum level. A better representation is given by Rankine, which defines the efficiency of the ram pumpinstallation as a whole and takes the water level in thesupply source as the datum:plysupwasteplysupdeliverydeliveryRankineHQ)Hh(q⋅−⋅=ηAny reference to efficiency in this paper is to the Rankineefficiency. It is useful to know the efficiency because wecan use it to predict the delivery flow of a system and tocompare two different pumps. To obtain a good deliveryflow, the efficiency of the pump should be high, thereshould be a large drive flow, and the delivery head shouldnot be too many times the drive head. The value of Rankineefficiency depends upon many factors including the designof the pump and the system being used.2.3 SUITABLE AREASAlthough all watercourses slope downwards to somedegree, the gradient of many is so small that manykilometres of feed pipe or canal would be needed to obtaina fall of water large enough to power a ram pump. The bestgeographical area for ram pumps is one which is hilly, withrapidly dropping watercourses, as can be found in theValley of a Thousand Hills.2.4 LIFE AND REALIBILITYRam pumps operated at fairly low throughput have provedextremely reliable. Some have run without stopping formany years in systems supplied with clean water from areservoir. Failures in ram pump systems often occur outsidethe pump itself – blockage of filter screens, damage topipes, sedimentation of pipes and tanks etc.2.5 TUNING TO SITE CONDITIONSAny particular ram pump is normally capable of runningunder quite a wide range of conditions. Most manufacturersquote operating ranges of drive head, drive flow anddelivery head for each pump size. When there is a limitedamount of drive water available, the waste valve has to betuned to make the most efficient use of that water toproduce the best possible output. At many sites there is aseasonal variation in the drive flow available.2.6 ECONOMIC FACTORSOne of the greatest benefits of ram pump systems is thatthey have extremely low running costs. There is no input ofexpensive petroleum fuels or electricity, making thesystems very inexpensive to operate. The purchase cost of apump, however, is usually only a fraction of the capital costof a system: drive and delivery pipe work and storage tankare usually the most expensive parts.3. NUMERICAL MODELA large number of researchers have analysed the rampump’s performance by formulating equations derivedfrom their perception of the operation of the ram pump.However, from the earliest research, to more recentresearch that use complex differential equations andcomputerised modelling to describe the unsteady flow inthe pump , little investigation has been made into theinfluence of the characteristics of the valves on theperformance of the ram pump. Therefore this researchfocuses on an analysis of the valves. It was chosen to basethe numerical analysis on rigid column theory. Thissimplification makes it possible to calculate theacceleration and speed the rigid column of water throughNewton’s second law. In this analysis the water in the drivepipe will be represented by water flowing through a controlvolume. The water in this control volume is considered tobe a rigid column. The velocity of the water flowingthrough the control volume can be determined byintegrating the acceleration of the water. The accelerationof water flowing through the control volume can be workedout with Newton’s second law: the sum of the forces equalsits mass times its acceleration. Therefore the accelerationcan be worked out by dividing the sum of the forces on thewater 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 thegravitational force on the water, minus the friction losses inthe drive pipe and drag force on the valve disc. When thedelivery valve is open the friction losses of the waste valvedisc are replaced by the friction losses of the delivery valveand the force created by the backpressure from the water inthe delivery pipe has to be subtracted from the equation.As can be concluded from the analysis of the operation ofthe ram pump, the position and motion of the valvesdetermine the period of the cycle. In a way similar to thatof the description of the acceleration and speed of the waterand the forces acting on the water column, the acceleration,speed and velocity of the waste valve disc can be workedout.This model does not include the pressure rise and dropscaused by the water hammer as the model is based on rigidcolumn theory. Therefore a logical function is included inthe model to keep the waste valve closed while the pressureis high. The logical function can be formulated as settingthe resultant force on the valve to zero when the valve discis in it top position until the velocity of the water is zero.
The valve will start to open when the pressure drops, whichis at the instant the velocity of water drops below zero.To establish the motion of the delivery valve equationssimilar to those for the waste valve could be formulated,however the motion of this valve it completely governed bywater hammer. Another logical function is included: thedelivery valve opens instantly (and completely) when thewaste valve closes and the delivery valve closes instantlywhen the waste valve starts to open.Evaluation of the numerical modelThe numerical model has been evaluated by comparing theresults with a model based on unsteady flow theory byTacke . The comparison is made by applying bothmodels on experiments by Take on the Blake Hydram. Thecomparison shows that the results derived from the modelbased on rigid column theory and the results of the modelbased on the unsteady flow theory are the same for deliveryheads below 10 m. Verification of the model with ownexperimental testing (see chapter 5) did not show goodagreement between calculated results of the model inabsolute numbers and measurements. However, bothresults show a similar influence of the input variables onthe output variables. We came to the conclusion the modelcan be used to give a qualitative explanation on theinfluence of different input variables to the ram pumpperformance.4. NUMERICAL MODEL TESTING; TUNINGTO SITE CONDITIONSThe characteristic of the ram pump system can be changedby adjusting the waste valve. During the research a newtype of waste valve has been developed in which theweight and the stroke of the valve disc can be adjusted. Thenumerical model has been used to find optimum weightand stroke for various site conditions. The variable of theamount of water available is not part of the numericalmodel, it is one of the constrains in the practicalapplication. Tests results of this numerical model lead tothe following conclusions:• The Rankine efficiency will decrease non-proportionally with an increase in valve weight;• The Rankine efficiency will decrease with anincrease in stroke length;• The delivery flow will first increase with anincrease in weight, but will eventually decreaseagain when more weight is added (the deliveryflow will have an optimum at a specific weight);• The delivery flow will increase with an increase instroke length (up to a maximum when theincreased cycle time will exceed the benefit of alarger delivery flow per cycle).5. EXPERIMENTAL TESTINGIn order to establish the exact parameters of the AlcockHydraulic Ram Pump an experimental test set-up similar tothe system that is used in Inchanga (see chapter 6) has beenmade. The parameters variable and constant:Table 1: Parameters variable and constant forexperimental testingVariable ValueMass of the waste valve 60, 176, 211, 293 and 409gramsStroke of the waste valve 5 and 10 mmConstant ValueSupply height 2,0 mDelivery height 5,0 mLength of drive pipe 8,8 mDiameter of drive pipe 42 mmDiameter of delivery pipe 20 mmDiameter of waste valve 40 mmTable 2 and 3 show the results of the measurements on theAlcock 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 AlcockHydraulic Ram Pump with valve stroke 5 mmValveweight(grams)Deliveryflow(l/min)Wasteflow(l/min)RankineEfficiency(-)Cycletime(s)60 5,75 16,4 0,53 0,46176 6,45 23,0 0,42 0,60211 7,25 24,6 0,44 0,65293 7,05 30,5 0,35 0,74409 6,75 35,5 0,29 0,91Table 3: Results of experimental testing of the AlcockHydraulic Ram Pump with valve stroke 10mmValveweight(grams)Deliveryflow(l/min)Wasteflow(l/min)RankineEfficiency(-)Cycletime(s)60 5,85 23,3 0,38 0,56176 6,55 30,4 0,32 0,72211 7,30 33,5 0,33 0,80293 8,35 40,2 0,31 0,94409 6,20 39,6 0,24 1,016. THE INCHANGA PROJECTBesides numerical model testing and experimental testing,the ram pump system has been applied and evaluated in avegetable garden in Inchanga. Biogas Technology Africasupplied this vegetable garden with a ram pump irrigationsystem. In this project the drive head is 1,5 m withdelivery head in the storage tank up to 5,0 m. Theevaluation period was one year. During the wet season theaverage delivery flow was determined at 6 l/min. Duringthe dry season the water level of the stream was extremelylow, causing the ram pump to work erratically. Adjustingthe waste valve, and thereby reducing the intake flow to thelower amount of water, solved this problem. The reduced
delivery flow was sufficient in combination with anefficient drip irrigation system. The local community tookcare of the maintenance of the ram pump; they kept thefilter at the inlet of the drive pipe clean and the put thepump system back in motion after stagnation. In case ofmajor malfunction they could contact Biogas TechnologyAfrica.The Alcock Hydraulic Ram Pump is made in kit form,including all the pipe work but excluding the storage tankand it is priced between 1000 and 1800 SAR (prices arehighly dependent on site conditions). The AlcockHydraulic Ram Pump is designed to run with drive headsof 1,0 to 3,0 m, with delivery heads of up to 25 m.7. CONCLUSIONThe Alcock Hydraulic Ram Pump proved to be a reliableram pump system in an irrigation system of a vegetablegarden in Inchanga. By adjusting the waste valve theamount of intake water could be adjusted to the limitedamount of water during the dry season.To suit site conditions the following rules for adjusting thewaste valve have been derived from numerical modeltesting:• When water is limited the weight and strokeshould be minimised;• When water is abundantly available, the strokecan be maximised and the weight can be chosen atthe optimum of the delivery curve.For both situations experimental tests have been performed.The results of experimental testing can be presented ingraphs of delivery flow and efficiency versus the valveweight for the Alcock Hydraulic Ram Pump:0,001,002,003,004,005,006,007,008,0060 176 211 293 409Valve weight (grams)Deliveryflow(l/min)0,000,100,200,300,400,500,60Rankineefficiency(-)flowefficiencyFigure 4: Measured effects of Delivery flow and Rankineefficiency versus valve weight for a stroke length of 5 mm.0,001,002,003,004,005,006,007,008,009,0060 176 211 293 409Valve weight (grams)Deliveryflow(l/min)0,000,050,100,150,200,250,300,350,40Rankineefficiency(-)flowefficiencyFigure 5: Measured effects of Delivery flow and Rankineefficiency versus valve weight for a stroke length of 10mm.The results of experimental testing can be presented in thefollowing rules for adjusting the waste valve for the AlcockHydraulic Ram Pump:When water is limited the weight and stroke should beminimised: following figure 4 the parameters are: 5 mmstroke and 60 grams weight. With a 2-m fall and a 5-mdelivery height; the delivery flow will be 5,75 l/min and theRankine efficiency will be 0,53.When water is abundantly available, the stroke can bemaximised and the weight can be chosen at the optimum ofthe delivery curve: following figure 5 the parameters are:10 mm stroke and 293 grams weight. With a 2-m fall and a5-m delivery height; the delivery flow will be 8,35 l/minand the Rankine efficiency will be 0,31.8. REFERENCES Wiel, M. van der: "The Inchanga Project HydraulicRam Pumping in Rural Community Development"Biogas Technology Africa CC/TechnischeHogeschool Rijswijk, October 2005. Wiel, M. van der: "Improving the performance of theAlcock Hydraulic Ram Pump" Biogas TechnologyAfrica CC/Technische Hogeschool Rijswijk,December 2005. Working Group on Development Techniques: “Rampumps” www.student.utwente.nl/~wotUniversity of Twente, Enschede, the Netherlands,February 2006 Take, J.H.P.M.: "Hydraulic Rams; a comparativeinvestigation. Communications on Hydraulic andGeothermical Engineering" Report no. 88-1, DelftUniversity of Technology, Department of CivilEngineering, Delft, the Netherlands, 1988. Najm, H.N., Azoury, P.H. and Piasecki, M.:"Hydraulic Ram Analysis; a new look at an oldproblem" Proceedings of the Institution ofMechanical Engineers, Vol. 213 part A, 1999, pp.127-141.
9. ACKNOWLEDGEMENTS:We would like to thank Gert de Gans and Bert Kling ofKerk in Actie, Climate Plan, for their great support of ourprojects in South Africa. And we would like to thank DavidAlcock and Biogas Technology Africa for providing meansand time for experimental testing. Thank you!CONTACT BIOGAS TECHNOLOGY AFRICA CC:David Alcock, email@example.com+27(0)317645708 +27(0)82881810810. AUTHORS:Principal Author: Fred Zoller, B Eng, senior teacher atRijswijk University of Professional Technical Education,department of Mechanical Engineering. Project manager ofthe development of Sustainable Energy/Technology,current projects in the Netherlands and Africa.Email Fred Zoller: firstname.lastname@example.orgCo-authors: Johan Woudstra, MSc. Electrical Powerengineering, dean of the faculty of Electrical engineering atRijswijk University of Professional Technical Education.Project manager of the development of SustainableEnergy/Technology, current projects in the Netherlands andAfrica.Email Johan Woudstra: email@example.comRijswijk University of Professional Technical Education:Lange Kleiweg 4, 2288 GK Rijswijk, the NetherlandsMaarten van der Wiel, B Eng, The research was carried outby Maarten van der Wiel in the context of a graduationassignment, which was successfully completed in January2006. Email Maarten vd Wiel: Maartentof@hotmail.comTel: +31612684228Presenter: The paper is presented by Fred Zoller.