1

Mini-project report

Design of a Water Lifting Device for

Rural Communities in Malawi

Alex Buckman –

alex.buckman@sheffield.ac.uk

19/05/2012

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CONTENTS Introduction ............................................................................................................................................................ 3

Aims ........................................................................................................................................................................ 3

Design Objectives and Specifications ................................................................................................................. 3

Specifications ...................................................................................................................................................... 4

Generation of Ideas ................................................................................................................................................ 4

Existing Technologies .......................................................................................................................................... 4

Suction Pump Technologies ............................................................................................................................ 5

Design Ideas ........................................................................................................................................................ 5

Ideas ................................................................................................................................................................... 5

Selecting a Solution ................................................................................................................................................ 6

Design Considerations ............................................................................................................................................ 7

Mechanical Analysis and Materials ........................................................................................................................ 7

Pump and running speed specification .............................................................................................................. 7

Conclusions ............................................................................................................................................................. 9

Further Work .......................................................................................................................................................... 9

Acknowledgements ................................................................................................................................................ 9

Bibliography .......................................................................................................................................................... 10

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INTRODUCTION Butterfly Space is a Community Based Organisation in

Nkhata Bay, Malawi. They seek to alleviate poverty in the

community by implementing sustainable solutions using

appropriate technology, engaging the community and

developing skills that can be transferred through to other

communities. This method of ensuring understanding of

the solutions allows them to be maintained, replicated and

adapted in the future.

Agriculture in the developing world accounts for 45% of

primary earning activity. Energy access can increase the

productivity of small agriculture business and stimulate

increases in food security, income generation, development

and poverty reduction. (Practical Action, 2012)

Although increasing access to energy is not directly stated

as one of the eight Millennium Development Goals officially

formed in 2000, it is recognised as being the driver for

many of the targets. Access to energy services is integral in

the achievement of the Millenium Development Goals and

is recognised and discussed extensively in literature (e.g

Modi, et al., 2005). Modi et al. recommend emphasis is put

on the immediate access to transistional mechanical energy

devices. For the purposes of international development,

this is a significant consideration; to recognise how the

technology and the requirements needed from it may

evolve as the users their community.

There are two distinct seasons in Malawi: the rainy season

which runs between November and April and the dry

season which between May and October (Aquastat, 2005).

It is not possible to store water for the entire dry season

and therefore Butterfly Space has identified this to be an

area in which the community needs to find a solution. An

increase in water supply during the dry season for irrigation

will allow a more sustainable source of food and income

throughout the year.

AIMS The aim of this project is to follow an engineering design

methodology in order to design a mechanism for lifting

water from Lake Malawi, to the higher ground where

smallholder farmers will use it for irrigation purposes

during the dry season, allowing a more secure food

resource and enabling development of the benefitting

communities.

The use of a design methodology will allow an

understanding of the reasons for the choice made and

therefore allow the design to be modified for differing

situations. A further aim of this project is to therefore

design a mechanism that can be adapted within a

transitioning country.

At present, the people living in these communities depend

upon rain fed agriculture growing maize once a year, but,

with the changing climate, rainfall is likely to become less

predictable and more erratic. Giving smallholder farms

access to water for irrigation throughout the year will result

in less dependency upon the vulnerable market price of

food.

It has been recognised that agriculture is the most

important sector of Malawi’s economy, contributing 37.6%

to the country’s GDP in 2003 (Aquastat, 2005). Within the

agricultural sector in Malawi there are two distinct sectors:

the low input and low productivity smallholder, and the

estate sector. The communities that will be using the water

pump being discussed in this report will be the smallholder

farmers. Smallholder farmers are those that are affected

most by the changing extreme conditions in Malawi

(ActionAid, 2006).

“Given the relatively low rainfall in parts of the country and its monomodal pattern, the potential for increased production through higher cropping intensities is severely limited without some form of irrigation. Increased irrigation, particularly in the smallholder sub-sector, is therefore essential for increased crop production.” (Aquastat, 2005)

Malawi has one of the highest intensities and rates of

energy poverty in sub-Saharan Africa with a

Multidisciplinary Energy Poverty Index (MEPI) of 0.87 in

2004 (Nussbaumer, et al., 2011). The MEPI is partially split

into two categories; the energy poverty intensity and the

ratio of energy poor. Therefore, appropriate technology

provides decentralised energy sources which help alleviate

energy poverty intensity and increase the quality of life for

the beneficiaries.

DESIGN OBJECTIVES AND SPECIFICATIONS

The following section has been compiled after conferring

with two people on the ground in Malawi, one of which

who works with the local communities in Nkhata Bay as one

of the founders of Butterfly Space.

4 Initially the design objectives shall be focussed

upon as there are few quantitative specifications

given. The objectives for the design have been

diagrammatically represented in the objective

tree shown in Figure 2.

SPECIFICATIONS

The project has been widely discussed with

volunteers at Butterfly Space and the following

have been selected as specifications:

Pump will be used primarily for

irrigation purposes.

Cost as little as possible (approximately

£100)

Operable by women and children

Accommodate for the elevation profile

shown in Figure 1 (12m vertical, 81.8

horizontal) but with changes in lake

water level it must accommodate for

(13.5m, 92m respectively)

Therefore the vertical pumping distance shall be

13.5m and the horizontal distance shall be 92m.

FIGURE 1 - ELEVATION PROFILE FOR BUTTERFLY SPACE

IMPLEMENTATION

GENERATION OF IDEAS

EXISTING TECHNOLOGIES

The following review of technologies does not

cover all water moving devices, but rather all

mechanisms which could be used or adapted as

a water lifting device for Butterfly Space’s needs.

The technologies looked into were those which

could act as both suction pumps and lift water a

significant distance, or those which could be

used in a water lifting system in other ways.

Table 1 summarises these technologies:

FIGURE 2 - OBJECTIVE TREE

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Type Pump

Suction Diaphragm Piston Treadle Centrifugal Radial Flow Centrifugal Pump Water Lifting Rope/Chain and Washer Pump Dragon Spine Pump

TABLE 1 - EXISTING RELEVANT TECHNOLOGIES

SUCTION PUMP TECHNOLOGIES Suction pump technologies would be used as part of a

suction and force system because the maximum head that

can be overcome by a suction system is theoretically

limited to 10m head of water at sea level (Awulachew, et

al., 2009). However, due to friction losses, the difficulty to

create extremely low pressures and any increase in altitude

the realistically achievable maximum head can will be

approximately 6m (Nkhata Bay is approximately 560m

above sea level).

DESIGN IDEAS

For a water lifting device the movement of water from the

pump to the tank will be more difficult than the suction

process.

The Hazen Williams (Equation 1) empirical formula is used

for the calculation of the head loss due to friction

[1]

Where K=10.67 when using metric units, L is the length of

pipe(m), Q is the flow rate (m3s

-1), D the internal diameter

(m) and C is the coefficient of friction for the pipe.

It shall be initially assumed that the pipe diameter shall be

51mm to allow maximum head and the smallest amount of

force to operate (Hofkes, 1981). This number may change

in the future sections where the design is developed.

Plastic (PVC) pipes have a coefficient of friction of

approximately 150 (Engineeringtoolbox.com, n.d.), and it

shall be assumed that there is initially a relatively low

volume output of 5m3/hour =1.389e

-3 m

3s

-1. The friction

head will therefore be approximately 1m. A further head

shall be applied to this when any bends in the pipe are

taken into account.

Assuming a very slow velocity at the outlet (therefore

negligible velocity head) the total head for a piping system

can be given as Equation 2:

[2]

Where is the friction head and is the static pressure

head. The difficulty with having a pipe so long is that with

any increase in flow rate caused by developments to the

design such as multiple operators or a solar or wind pump

will increase the friction head at a higher rate than a

shorter pipe.

From talking to people in Malawi 2 contains approximate

costs for materials.

Material/Part Cost

1”x8”x10’ wood plank ≈£1.80 6m PVC tube ≈£7.30

Bike (may not need to buy one)

≈£75

Check valve ≈£75 New centrifuge pump ≈£100

2nd

hand unusable centrifugal pump

≈£20

TABLE 2- APPROXIMATE COSTS FOR VARIOUS MATERIALS AND PARTS

IDEAS

DIAPHRAGM PUMP CONNECTED TO A BICYCLE

In order to move water the distance needed the pump will

need to be close to the water to reduce the suction head,

and will then need to push the water to the container. The

pumps mentioned in the previous sections could potentially

do this. The main issue would be the cost but if modified

effectively the benefit may be worth the increased cost.

The following designs show potential ideas.

ALTERING THE ELEVATION

Most pumps developed have been made for the movement

of water in a vertical direction. In order to achieve this for

this situation it would be necessary to extend a jetty or

supporting structure into Lake Malawi.

1. Using a jetty:

FIGURE 3 - JETTY IDEA

6 Figure 3 shows how the use of a jetty could provide an

opportunity to use existing technologies that can pump

vertically such as a rope and washer pump or a diaphragm

pump.

After the water has been lifted, gravity does the work to

transport the water through a flume to the water storage

tank. This length of flume would need to be supported

along its length. This solution could be appropriate if wood

and woodworking skills are available in abundance in the

area.

The black box represents a number of pumps that could be

used.

2. Using a cantilever:

The use of a cantilever would be possible when using a rope

and washer pump connected to a pedal powered rotor as

shown in Figure 4.

The rope and washer pump is one of the cheapest and

easiest to maintain pumps available for irrigation purposes.

This design exploits this idea and uses human pedal power

to operate a pump.

This design has the possibility to be transitional by allowing

more users when more water is needed, or by connecting a

solar powered pump to the rotor when there is enough

money in the community to do so. .

DRAGON SPINE

The dragon spine pump would allow the problems of

expensive hydraulic devices to be replaced with mechanical

energy. It has not been possible to find any examples of a

dragon spine water lifting device used over long distances.

If the water flow rate is reduced as a compromise, the

mechanism could potentially work. Problems that would

occur would be:

INTERVALS

Dividing up the journey into sections through the use of an intermediate storage tank could result in a more effective, cheap and useful water lifting system. The storage tank would not necessarily need to be the same size as the destination tank but may allow the use of the most appropriate pump. For this to be appropriate the pump would need to be portable as the pump is likely to be the most expensive part of the system.

REFURBISH AND USE CENTRIFUGAL PUMPS AND BICYCLE

As mentioned previously mentioned, the purchase of a new

centrifugal pump is not possible due to the cost of it.

However, it may be possible to use old centrifugal pumps

which have broken bearings. The power that a human is

capable of applying should be matched to the rating of the

pump and a bicycle could be used to transmit force through

the rotor, into the pump and onto the water being pumped.

Some suggestions for this have been looked into by Leary

(Leary, 2010).

The issues with this method of pumping would be the cost

of repair and the capital cost of the equipment, but when

implemented correctly by Butterfly Space, using knowledge

transfer, local skills can be developed to repair old

centrifugal pumps and could provide a means to generate

money.

SELECTING A SOLUTION Figure 5 shows the relationship between the design and

end user variables.

Wat

er

Lift

ing

De

vice

Lifting/Pumping Mechanism and

Materials Cost En

d U

ser

Operation/Build Labour/Operators

Orientation/distance pumping capabilities

Land/destination elevation

FIGURE 5 - RELATIONSHIPS BETWEEN THE DESIGN AND THE END USER

VARIABLES

These relationships can be altered through:

Intervals in pumping

Alterations to the elevation profile

Transitional designs

FIGURE 4 - CANTILEVER IDEA

7 The decision matrix in Table 5 was drawn up to choose the

most suitable design where 10 is rated highest and 0 the

lowest:

Criteria

We

igh

t

Diap

hragm

pu

mp

w

/ bicy

cle

Jetty an

d v

ertical p

um

p

Can

tilever w

ith

rop

e and

wash

er

Drago

n Sp

ine

Pu

mp

Refu

rbish

ed

centrifu

gal & b

ike

Appropriate 0.22 6 8 8 7 7

Cost 0.185 5 6 7 7 6

Safe 0.15 8 7 6 7 8

Operable 0.185 8 7 7 3 8 Reliable 0.15 5 7 6 4 7

Transitional 0.11 5 7 7 5 8

Score 6.22

5 7.03

5 6.92

5.59

7.26

TABLE 3 - DECISION MATRIX FOR IDEA SELECTION

It can be seen that the most suitable pump for the situation

will be the refurbished centrifugal pump operated by a

bicycle.

DESIGN CONSIDERATIONS The design allows Butterfly Space to implement knowledge

transfer needed before the system could be transferable,

and also impart knowledge to local people on how to

refurbish a damaged centrifugal pump. This could

potentially allow small enterprises to begin and generate

more money.

It has been shown that a 300W pump when mounted to a

bicycle can lift water the distances that are needed for this

project by Figure 6 (Leary, 2010), but it can be seen that

halving the head from 13m to 6.5m will increase the

flowrate by a factor of 4 from and therefore increase the

water lifting rate by a factor of 2, to approximately

0.6m3hour

-1

FIGURE 6 - PUMPING CAPACITY OF A 300W RATED BICYCLE OPERATED

CENTRIFUGAL PUMP (LEARY, 2010)

An important consideration in this design is the method by

which the centrifugal pump can be refurbished. The pump

itself will cost approximately £100 new and approximately

£20 second hand with unusable bearings (usually journal

bearings). This observation was provided by an engineer in

Malawi.

It is likely that the centrifugal pumps are often unusable for

other reasons. The following are common problems

encountered for small scale centrifugal pumps:

Bearings that have run dry due

Worn or brittle O-rings and clearance wear rings

A worn or melted impeller

A worn mechanical seal or thrust washer

Damaged rotor blades and casing due to erosion

Corrosion

Cavitation

The type of wear found will commonly be an indication of

the previous function of the centrifugal pump, as well as

the care taken of it. If the pump was used to pump

corrosive fluids and was commonly run dry and not flushed

out after use then it would be most likely that the pump

would be beyond the small scale refurbishment that would

be needed for this system.

The system is also transitional, allowing for the upgrading

of the pump to supply a larger amount of water when it is

desired. Secondly, it allows for the economic benefits that it

provides to be used to further improve the water supply

through the implementation of a non-human powered

pump, such as a solar powered or wind powered pump,

further increasing the amount of water pumped and the

potential amount of sellable crop. Figure 7 shows why non-

human powered devices would be preferred by comparing

to other potential prime movers:

MECHANICAL ANALYSIS AND MATERIALS

PUMP AND RUNNING SPEED SPECIFICATION

It is likely that there will not be the luxury of a wide choice

when selecting a second hand centrifugal pump in Malawi.

The selection of bicycles may also be limited but this

section of the report will demonstrate how to select a

suitable pump and bike that will suit the needs of the

community.

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FIGURE 7 - COST ATTRIBUTE OF PRIME MOVERS (FAO, 1986)

Figure 8 is a schematic of the gear train in the proposed

design demonstrated by Leary (Leary, 2010)in the design of

a similar pedal powered bicycle pump:

FIGURE 8 - THE PROPOSED GEAR TRAIN (LEARY, 2010)

(1) Front chain rings

(2) Rear Sprockets

(3) Rear Wheel

(4) Pump’s driving roller

TABLE 4 - TERMS IN FIGURE 14

The following equation can define the gear train:

Where:

= Pump operating speed (rpm)

= Pedalling cadence (rpm)

= Number of teeth on the chain ring

= The number of teeth on the sprocket

= Diameter of the wheel (mm) = Diameter of the pump roller (mm)

TABLE 5 - TERMS IN GEAR TRAIN EQUATION

It can be seen that the majority of these terms are variable

in the nature of the components that are available to the

communities in Malawi. The only value that can be

suggested is that a human’s optimum cadence for pedalling

is 80rpm (Whitt & Wilson, 1982).

It is suggested that a pump is sourced before the bicycle as

the bicycle has a more adaptable gearing system, and the

pump will also play a larger part in defining the amount of

force required to run the system. Assuming a 20% efficiency

loss and a 7m head height interval the power needed to

operate a typical pump would be 181.44W, which is

acceptable for aerobic leg power of the average woman. A

300W rated pump should be suitable.

It would be possible to vary the power required to operate

the pump by changing the gear, thus allowing less or more

powerful people operate the system. However, the

efficiency of the system will decrease as the pump moves

away from its ideal operating speed. This will reduce flow

rate but at 7m head height it will still be possible to pump

water.

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CONCLUSIONS During this design process a water lifting system has been

designed to meet strict criteria as far as possible. The

financial limitations restricted the choice of pump

significantly and it must be emphasized that in the long

term, human power is not the most economically efficient

prime mover to use. Therefore the system was designed to

be transitional where possible in order to allow

development in the future.

The pedal powered system allows for the use of leg muscles

which fatigue slower than arm muscles, and the refurbished

centrifugal pump allows the potential for small scale

enterprise in the area as well as significant skill transfer. For

this system to work however, it is necessary that there is a

pool of accessible, refurbish-able centrifugal pumps near

Butterfly Space. This needs to be confirmed, and if this is

not the case then the design could be used in other

situations worldwide.

The report has been made as explanatory as possible to

allow future interpretation and adaptation of the design

procedure for future.

FURTHER WORK This design report is not fully complete yet as for this

project to be appropriate for implementation the following

need to be completed:

Confirmation of design with Butterfly Space

FMEA analysis

Build, operation and maintenance manuals

Guide for refurbishment of small centrifugal

pumps

Prototype

ACKNOWLEDGEMENTS I would like to acknowledge the support and advice of my

supervisors, Dr Rachel Horn and Elena Rodriguez-Falcon. I

would also like to thank Josie and Jim from Butterfly Space

for the correspondence and information which is vital for a

project in this vein of international development

engineering.

All of those acknowledged here have been very busy during

my project and I appreciate the time taken to help me

complete the project.

I would also like to thank Milan Delor from EWB-Sheffield

for making the project happen in the first place.

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