4/30/2012
MICHIGAN
STATE
UNIVERSITY
COLLEGE OF
ENGINEERING
PORTABLE WATER PUMP
Matthew Malek, Michael Mehall, Andrew Mozer, Daniel Pylar
Advisors: Dr. Brian S. Thompson, Simon Wachieni
ME 491
Portable Water Pump
Executive Summary
Clean and accessible water is a valuable resource that is unfortunately not widely
available to all areas globally. One such area is in Western Kenya where people often
struggle to find sources of clean water. For this reason, our contact Simon Wachieni
working at the Macheo Children’s Centre in Thika, Kenya informed us that a simple
portable water pump for use in boreholes would be incredibly helpful. It was found that
there are several possible design concept possibilities to be considered for this project.
By ranking the different concepts based on our established design parameters, it was
then possible to order each of the concepts depending on the weight of the parameters.
This was done by utilizing a decision matrix to evaluate each parameter for each
design. Using this as a guide, the advantages and disadvantages of each pump were
established and we were able to select the best possible design concepts with the
greatest potential for success. Based on this decision matrix, the two concepts chosen
for construction were the Peristaltic Pump and the Slapshot Pump. These designs were
constructed and tested on campus at Michigan State University. Theoretical calculations
were also performed on each design in order to determine which design was more
appropriate to implement based on the problem description. After comparison of the two
prototypes it was determined that the Slapshot (or Piston) Pump would be easier for
construction in Kenya and provide a more sustainable solution to the current problem
with water availability.
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Portable Water Pump
Table of Contents
Executive Summary ..................................................................................................... 1
Introduction .................................................................................................................. 4
Design Specification Decision Matrix ........................................................................... 5
Function/Performance, Energy Consumption and Mechanical Loading ....................... 6
Reliability, Maintenance, Service Life, Quality, and Operating Instructions ................. 7
Personnel, Human Factors, Health Issues, and Safety .............................................. 10
Transportation, Weight, and Size ............................................................................... 12
Delivery Date and Product Cost ................................................................................. 13
Spatial Constraints, Shelf-Life Storage, and Environmental Conditions ..................... 13
Quantity, Environmental Issues, Aesthetics, Noise Radiation, Government
Regulations, and Operating Costs ............................................................................. 14
Design Specification Conclusion ................................................................................ 15
Design Concept Decision Matrix ................................................................................ 16
Peristaltic Pump ......................................................................................................... 16
Slap Shot Pump ......................................................................................................... 21
Attachments for Slap Shot Pump ............................................................................... 26
Treadle Pump ............................................................................................................ 31
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Portable Water Pump
Rope Pump ................................................................................................................ 34
Archimedes Spiral ...................................................................................................... 39
Shadoof...................................................................................................................... 41
Design Concepts Conclusion ..................................................................................... 45
Final Design Choices ................................................................................................. 46
Construction of Prototypes ......................................................................................... 46
Piston Pump ........................................................................................................... 46
Peristaltic Pump ...................................................................................................... 53
Theoretical Comparison ............................................................................................. 59
Implementation Plan .................................................................................................. 67
Conclusion ................................................................................................................. 70
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Portable Water Pump
Introduction
Clean and accessible water is an essential ingredient for a healthy life globally,
and nowhere is this consideration more critical than the water deficient region of subSaharan Africa. Although water holes exist sporadically, gathering enough water to
quench the thirst of an entire village proves challenging, especially considering the
extremely warm climate which only causes thirst to increase. The method of collecting
water from distant water holes also necessitates transportation, often requiring women
and children to carry gallons of water over a great distance. In order to combat these
complications, a water pump will be designed in compliance with Macheo Children’s
Center to ease the process of water acquisition, and eliminate the need for transport
when the water is being extracted from locally available boreholes. Macheo Children’s
Center is the home and school of 56 children in the slums of Kenya and is run by Simon
Wachieni, a Kenya Institute of Management graduate who has worked with various child
based development organizations in Kenya. The pump’s design will require it to adhere
to the most pertinent of design specifications as determined by the team. The
specifications are determined by the native situation, providing mechanical advantage to
assist in the lifting of water and taking into account that most users are women and
children and are possibly malnourished.
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Portable Water Pump
Design Specification Decision Matrix
Decision Matrix
Parameters
Function/performance
Quality
Reliability
Maintenance
Importance
Rank
5
5
5
5
Service Life
5
Personnel
Safety
Mechanical Loading
Transportation and
Packaging
Operating Instructions
5
4
4
4
Human Factors
4
Health Issues
4
Energy Consumption
4
Weight
Environmental Conditions
3
3
Product cost
2
Size
Shelf -Life Storage
Delivery Date
Spatial Constraints
Quantity
Environmental Issues
Aesthetics
2
2
1
1
0
0
0
Noise Radiation
0
Governments Regulations
0
Operating Costs
0
4
Comments
Must pump water a minimum of ten feet
+- .010” tolerances
Must withstand pumping thirty liters of water per day
Design pump to be serviceable with
sockets/wrenches/screwdrivers
Service intervals: cleaning/tightening seals, one month
Service life: three years before maintenance costs
outweigh new device cost
Will be operated by women and children
Zero accidents per year
Target goal of five pounds-force to operate pump
Add two wheels to be rolled similar to a dolly
Provide assembly instructions with at least 10 pictures
and 2 languages
Consider energy input requirements for lifting water,
target 0.6 kilocalories per thirty liters of water to
minimize human energy waste
Add filter to bottom of pump to eliminate large
particulate matter
Must not consume more than 0.6 kilocalories when
operating for ten minutes
Forty pound target goal
Must not rust more than 5% of area of pump, must not
loosen tolerances by more than .125” compliance in
joints from dust/dirt
$60 target goal and allow for local sale and profit
opportunities
Must fit into a 3’x3’x8’ box when disassembled
One year shelf life before O-rings should be replaced
Will be completed by design day (4/27/12)
Can fit in 3’x3’x8’ box when disassembled
Will be building one prototype
Use nontoxic materials and paint
Appearance and color chosen will be neutral and
inoffensive
Operation noise level should not exceed hearing
damage threshold of 85 dB
Will comply with customs requirements for entry, only
require digging permit if new borehole is made
Energy costs should not exceed 0.6 kilocalories for ten
minute operation
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Portable Water Pump
Function/Performance, Energy Consumption and Mechanical Loading
The purpose of this mechanism is to pump water from the depths of a borehole
to the earth's surface daily. The diameter of a typical borehole is between one and two
meters, and has an overall depth of roughly thirty feet with a water level reaching as
high as ten feet below the earth's surface. The amount of water required from this pump
is thirty liters (eight gallons) per day at a flow rate of one gallon per minute. The water
retrieved will flow out into to a separate containment device to be transported. The size
of this container is user dependent, as it does not affect the nature of the water pump.
The pump will be used primarily by women and children who need assistance
pulling the weight of water from the earth. Due to this fact, the pump will require
mechanical advantage to combat the lack of strength present due to malnourishment
resulting from improper diet and disease. At a flow rate of one gallon per minute and a
lift distance of ten feet, 112 joules (0.02 kilocalories) of energy would have to be
expended to raise the said gallon. This amount of energy could be considered quite
negligible for a healthy individual, but will strain someone suffering from malnutrition.
Because their calorie intake is already limited, any way of lowering energy input is
important to assure that their bodies are able to retain the maximum amount of energy
possible to operate at the greatest potential. Therefore an input force goal of five
pounds-force is proposed and will be managed depending on how the input operation is
selected (lever, gear, etc.) to achieve this. The total energy expended to raise the water
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Portable Water Pump
for ten minutes (which at one gallon per minute would yield the required thirty liters)
shall be no more than it would take to raise it strictly manually while also taking into
account frictional loss multipliers present. This means that the user should expend a
maximum of three times the energy or 0.6 kilocalories raising the water. The
overlapping needs presented for function /performance and mechanical loading warrant
a ranking of five in the Decision Matrix, especially when considering how the quest to
answer each desired specification may impede on another.
Reliability, Maintenance, Service Life, Quality, and Operating
Instructions
Perhaps the most critical aspect that is to be considered in the design process for
the Kenyan water pump is the general quality of performance. The pump is expected to
supply about thirty liters of water a day and must stand up to that task. Because the
pump will be operated in a dry, arid environment that may be affected by treacherous
disasters ranging from widespread drought to flooding that can cause landslides,
considerations must be taken into account for these expected conditions it will
undoubtedly endure. This has prompted the team to rank the parameters of reliability,
maintenance, service life, and quality in the highest grouping of importance in the
presented Decision Matrix, receiving a full score of five, and operating instructions
closely behind with a ranking of four. In order to better understand how these five
parameters play both individual and interconnected roles in the design of the pump,
each must be separately examined.
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Portable Water Pump
To someone who has never defined an engineering problem, it may seem easy
to classify reliability, maintenance, service life, and quality as one entity. While these
parameters may be interconnected and depend on one another, it is not appropriate to
lump them into one design specification. They have different definitions and each
parameter must be addressed separately in order to design a sustainable solution.
Reliability is a term that describes the pump’s ability to maintain its intended function
while undergoing the expected thirty liters pumped per day. The pump must endure this
amount of use while not suffering problems that cannot be addressed during the regular
maintenance period. This demonstrates the connection between reliability and
maintenance, which is described in more detail later. Since the pumps will be designed
and crafted (at least initially) in the United States, expert opinion and analysis is difficult
to achieve if major issues arise and the pump breaks down and is deemed inoperable.
Answering the question of what reliable dictates is often the most challenging aspect;
however in this case there have been assumptions made and goals defined in order to
design a reliable pump. The pump will be crafted with +/- .010” tolerances and
constructed with material and configuration selections designed to endure the expected
thirty liter per day pumping quota. Although a design can sometimes be over-specified
in order to extend servicing intervals in hopes to achieve an infinitely high reliability,
maintenance of any device is inevitable and has been taken into account with the
details laid out below.
The maintenance of the pump is one of the greatest challenges in designing a
product for a remote and underprivileged area. This issue is generally amplified when
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Portable Water Pump
component specifications call for commonly used parts in the build region that are
foreign and unavailable in the destined region of operation. This is generally a result of
the consumers not having compatible tools to repair a broken product. This adversity
will likely be avoided in the case of the water pump, where our Kenyan contact has
informed the team that many tools such as sockets, wrenches and screwdrivers are
accessible to local villagers. Thus, the only hurdle in the way of maintenance in this
case is the user’s knowledge of the design since it is very difficult to repair something
which is not technically understood. In order to overcome this, detailed instruction
manuals written in at least two languages will be drawn up containing step by step
directions on proper pump use (to hopefully decrease frequency of incorrect operation
that damages the pump), and also at least ten technical component sketches showing
what mechanisms interact and their locations. By allowing for easy maintenance, the
service life of the pump will be greatly extended.
As mentioned, the pump’s service life can be maximized by implementing a
design that strongly addresses reliability and maintenance. The goal set for the pump
design is a service interval of one month, in which seals must be tightened, cleaned, or
replaced if worn to a point beyond repair. With these service intervals, it is hoped that
the pump will have a service life of up to three years before the cost of maintenance
outweighs the cost of the pump. Although these aspects have great influence on the
service life, one other often misinterpreted parameter is also vital to the success of the
pump.
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Portable Water Pump
Quality, which can often be lumped in with long term reliability, is the measure of
the tolerances and build excellence of a newly manufactured pump. The goal set for this
pump is tolerances of +/- .010”. Attention to initial quality can pay dividends in all of the
parameters previously mentioned, since a poorly constructed product will begin
suffering issues soon after its initial implementation. By designing the pump to be easy
to manufacture to meet specified dimensions and tolerances, a more sustainable pump
will result. The parameters of reliability, maintenance, service life, quality, operating
instructions are crucial in the success of the pump campaign. By remaining disciplined
and vigilant to overall pump performance and resisting the desire to cost-cut or cut
corners, the potential scope of the pump’s aid to the African people will be significantly
enlarged.
Personnel, Human Factors, Health Issues, and Safety
Personnel is an important parameter that refers to the people who will be
regularly operating the water pump. In this case our contact informed us that mostly
women and children fetch water, therefore the pump must be designed to operate under
proper strength constraints. Also to be considered is the possible malnourishment of
those operating the pump, as this is a common problem throughout Africa and could
dramatically lower the operator’s strength. Our contact informed us that this is not a
major issue where the pump will be used, so the pump may be designed around
average subject strength test studies. A degree of strength deficiency will still be
assumed however, especially in minimizing operational input to conserve scarce food
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Portable Water Pump
energy. Additionally, when the group asked Professor Reza Nassiri about the issue of
malnutrition on the strength of the Kenyan people, he described them as being
“incredibly resilient”. The one thing he did mention was that lower back problems may
be an issue that we see with working with these people. From a British study, the
average one handed pushing force of a child aged six to eight years old is fifty pounds
for males and forty pounds for females. Using two hands, the force increases to sixty
pounds for males and forty-nine pounds for females. While these values still may be a
bit high in comparison to those operating the pump, they provide a starting point for
designing the required strength input to work the pump. In addition to the use of hands
and arms to operate the pump, the possibility of using the legs, which contain some of
the strongest muscles in the body, will not be discounted as a possible way to operate
the pump.
The parameters including human factors, health issues and safety relate to the
personnel because they involve the interactions of the operator and machine. Human
factors pertaining to the pump design include the knowledge of the operator about the
pump and the input motion required to operate it. The strength and motion required
must be designed for habitual use that will not tire out the user after prolonged activity.
The planned energy that the user exerted in ten minutes should be less than 0.6
kilocalories. This issue ties into health issues and safety of the user because of the
repercussions that could occur with a non-ergonomically designed pump. Another
safety problem that may arise is the presence of dirt and other particles in the water if
there is no filtration while it is pumped and collected, which will be remedied by the
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Portable Water Pump
proposed filtration system. The design must also be child friendly and safe because
much of the time it will be operated by children. The pump will be designed to minimize
all possible accident scenarios (exposed edges, extremity damage from uncovered
moving parts, etc.), resulting in a goal of zero accidents per year. Factoring in all of
these parameters will provide a safe pump that is appropriately designed for the target
user.
Transportation, Weight, and Size
The device will be built to be transportable by local people so that the device can
be used in more than one location. The pump shall possess the ability to assist in its
transport with attachments built into the design, such as two wheels to roll it similar to a
dolly. The pump will be stored and used outside and therefore does not require
constraints on size except to restrict weight. Due to the request for the device to be
easily transported, weight is a concern to help minimize the work needed to move the
device from place to place. Because of the stressed importance on transportation
ability, transportation has received an importance ranking of four. Weight has received
an importance ranking of three due to its larger effect on transportation ability while size
has received an importance ranking of two due to its smaller effect on transportation
ability. The end goal is to have a product that weighs in at less than forty pounds and be
able to fit within a three foot by three foot by eight foot box.
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Portable Water Pump
Delivery Date and Product Cost
The parameters of delivery date and product cost are of relatively low importance
in comparison with other parameters that affect the physical design. The final pump
prototype must be completed by Design Day at the very latest but the design will go
through multiple iterations and refinements before that time. The development cost must
remain under the budget of one-thousand dollars provided, and the product cost is
planned to be less than sixty dollars, allowing low-income communities a chance to
individually or together afford one. The cost will ultimately depend on how many
changes to the design are encountered. The final design needs to be done by Design
day which happens on April 27th, 2012.
Spatial Constraints, Shelf-Life Storage, and Environmental Conditions
The pump does not have any extreme specific spatial constraints that it must fit
because it will primarily be used outdoors. It will be moved around and used at different
boreholes however, so it must be of specified size of fitting in a 3’ by 3’ by 8’ volume to
be transported and stored overnight indoors. Using it outdoors leads to the issue of
environmental conditions that may affect the use or storage of the pump. Our contact
has informed us that the conditions should not pose a great threat but should still be
taken into consideration given the nature of outdoor use. Possible sources of
environmental wear include dirt erosion on seals and temperature differences causing
thermal stress during the shift from day to night. Additionally, UV light rays may
deteriorate any plastic or rubber products that come in direct contact with sunlight. The
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Portable Water Pump
environment can also affect the shelf-life of the design because it must be able to
withstand the conditions and experience minimal wear, even if it has been sitting for a
prolonged period of time before use if it is kept outdoors.
Quantity, Environmental Issues, Aesthetics, Noise Radiation,
Government Regulations, and Operating Costs
When prioritizing the design parameters that define the project, it was found that
of a scale of zero to five, the following parameters had the lowest ranking of zero;
quantity, environmental issues, energy consumption, aesthetics, noise radiation,
government regulations, and operating costs. When speaking with our contact in Kenya,
environmental issues, aesthetics, noise radiation and government regulations were
considered a non-issue.
For environmental issues, it was determined that the surroundings that the pump
will be operated wouldn’t be adversely affected by the operation of the pump.
Aesthetics and noise radiation weren’t an issue because from what the team has been
told, there weren’t any stigmas that the pump could possess that would offend the
population and the noise of the pump wouldn’t be of a high enough magnitude to disturb
the locals, however a noise threshold of eighty-five dB will not be exceeded to prevent
hearing damage. Because the pump will be operated by human power, there is no need
for an external energy source. However, the human effort that it takes to operate the
pump has been accounted for in another design specification. From discussions with
our advisor Simon and lack of information against such on the internet, it was found that
there were not any regulations that were specific for the design of the pump itself. The
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Portable Water Pump
only regulation the Kenyan government requires is a permit to drill boreholes or dig
wells for water, not how to draw water from these wells (Dartmouth Engineering).
For operating costs, since the pump itself is human powered the only cost will be
that of calories burned in order to supply the energy. The cost of maintaining the pump
however, was accounted for in another section. Since the pump will be for a small batch
run and not be mass produced, the quantity parameter was ranked low. If the pump
were to be mass produced, there would be steps taken that would allow for greater
ease in manufacturing a large amount of them such as minimizing parts needed, cutting
out unneeded material, sending more parts pre-assembled, and implementing
resources already available in Kenya such as bicycles used as a force input method.
Design Specification Conclusion
Through the method of utilizing a decision matrix to rank design parameter
priorities, valuable information has been acquired to craft a suitable path to a successful
solution. The first step in solving any major design problem requires the definition of the
problem, since real-world engineering problems have no distinct boundary conditions.
The distinction of design specifications listed has allowed for the team to visualize the
problem from a much broader viewpoint than before, and otherwise unforeseen issues
have arisen to be dealt with. With these design specifications fresh in mind, progress
can now be made in developing appropriate solutions as the next phase of the design
process is entered. This next phase includes coming up with several design concepts
and evaluating the designs using a decision matrix.
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Portable Water Pump
Design Concept Decision Matrix
Peristaltic Slap Shot
Archimedes
Treadle
Rope Pump
Shadoof
Pump
Pump
Pump
Pump
Parameter
Weight Rank Score Rank Score Rank Score Rank Score Rank Score Rank Score
Function/Performance
5
25
5
25
5
25
5
25
2
10
5
25
Quality
4
20
3
15
3
15
2
10
2
10
4
20
Reliability
4
20
4
20
4
20
3
15
4
20
4
20
5
Maintenance
4
20
2
10
2
10
4
20
2
10
4
20
Service Life
4
20
3
15
3
15
2
10
3
15
4
20
Personnel
5
25
5
25
5
25
5
25
5
25
2
10
Safety
5
20
5
20
5
20
5
20
5
20
3
12
Mechanical Loading
5
20
4
16
4
16
3
12
1
4
1
4
Transportation
5
20
4
16
3
12
2
8
0
0
1
4
4
Operating Instructions
3
12
2
8
2
8
3
12
2
8
4
16
Human Factors
4
16
4
16
4
16
3
12
3
12
1
4
Health Issues
4
16
4
16
4
16
1
4
1
4
1
4
Energy Consumption
5
20
4
16
4
16
3
12
1
4
1
4
Weight
5
15
3
9
2
6
2
6
0
0
1
3
3
Environmental Conditions
4
12
3
9
3
9
2
6
4
12
4
12
Product Cost
3
6
2
4
2
4
2
4
0
0
4
8
2
Size
4
8
3
6
2
4
1
2
0
0
2
4
Shelf-Life Storage
4
8
4
8
4
8
3
6
4
8
5
10
Total
303
254
245
209
162
200
Peristaltic Pump
One of the pump designs that is proposed for the people of Thika is a peristaltic
pump, also known as a roller pump, or tube pump. The pump is a positive displacement
pump meaning that one side creates a larger cavity to create a vacuum and a smaller
size cavity on the discharge side. The basic idea of a peristaltic pump is that a roller
runs across a piece of tubing and creates a seal. As the roller moves across the tube, it
creates a vacuum on the inlet side initially drawing fluid into the cavity. As the first roller
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Portable Water Pump
goes further along the tube, a second roller presses against the tubing creating a seal
and pushes the fluid along until it eventually gets pushed out of the discharge side of
the pump. The inertia of the fluid allows for the pump to continually draw fluid into the
inlet side of the pump. There are many different possible configurations for the pump.
There can be rollers attached to spokes that rotate, as well as rollers that move up and
down that draw the fluid linearly. Additional ways to set up the pump are to have a 180
or 360 degree routing for a rotary pump as well as the number of rollers can change.
Each of these different styles of peristaltic pumps can be seen below.
Figure 1. 180 Degree Peristaltic Pump
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Portable Water Pump
Figure 2. 360 Degree Peristaltic Pump
There are some distinct advantages and features about a peristaltic pump that
are good for the application. Since the pump is being used in a rural area where low
maintenance is required, there are a number of things that make the peristaltic pump
well suited. The main thing about pumps that is of concern to the team is the seals. With
the peristaltic pump, the whole tube acts as a seal meaning that wear is extremely low.
One of the main reasons that peristaltic pumps are used in certain applications is that it
can pump aggressive fluids such as slurries. This is advantageous because a river
where water may be drawn from would most likely contain silt and debris. These pumps
are well suited for pumping fluids with containments. While the pump will still require a
filter to keep out large debris, particles in the water should be of little concern.
Since the pump will be used to draw water from a well, being able to draw the
water up heights of ten feet minimum is a requirement. One of the great advantages to
the peristaltic pump is that they draw a high vacuum which is required to draw water up
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Portable Water Pump
heights. There are numerous commercial available peristaltic pumps that can suck
water up to 30 feet high. The advantage to this is that the pump can stay at the top of
the well and draw in the water, rather than some other pumps that require the pump
mechanism itself to be low in the well. Another advantage to this pump for pumping
water out of a well is that the pump does not need priming. They are able to draw water
up long distances without needing the seals to be wet or primed.
One concern that is important with any style pump is wear of the tubing. The
main issue that came up is wear that may occur from ingesting debris and
contaminants. After some research, it was found that there are several different
commercially available peristaltic pumps that are able to pump abrasive slurries such as
concrete and even one that can pump a mixture that consists of 60% solids. While the
tube would most likely be made of a special proprietary material, it shows that the basic
pump design can deal with abrasive materials in the fluids. In addition to abrasive
materials getting in the tubing, the next concern is the fatigue life of the tubing.
Commercially available pumps use PVC, silicone rubber, fluoropolymer or a proprietary
material. Typically for commercial applications, the material is chosen for the type of
fluid that will be pumped through the tubing. This could be for different corrosive
chemicals that are pumped through the tubing. After some basic research into tubing
specifically made for peristaltic pumps, one was found that would last over 1000 hours
of operation on a peristaltic pump operating at 600 rpm. In addition to the high fatigue,
the tubing had high abrasion resistance and costs about $3 a foot. With the pump
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Portable Water Pump
operating for 45 minutes a day, 365 days a year, the pump will last over three and a half
years before the hose needs replacing.
As with other pumps, there is bound to be maintenance and service that will need
to be done on the pump. With the design of this pump, there are few parts that make up
the pump. The main pieces on the pump are the casing which can be made out of two
pieces, the spindle, rollers, hose and any external parts to aid in transferring power to
the pump. Additionally, the pump should not require much in the way of tools to perform
maintenance. A set of screws could remove the cover to the casing allowing access to
the hose and rollers. Along with the cover, the rollers could be attached to the spindle
with screws making a screwdriver one of the only tools that is required to perform
maintenance on the pump. The addition of external parts to aid in power transfer could
possibly increase the difficulty in performing work on the pump, but special care will be
taken to make these additions easy to maintain.
Designing the pump will require several variables to be chosen to best suit the
application. The main variables that need to be chosen are the radius that the rollers
move about, the number of rotors that are required, and the tubing material. By
changing the radius, the effort needed to draw the fluid through the pump changes. By
increasing the radius, the volume of fluid moved per rotation of the pump increases.
Additionally, increasing the radius of the pump increases the effort needed to operate
the pump since there is an increase in friction as well as the pure volume of fluid that is
being pushed. With the design specifications of effort required to operate the pump, the
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Portable Water Pump
radius of the roller spokes can be chosen as well as the diameter of the tubing used
since they both dictate the effort and displacement of the pump.
When deciding how many rollers the pump needs and whether or not to run a
360 degree pump, the desired flow rate per revolution and fatigue life needs to be taken
into account. By running a full 360 degree style pump, the pump is able to pump 50%
more volume per revolution than a 180% set up. This is advantageous in that the pump
will be able to use only one roller and flow a greater amount of fluid than a 180 degree
pump and only presses on the hose with a single roller which in turn reduces the
number of fatigue cycles that the pump sees. Additionally, the pump can be run at a
slower speed than a comparable 180 degree design. The downside to this style of pump
is that there are large amplitudes of pulsing coming from the outlet of the pump. By
using more rollers, the flow coming out of the pump is more linear and smoother.
Because of the nature of this project, the pulsing coming from the pump should not be
of great concern.
Slap Shot Pump
One of the most commonly used mechanisms for pumping water from below the earth’s
surface is that of a direct-lift, piston pump cylinder that can be operated using a variety
of input methods. This type of pump moves water using a series of two one-way check
valves; there is a piston assembly in between the valves to form suction that lifts the
water above the sealed piston and pumps it up through a spout. A sketch of the basic
pump assembly is shown in Figure 3.
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Portable Water Pump
Figure 2. Simplistic “slap-shot” Outer View
In the sketch, the pump is designed to be operated using a handle that is moved up and
down by hand/arm motion. This input is limiting however, and the design can be
changed to incorporate leg muscles to provide the continuous up and down lifting
motion. Using leg muscles allows the isolation of one of the strongest muscle groups in
the body and would no doubt be easier to operate than a hand operated pump.
The piston assembly inside the pump is the heart of this design and provides the
key to lifting water. This design has been used numerous times throughout the history of
moving water, providing a plethora of information about the construction of this piston
assembly. One extremely helpful source, Hydromissions, provided images and
construction tips on a similar pump that has been designed for use in third world
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Portable Water Pump
countries. This design features brass check valves and galvanized steel pieces
constructing the inner cylinder of the pump. The piston is made of hockey pucks that
have been milled down to a two inch diameter, hence the nickname “slap shot” pump,
but they can be made using any material as a spacer. A gasket made of thick leather
sandwiched between the spacers is then used to form a seal within the pump that will
provide the suction needed to lift water. Water travels up through the check valves of
the inner cylinder and out of the holes drilled in the steel pipe, where it sits on top of the
piston before being lifted out of the spout on the upward stroke. The outside cylinder is
made using PVC piping that the inner cylinder will pump inside of and provide the space
for water to be lifted. A picture of the required parts is shown below, with close ups of
more important parts and assemblies.
Figure 3. Internal View of "slap-shot" Components
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Portable Water Pump
This pump design offers many advantages in terms of the design specifications
outlined for the assigned task. The pump can lift water the designated ten foot minimum
from a borehole while withstanding constant pumping that provides thirty liters of water
a day. Operation of this pump also eases the mechanical load of water to an
appropriate level for the people who will be operating it, primarily undernourished
women and children. This also limits the energy consumption and effect of human
factors on the pump’s design, as it should be simple to operate even without much
background in how pumps work. The use of galvanized steel parts and the brass check
valves increases the reliability of the pump as they will not be greatly affected by dirt
and other particles that would wear down weaker materials. This can however also lead
to some disadvantages being displayed by the pump.
While this prototype has proven capable and effective at performing the assigned
task, the design has potential to be modified and the cost could be reduced
substantially. One source of cost reduction is the brass check valves. These pieces are
the most expensive part of the assembly and substituting them with PVC valves or
another possible replacement would greatly reduce the price. This is not without
sacrifice however, and it must first be ensured that the replacement part can perform
equally (or close to) as well as the brass valve. Another possible disadvantage
introduced by these parts is the increased weight and size of the pump. These
parameters are not as important as some based on the decision matrix, but are still
negatively affected by the material and must be taken into consideration.
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Portable Water Pump
The largest disadvantage to the piston operated lift pump is the difficulty of
maintenance involved with the design. The leather seals being used cannot be
guaranteed forever and will eventually have to be changed, requiring disassembly of the
inner cylinder. This could prove difficult when used in Kenya depending on available
tools and knowledge of the pump’s design. Also, if there is a problem with the filter or
check valves then it could prove very problematic. Including an instruction and
maintenance manual could alleviate some of these problems, but without background
knowledge about the pump then it may become abandoned by the people if it becomes
inoperable. These difficulties in maintenance along with the expensive and heavy metal
pieces are the leading negative factors affecting the “slap shot” pump design.
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Portable Water Pump
Attachments for Slap Shot Pump
Figure 4. Basic "Slap-Shot" Wheel Configuration
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Portable Water Pump
The basic pump design pictured above shows the force input mechanism used to
operate the stroke pump as rotational with the implementation of a wheel. This pump
utilizes the “slap shot” pump design discussed earlier and simply adds a rotational input
mechanism to operate the stroke of the pump and to lift the water out of the borehole.
The “slap shot” pump has been discussed above and has been shown to match up with
the top ranked design specifications defined in previous reports. The ease of
mechanical loading due to the input mechanism must now be examined in depth. With
the implementation of rotational input, the user can utilize the conservation of
momentum and is only required to accelerate the mechanism once instead of supplying
continuous acceleration and deceleration. It is due to the added work of this reversal of
motion that the optimal input force be continuous and rotational, thus the wheel design.
This wheel would use the technology of a slider crank mechanism to transform a
rotational input force into a transverse response force. Several different designs were
developed to show how this wheel attachment could be optimized in the final
prototyping process.
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Portable Water Pump
Figure 5. Hand Powered Wheel Attachment
The first utilization of the wheel attachment can be seen in Figure 6. This
attachment acts much like a hand crank used in boat winches. The wheel is cranked by
hand with a knob to help the user with initial acceleration of the wheel. Once a velocity
is obtained, momentum drives the pump with the user occasionally spinning the wheel
to continue the motion. This utilization of the hands and arms may be a simpler
mechanism to create and may be valid here in the United States, but most of the
population in Kenya is malnourished which complicates the design process. Due to this
malnourishment, the design must minimize mechanical loading but must also minimize
the energy consumption involved in operating the device. This minimization of energy
consumption can be optimized by providing a force input that utilizes the strongest and
largest muscles of the body. By utilizing the legs, the energy consumption is reduced
significantly. The first foot powered device can be seen below.
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Portable Water Pump
Figure 6. Foot Pedal Wheel Attachment Configuration
This device utilizes a foot pedal that supplies the motion to the wheel through a
sliding pin joint. The conservation of momentum is still in effect because once the
pumping action of the foot has given a velocity to the wheel, the wheel’s momentum will
drive the stroke of the pump and the foot pedal, requiring the user only to intermittently
pump the food pedal in order to maintain the velocity of the wheel. This foot pedal will
require an optimization between the stroke of the pump and the desired height of the
foot pedal. Due to the variation of people who could potentially be using the pump, the
height of the foot pedal could be an issue. A small child might have a hard time using
the foot pump if the pedal height is too great but if the height of the pedal is too small, it
would require many pumps and would not move the stroke the optimal distance for full
pumping power.
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Portable Water Pump
Figure 7. Bike Powered Wheel Attachment Configuration
The wheel attachment seen in Figure 8 utilizes existing resources within the
Republic of Kenya: bicycles. The attachment shown uses a no slip rod that takes the
rotational motion input by the bike tire and transverses it to the wheel used to run the
pump. This design could experience friction issues and is not necessarily the best
design to implement a bicycle attachment. The wheel attachment could be modified to
utilize a chain system that attaches to any bicycle and uses the motion of the gear train
to supply the rotation to the slider crank mechanism. Regardless, any bicycle
attachment would require the bicycles back wheel to be suspended above the ground
and would utilize the rotational motion supplied by the user to operate the tire. Using a
bicycle eliminates the need to optimize the rotational motion with the stroke of the pump
as that would be done in the design of the slider crank. Once again, the rotational
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Portable Water Pump
motion supplies mechanical advantage utilizing the conservation of momentum and
using bicycles incorporates the desired leg and foot input force. Bicycles can also be
used quite easily by both women and children and the pump will be smaller, minimizing
weight and cost because the bicycle will not be a part of the device itself. The
downsides to this mechanism are developing a device that is compatible with all
bicycles that is simple and easy to maintain. A simple extended gear train may be used
but would be hard to assemble and disassemble when changing bicycles.
Due to the “slap shot” design being one of the better concepts, it was necessary
to explore how to expand on the possible input forces utilized to operate it. Continuous
rotational motion is desired to increase mechanical advantage and utilizing the feet and
legs is important to reduce energy consumption required to operate the pump. The cost
for the “slap shot” pump is small and thus the wheel attachments can be slightly more
expensive to optimize reliability and to minimize maintenance.
Treadle Pump
The treadle pump is a design that has been in use since its development and
implementation in the 1970’s in Bangladesh as a tool to help with irrigation. The design
utilizes the strong leg muscles as a source of input, making it useful to an area where
the people are possibly malnourished and in a weakened state. A sketch of a basic
treadle pump is shown in Figure 9.
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Portable Water Pump
Figure 8. Treadle Pump
The foot pedals are each attached to a piston that moves up and down within a cylinder
to form suction. Each of the pedals is also attached to an end of a rope passing over a
pulley that is mounted on the support handle so that as one piston moves up, the other
moves down. A close up view of the interior of the piston assembly is shown below.
Figure 9. Interior View of the Piston Assembly of Treadle Pump
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As the pistons are moved up and down, the pressure differential causes water to be
lifted into the cylinders through a non-return valve at the bottom of each. The valve is
made such that water cannot go back through once it has been pumped into the
cylinder. Each of the pistons also has a non-return valve so that the water will continue
to move above the piston as it is forced downward. The water is then pumped up and
out through a spout during the upward stroke of the piston. Using the leg muscles, this
design targets one of the strongest muscle groups of the body and greatly eases the
process of lifting water.
This design has many advantages in terms of easing the mechanical loading.
The ease of motion of the pedals along with having two cylinders pumping
simultaneously allows for the required thirty liters of water per day to be pumped easily.
It also does not require as much energy input and is therefore easier to operate for the
women and children that will be collecting water. This design provides great suction
and, depending on the length of attached tubing or piping, the pump can reach the ten
foot static water head and even deeper if it becomes necessary.
When designing the treadle pump, problems may arise when faced with the issue
of sealing the interior piston assembly. A seal is required that will stand up to continuous
pumping while enduring dust and other particulate matter that may enter the assembly.
This increases the amount of maintenance required on the pump and the seals must be
checked often to ensure the pump can still perform its required function. While being
used in Kenya, those operating the pump are often without proper background on the
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Portable Water Pump
assembly and do not know how to properly clean and maintain the sealed pistons. If
these fail, then the pump is rendered useless. Another disadvantage of the treadle
pump design is the size and weight associated with the design. By nature of the pump
type, it must be built to endure the weight of a human being constantly shifting weight
and adding pressure to the pedals. This introduces stresses that must be accounted for
and requires a more robust design, naturally adding weight and cost to the pump. A
product of this increased weight is decreased mobility. The desire is for the pump to be
transportable for use with multiple boreholes, but a large, heavy treadle pump is not as
easily transportable as an alternative design.
Rope Pump
One of the simpler proposed design concepts is the Rope Pump. This pump
utilizes a circulating tether that is controlled from the ground surface via a wheel that
constrains it laterally as to only allow it to travel the designated vertical path between
the top and bottom of the borehole well. In Figure 11 it can be seen that the wheel is
supported and driven by a rod over the well opening that runs between two supports
that are positioned across from each other. This rod continues out one of the supports
where it is crafted into a handle with considerable length determined to provide
maximum mechanical advantage. As the wheel rotates, the rope that is tracked on it
traverses a circulating path between aboveground level, and the underground water
level. The rope is affixed with conical pistons, which travel the same path along with the
circulating rope. As the pistons move downward, they enter the water reservoir and
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Portable Water Pump
continue their descent until the circulating path reaches its lowest point and reverses
direction. The pistons ascend and line up with a pipe that is positioned with its end
under the water surface. Once the pistons enter the pipe, they create a tight seal with
the walls due to leather gasket material, trapping the water present inside from prior
vacuum created from the previous cylinder’s ascent. The trapped water is carried to the
surface by the rising piston, and is dumped out of a spigot immediately prior to the
upper end of the pipe. The piston exits the pipe and travels around the rotating wheel
where it begins the cycle again.
Figure 10. Rope Pump Design
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When comparing this pump’s attributes to the needs determined in the decision
matrix from the design specification report, the Rope Pump is tolerable. Its strongest
point is seen when considering the function/performance requirement of a pump that
can move water from depths of at least ten feet, and the ability to reach as far down as
thirty feet (average overall borehole depth in Thika). The pump is designed such that as
long as the pipe reaches underneath the static water head, it will be able to gather water
and bring it to the surface given sufficient input effort. The design also satisfies the need
for service intervals of one month, a time when the conical pistons would be expected to
possibly lose their sealing capability or at least require some adjustment of their
gaskets. This maintenance would also be easy to perform by making the piston-rope
assembly come together in pieces secured by simple screws and bolts that are hidden
enough to not interfere with daily operation. The pump also addresses the mechanical
loading input goal of five pounds force from the user by incorporating a variable length
turning handle as well as the capability to be mated with any type of rotation input
machine such as a bicycle, which would prove advantageous by allowing the leg
muscles to be employed.
Though the pump scores well in these highly important areas, it also fails to meet
different vital criterion that other designs do. The pump design dictates that it would be
of large physical size, with a rope long enough to reach double the distance of the static
water head, as well as an extraction cylinder that would be longer than the static head
depth which would be made of a rigid material (metal, PVC etc.) resulting in a weight
burden. Likewise, the upper half of the pump, including the supports, wheel, and drive
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Portable Water Pump
rod, would be under considerable stress as the weight of water is significant at
approximately eight pounds per gallon. This stress would either necessitate exotic
material selection, or larger physical dimensions to prevent stress induced failure. This
would be especially true for the drive rod which would experience a high bending
moment at its midpoint, certainly requiring the use of some type of metal. These
structural considerations would severely hinder efforts to minimize both cost and weight,
criterion that are hard to ignore in the impoverished and malnourished community.
This large physical size and weight would also hinder the transportability of the
pump, a specification that was deemed to be particularly crucial, since the pump is
planned to be used at various boreholes and aboveground water sources depending on
the user and water availability situation. The number of components would require a
team of movers to transport it, or even a cart or animal powered device to transport the
heavier support items and large dimension pieces such as the cylinder and rope, likely
overshooting the maximum forty pound target weight. For a community that struggles to
conserve all of the human energy they intake, senselessly requiring heavy exertion just
in transport would be unwise, as this wasted energy could be utilized to pump more
water or perform other necessary activities instead.
The nature of the design also permits less than ideal sealing, as the motion of the
pistons under the water will not be certainly known, meaning their alignment upon entry
to the pump could be misaligned causing low efficiency or even jamming. More
underwater problems exist in the movement of the pistons through the water, where
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Portable Water Pump
drag force is high, even with a relatively aerodynamic cone shape. Likewise, the
constant presence of multiple pistons in the cylinder at the same time would cause a
high amount of friction, increasing effort that would be worsened by the multiple
volumes of water which would be simultaneously lifted. An alternative design to address
the cylinder issues rids the design of the cylinder altogether, instead using cup devices
to scoop the water out of the reservoir. This device would be more preferable in regard
to reducing part count and mass; however the cups would supply more underwater
motion drag than the sleek conical pistons, and would also reduce the constraint of
unwanted lateral motion towards the bottom of the pump (rope tangles). These
disadvantages were determined to outweigh the inherent advantages causing the pump
to be a mediocre final choice.
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Portable Water Pump
Archimedes Spiral
Figure 11. Archimedes Pump Design
The Archimedes Pump design pictured above implements the use of an
Archimedes screw that is sealed against the sides of the tubing that reaches down
below the water level. This seal provides a pressure differential within the tube and
prevents the water from falling back down into the borehole. As mentioned above, the
desired method of force input required to lift the water will be rotational as to avoid a
mechanism that requires acceleration followed by deceleration and reversal of motion.
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Portable Water Pump
This reversal of motion would cause the user to input more work in order to stop the
lever, reverse the motion and accelerate the lever again. Continuous, rotational inputs
provides less work for the user by only demanding the user accelerate the force input
mechanism once and then maintain that velocity which is made easier by the first law of
thermodynamics and the conservation of momentum. The sketch above shows the
Archimedes screw being operated by a bevel gear attachment which can then be
attached to a pedal system. The sketch shows a chair with a gear train build under it but
the mechanism could easily be modified to implement a bike attachment which would
reduce weight and cost of the device by utilizing pre-existing bikes found in most
villages in Kenya. However, with the Archimedes screw, the rotational motion must be
maintained the entire time the pump is in operation and the weight and friction of the
screw itself will add severely to the mechanical loading required to operate the device.
If the continuous motion required of the operation of the Archimedes pump, then
the design moves a very large amount of water quite quickly. However to maximize the
amount of water moved by the screw it is optimal to place the screw at a 45 degree
angle which is not possible to do within the boreholes specified. Since the Archimedes
screw is stationary and attached to the mechanism, it supports most of the weight of the
water and does not require much pressure differential to lift a large amount of water.
The friction between the piping and the worm gear does provide more resistance for the
user but this is negligible compared to the input force required to turn the large, heavy
screw. The cost to develop the Archimedes screw pump is also extremely high. To
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Portable Water Pump
ensure the reliability of the pump and to reduce required maintenance, certain parts
need to be very high quality including the very large Archimedes screw and the bevel
gears. The bevel gears alone can cost anywhere between $20 and $150 depending on
the ratio between the gears, the quality, and the material of the gears. The size of the
Archimedes screw makes the cost of acquiring a pre-fabricated one out of the question.
The cost would easily be thousands of dollars to have just one of these screws made
which implies that fabrication of this screw would need to be done by the group
members and not only leaves a large margin for error but the materials needed for selffabrication would also be very high in cost. The amount of machining time would be
incredibly long and the gear would need to be cut from a solid piece of metal which is
expensive. The size and weight of the Archimedes screw would also mean that the
device not be transportable.
Benefits of the Archimedes screw design are seriously outweighed by the
inability to lift water under the specified constraints, cost, and size of the device. This
high-cost, large mechanism would also be target to the rampant theft that plagues the
Republic of Kenya. It is because of this large cost, inability to efficiently pump the water
out of the boreholes, and size that the Archimedes pump is not the optimal pump type to
be constructed for this situation.
Shadoof
A primitive but simple approach to the problem of lifting water is the Shadoof.
This pump design dates back thousands of years and has been used to gather water for
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Portable Water Pump
consumption as well as for irrigation. The basic idea behind the pump is a lever that
aids the user mostly in input technique. As seen in Figure 13, the Shadoof consists of a
bar that rotates about a pin joint at or near its midpoint, and has a counterweight on one
end and a suspended water acquisition device on the other. The bar is rotated in the
direction to move the collection device downward by pulling downward on the cable
supporting the water bucket to counter the moment supplied counterweight. The bucket
reaches the water surface, is filled, and then raised back up again manually, this time
partially aided by the counterweight moment. The theory behind the pump dictates that
the counterweight is able to balance half of the weight of the water lifted, which is the
ratio that allows for minimal energy input during each repetition. This balance ratio is
optimal because if the ratio was higher (i.e. the weight balanced the entire water
weight), the user would not have to supply any energy to lift the water on its way up, but
would need input a force equal to the entire water weight when countering the
counterweight moment and sending the bucket downward to be refilled. Therefore, it
was determined that the user would be least fatigued by performing an input that was
equal and minimal during the upward and downward motions versus exerting a large
input then no input. This follows the weight lifting concept that it is easier to perform
more repetitions of a lower weight than it is to perform less repetitions of a larger weight.
The team is conscious of the conservation of energy and that the same amount of work
would be done with either arrangement, however asymmetric ratios would prove more
exhausting and potentially detrimental to fragile malnourished bodies than the
symmetric ratio.
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Portable Water Pump
Figure 12. Shadoof Pump Basic Design
The Shadoof’s main advantages come with its simple, low part count design,
resulting in a design with long service life and intervals, easy maintenance, and strong
function/performance, all parameters that ranked highest on the design specification
decision matrix. The long service life and intervals result mostly because the Shadoof is
not technically a pump, meaning it does not have degradable seals that would need to
be replaced due to scoring from particulate matter. Therefore the only foreseen
maintenance issues would be in the pin joint that the bar pivots around, particularly
when considering a bearing, though the bearing would be self-contained and immune to
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Portable Water Pump
outside interference. This simplicity translates into maintenance so minimal that the
most catastrophic scenario possible would be replacing a snapped load bar or support,
made from readily available wood and easily installable with the basic available hand
tools. The elementary operating principles are what permit the Shadoof to be so
effective performance wise. The frequent up-down motion means water is quickly raised
and retrieved, easily eclipsing the required thirty liters per day designated by the
community especially if a large (perhaps two liter) bucket is used. These advantages
would appear to put the Shadoof pump at the top of the heap; however its main
disadvantage is so striking that it is a marginal design at best in this application.
The Shadoof fails to address the most pressing issue present in underdeveloped
Thika, poor health and malnourishment. The user is required to supply constant input
force both during water lifting and bucket refilling. Though this constant energy input is
present in some of the other designs, the method in which the energy is applied is
concerning. The user is typically standing for ideal stability, and pulls upward and
downward on the rope, mostly using the arm muscles and dangerously involving the
lower back muscles if improper techniques are involved. Some of this danger could be
avoided in the bucket raising portion of the cycle by using the quadriceps and
performing a squat-lifting motion, however instinct usually results in the back raising
method. Either way, the user is required to exert energy in a manner that essentially
promotes injury and muscle fatigue. Combined with malnourished bodies, this could
result in frequent exhaustion or even severe injury if bodily limits are exceeded due to
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Portable Water Pump
excessive loading. This hazard prompted the Shadoof to fall to the lower grouping of
preferred pumps, since even its efficient performance would be useless if it was not able
to be used.
Design Concepts Conclusion
The analysis of numerous pump design concepts has resulted in a distinct
hierarchy of potential problem solutions. By considering all possible mechanisms and
orientations appropriate for this application, it was assured that the most suitable ideas
would need to prove themselves to be chosen. The results of the decision matrix show
that the Peristaltic Pump and Slap Shot Pump warrant further investigation and
prototype construction with high scores of 303 and 254 respectively, compared with the
lower scores achieved by the Treadle Pump, Rope Pump, Archimedes Spiral, and
Shadoof which came in at 245, 209, 162, and 200 respectively. The favored pump
designs were hailed for their broad success across the most important design
specifications, barely ever dipping below a three out of five satisfaction score, while
mainly shining in the areas of function/performance and general user friendliness.
Meanwhile the less favored pumps were downgraded due to their failure to address
maintenance, user input, and transportation concerns.
A Slap Shot prototype has
already been constructed and a peristaltic will soon be manufactured to run a series of
comparison tests possibly on campus at the Red Cedar River. The successes and
failures observed during testing as well as mathematical, physical, and economic
calculations will provide insight as to which pump will be the most successful in Thika.
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Portable Water Pump
The focus on these pump designs will result in the selection of a single design to pursue
for the duration of the semester, and will ultimately be the orientation implemented in
Kenya.
Final Design Choices
Based on the results of the Design Concept Decision Matrix, the two highest
scoring designs were chosen to be prototyped and tested: the Peristaltic Pump and the
Slap Shot (piston) Pump. These two pump designs possess the most appropriate
characteristics in order to be feasibly adapted for use in Thika to solve the current
problem of obtaining water. After construction of the prototypes, they will undergo
testing and theoretical calculations will be compared in order to determine which the
best design to use moving forward is. All of the previous mentioned factors from the
design specification will be taken into account to make this decision and ensure the
design will provide a sustainable solution in the near future.
Construction of Prototypes
Piston Pump
The first design built was the Slap Shot pump, operated using a piston to create
suction within a cylinder to lift water. Before beginning the construction of this pump
however, there was much research done about the operation and construction of similar
pump concepts. It was found that this design had already been implemented in some
third world countries for use with natural water resources and experienced success in
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Portable Water Pump
doing so. Basic plans for assembly of this design were used in order to construct the
inner piston assembly of materials that may be procured in Kenya. The piston itself was
made of two pieces of rubber cut into circles drilled out so they fit around a metal
connector between two bushings. There was then a gasket made of leather sandwiched
in between the pieces of rubber that fit snugly within the cylinder to form a seal. Leather
was used because it can be obtained easily in Kenya and its ability to absorb water and
swell requires less precise cutting of the material to shape, making it easier to form with
hand tools. A picture of this inner piston assembly is shown below.
Figure 13. Inner Piston and Gasket
This piston is attached to a one way brass check valve. While brass may not be
readily available in Kenya, a few of these valves could be sent abroad in a package of
other materials in accordance with a construction kit for these types of pumps. Another
solution is to use a different kind of metal for the valve that may be easier to procure,
such as galvanized steel. This may not hold up as long as the brass but it is an
adequate replacement that would allow the device to function properly. There is another
one of these valves connected at the bottom of the pumping cylinder so two are
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Portable Water Pump
required for the construction of this pump. The upper valve attached to the piston works
to seal the cylinder and provide suction on the upstroke, while opening to allow free
water flow on the down stroke. Water travels through this valve and up into a connected
piece of metal with holes drilled into it. This allows the water to be pumped above the
piston and lifted up out of the spout of the pump.
Figure 14. Valve Assembly
The inner piston assembly must be operated within the cylinder, so a handle is
required to move the piston up and down from the top of the cylinder. This was
achieved by using a threaded rod that fits into the top bushing above the connected
metal tube with holes drilled through it. This rod was long enough to reach out of the top
of the cylinder in order to be operated. Currently, the rod has a T-shaped handle at the
top of the device for operation. But the operation could be made easier by implementing
a lever to increase the mechanical advantage, or a slider crank to change the device for
a rotational input. The current handle is shown below.
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Portable Water Pump
Figure 15. Current Handle Assembly
The outer cylinder of this pump was constructed of PVC tubing with two inches
inner diameter. This dimension is important because the gasket must seal within this
cylinder in order to create suction at the bottom of the pump. We’ve been informed that
PVC tubing is available in the area and can be found in various sizes. The bottom of this
main outer cylinder contains the second check valve inserted into a PVC bushing that
creates the foot valve assembly of the device. This bottom valve then has a threaded
PVC reducer connected to it so that a hose can be attached that will reach down to the
water level of the borehole or water resource. At the other end of the hose is a metal
filter designed to keep out any large sediment from being pumped up with the water.
This is attached with a threaded coupling containing a rubber check valve and the filter
connected with a standard hose clamp.
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Portable Water Pump
Figure 16. Foot Valve and Threaded Reducer
Figure 16. Filter Attached to End of Hose
After completing construction of this prototype, it was necessary to perform
testing of the device to ensure that it could meet the design requirements. For this the
pump was taken to a bridge at the Red Cedar River on the campus of MSU, measuring
a vertical distance of 20 feet from the water level to the pump spout. This test
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Portable Water Pump
successfully lifted water a distance of 20 feet with a volume of just under one liter per
stroke. The test was videotaped for documentation.
Figure 17. View from the Top of the Bridge
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Portable Water Pump
Figure 18. Testing of Pump (bridge view)
The performance of this pump was to be compared with the Peristaltic Pump
prototype in order to determine which design is more appropriate for implementation. As
seen in this shot of the test, the pump was strapped to the bridge using zip-ties. This is
not a plausible solution for use in Thika, so after the test a frame was built to hold the
pump with foot stands to keep the assembly stable.
The availability of materials used in construction and different sizes of tubing may
vary in Kenya, so being able to adapt the design is very important. For this reason it
may be more useful for our device to be implemented as an educational tool that
explains how these pumps could be built. Explaining the concept behind the pump
design and demonstrating how this pump works is more important than creating explicit
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Portable Water Pump
directions to replicate this exact pump. Then Macheo could use materials that are
available in their area in order to create a similar design.
Peristaltic Pump
The second prototype pump that was designed and constructed was the
peristaltic pump. The way that this pumps is works is that a tube is compressed by
moving rollers. These rollers pull the water along the tubing creating suction on one end
of the tube and force the water out on the other end. Before starting to design the pump,
research was done on different style of peristaltic pumps. There are many different
factors that affect how the pump performs. Some of the most important factors that
affect the performance of the pump are the number of rollers, how much of the tubing
wrapped around the circumference, the circumference itself, and tubing diameter. By
changing these variables, the amount of fluid moved per revolution and pumping effort
can be calculated and changed to fit different applications. By increasing the amount of
rollers in the pump make for a more consistent flow of fluid, but also increases the wear
on the tubing and the required energy to pump the fluid. By changing how much of the
tubing is wrapped around the circumference determines how much fluid is pumped per
revolution. Typically the hose only wraps around half of the circumference of the circle.
There is the possibility to go around ¾ or all the way around the circumference. By
going all the way around, a pump can operate with only one rotor which increases the
life span of the tubing since it only gets compressed once per revolution and also
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Portable Water Pump
decreases the effort to turn the pump for the same reason. Finally, changing the radius
of the rotors and the diameter of the tubing, the flow rate of the pump can be changed.
In addition to the basic setup of the pumps, research went into what type of
tubing was used. This is important for pump design since the tubing is the main
component of the pumps that wear out and degrades over time. The problem
associated with the tubing in peristaltic pumps is that they need to be able to withstand
many cycles of compression and stretching. Because of these requirements, special
tubing is made for these pumps. Typically, these pumps run neoprene, PVC, or silicone
tubing depending on the application. It was found that the ideal tubing material for our
application was neoprene. The reason why it suited our build well is that the neoprene
hose could withstand many cycles of use without deteriorating or wearing out from
sucking up impurities which are destined to be floating in a natural body of water. For
the prototype, vinyl was used since it was easier to acquire and had similar dimensions
and properties as the neoprene tubing, and can be seen below in Figure 19.
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Portable Water Pump
Figure 19. Vinyl Tubing
Once the choices were made and the pump was designed, manufacturing
started. To begin, the base was created. After discussing possible ways of
manufacturing the base with Roy and Ken from the MSU engineering shop, it was
decided that the base would be made from plastic and machined on the CNC mill,
shown in Figure 20.
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Portable Water Pump
Figure 20. Base with CNC Machine
The important thing that needed to be precise was the circumference of the circle. This
is important because any irregularities in the face would cause wear on the hosing and
prematurely wear it out. The reason it was decided to use the CNC mill was because
the different circles that were milled into the plastic could be made without rechucking
up the part, therefore keeping every operation concentric.
After the base was made, the roller plate and rollers were then created. The roller
plate is the part that the rollers mount to and rotate about. This part was made of plate
aluminum. Initially the holes were drilled where the rollers mount to and where the axles
attach to. These holes were made on a vertical, 3 axis mill. Next, a rough shape of the
circular plate was done with the band saw. To get the perfectly round shape, the part
was chucked up on a lathe where it was pinned onto the spindle by the tailstock. The
shape was then turned down with the carbide, making the piece a circle. The rollers that
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Portable Water Pump
attach to the plate were made of steel. These 3 pieces were turned down on a lathe
where the stock was turned down to the proper diameter and then faced to the correct
length. Finally, the rollers are chucked up where they are then drilled and tapped. The
entire roller assembly is shown below in Figure 21.
Figure 21. Roller Assembly
To attach the rotor plate to the base, an axle, rotor plate adaptor and bushings
needed to be made. The axle is what is connected to the pedals to transmit power to
the rotor plate. This axle is a one inch diameter steel tube. This tube is placed through
the base and rests on the bushings. The bushings are nothing more than aluminum
pieces that are lathed down and placed into the base to keep the axle from wearing
down the base. These are made in a similar fashion as the rotors except they have an
inner diameter that was made using a boring bar. The boring bar is a piece with a
carbide tip that goes into the inside of the bushing to create the inner diameter. This
specific process is displayed in Figure 22.
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Portable Water Pump
Figure 22. Bushing Machining
Finally, there is an adaptor that connects the axle to the rotor plate. This piece was
lathed out of aluminum so it can be welded to the rotor plate. Once it is welded on, the
adaptor is slid onto the axle where it needs to be positioned on the axle and holes are
drilled through both parts. Screws are then put through the holes allowing the plate and
the axle to be attached.
The last parts of the peristaltic pump manufactured were the pedal assemblies.
The pedals are composed of arms and bicycle pedals. The arms were made out of the
same HPDE plastic as the base. They were made by milling holes that allowed them to
slide onto the axle and then secured by set screws. To attach the pedals to the arms,
holes were made at the opposite ends that were tapped allowing the pedals to be
screwed onto the arms.
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Theoretical Comparison
Experimental design endeavors involve not only building testing prototypes, but
also the formulation of theoretical data based on knowledge acquired in undergraduate
engineering classes for the sake of comparison. This was no different in the process of
testing both the slapshot and the peristaltic pumps. The team decided that the relevant
performance parameters to calculate included flow rate, input force, and work & power
per specified volume pumped. The formulas used to calculate these parameters could
be considered elementary, as most of them originate in basic physics, however they are
the most applicable to the situation where more complex mathematics are unnecessary.
All values found were determined theoretically with the exception of friction.
The first pump analyzed was the slapshot pump. Before any calculations could
be performed, it was important to establish the standard physical dimensions and
specifications considered. These can be seen below in Table 1.
Table 1. Slaphot Pump Dimensions
Piston Radius (m)
Piston Stroke (m)
Piston Area (m^2)
Volume per Stroke (L)
Volume per Stroke (m^3)
0.0254
0.4572
0.00202683
0.926666638
0.000926667
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The first parameter analyzed was input force required, as it had influence on other
relevant parameters. The input force was calculated according to Newton’s 2nd Law
seen in Equation (1),
𝐹 = 𝑚𝑎
(1)
where force (F) is equal to a mass (m) multiplied by an acceleration (a) which is typically
gravity (as is the case here, denoted, g), taking the units of newtons, N In this case, the
equation was manipulated to achieve the same unit balance, utilizing the relationship
that a pressure (P) multiplied by an area (A) yields a force (N/m2*m2 = N). The
appropriate pressure and area in this situation are atmospheric pressure (approximately
101325 N/m2), and piston area (.00202683 m2) respectively. It is also important to note
that the input force changes with the desired lifting height, and that there exists a
theoretical maximum height at which a perfect vacuum pump can lift water.
The
equation used to determine this theoretical maximum is displayed below in Equation (2),
ℎ=
𝑃
𝜌𝑔
=
101325
1000∗9.81
= 10.32𝑚 = ~34 𝑓𝑡
(2)
where 𝜌 is the density of liquid water. Therefore it was concluded that the maximum lift
force would be found at a lift height of 34 ft, and the force for any other lifting height
would decrease linearly with respect to that maximum height. With this consideration in
mind, the lift height accounted for was 20 ft (height of bridge above the Red Cedar
River), and the resulting force calculation was of the form seen in Equation (3).
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Portable Water Pump
𝐹 = 𝑃𝐴 �
𝑡𝑒𝑠𝑡 𝑙𝑖𝑓𝑡 ℎ𝑒𝑖𝑔ℎ𝑡
𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑙𝑖𝑓𝑡 ℎ𝑒𝑖𝑔ℎ𝑡
20
� = 101325 ∗ 0.00203 ∗ � � = 119.4 𝑁 = 26.83 𝑙𝑏𝑓
34
(3)
26.83 lbf represents the force that is necessary to lift water a height of 20 feet
without considering friction. In order to develop a more accurate figure not only for force,
but for work and power, friction was experimentally determined since friction coefficients
and other necessary assumptions needed to calculate it would be marginally accurate
at best. A spring scale was attached to the handle and was used to move the piston up
along the cylinder. The scale read a force of 21 lbf, meaning that this was the additional
input force needed to lift the weight of the piston/handle assembly and overcome friction
between the leather gasket and the cylinder wall. This value of 21lbf was summed with
the previous 26.83 lbf found theoretically, resulting in a necessary 47.83 lbf (212.85 N)
input force to operate the pump at a height of 20 ft.
This lift force was next useful in calculating the work and power necessary to
pump 30 L of water, which would be the best way to compare the slapshot and
peristaltic pumps, since input force does not necessarily tell as much as energy
consumed does. In order to calculate the work necessary to lift 30 L of water 20 ft, it
was important to determine the equation to calculate work (W) per stroke of the piston.
The equation utilized is shown below in Equation (4), where the distance (d) is the
stroke of the piston.
𝑊𝑜𝑟𝑘 = 𝐹𝑑 = 212.85 ∗ 0.4572 = 97.32𝐽
(4)
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Portable Water Pump
Since the work of interest was for 30 L, it was necessary to determine how many
strokes are necessary to achieve this volume. By using the volume given in Table 1, it
was found that 32.4 strokes are necessary. Therefore, the total work required to pump
30 L of water 20 ft is 32.4 times the value obtained in Equation (4), or 3150.5 J (0.753
kcal). This value is actually quite acceptable, as it would take less than one food calorie
to obtain enough water to satisfy a household for a day (~8 gallons). This value was
also confirmed through a similar calculation which instead considered lifting a column of
water equal to the volume of one stroke 20 ft. Therefore, the force (F) was the weight of
.000926 m3 of water, and the distance (d) was 20 ft (6.1 m), yielding 55.58 J (an error of
1.8%). Work is a respectable indicator of total energy consumed to perform a specific
task, but power (work/time) better explains how much energy you are constantly
supplying the system per time. The relevant time in this case, is the time that it takes to
pump 30 L of water, which is dependent on the stroke volume (known), and the flow
rate (dependent on stroke rate) which was found to be 13.9 L/min at 15 strokes/min.
Therefore the time it takes to pump 30 L was found to be 129 seconds. With the time
known, the power was calculated according to Equation (5).
𝑃𝑜𝑤𝑒𝑟 =
𝑊𝑜𝑟𝑘
𝑇𝑖𝑚𝑒
=
3150.5
129
= 24.33𝑊
(5)
This means that a constant 24.33 W must be supplied in order to achieve this flow rate.
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Portable Water Pump
Next the peristaltic pump was analyzed. Again, before any calculations could be
completed the considered dimensions must be presented. These can be seen in Table
2.
Table 2. Peristaltic Pump Dimensions
Configuration
Configuration Radius (m)
Tubing Inner Diameter (m)
Tubing Area (m^2)
Total Tubing Volume (m^3)
1/2 circle
0.12703252
0.01270325
0.00012674
0.00010116
Like with the slapshot pump, input force was the first parameter necessary to calculate.
The force for this pump was calculated differently, where the mass considered was the
mass of water displacing the total tubing volume, and the acceleration gravity (g). The
mass can be obtained by multiplying the volume (V) by the density of water, resulting in
the force calculation below in Equation (6).
𝐹 = 𝑚𝑎 = 𝑉𝜌𝑔 = .0001012 ∗ 1000 ∗ 9.81 = .991𝑁 = 0.223𝑙𝑏𝑓
(6)
The theoretical required input force is much lower than with the slapshot pump, however
it can be attributed to the lower amount of water yielded per cycle. Though the
theoretical input force is quite low for this pump design, it is apparent that this pump
design should suffer from immense frictional losses. This was confirmed with the same
spring scale method used on the slapshot pump, where a required force of 59.08 N
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Portable Water Pump
(13.277lbf) was required to spin the rollers. The sum of the theoretical and experimental
frictional forces yielded a total necessary input force of 60.075 N (13.5 lbf).
By calculating the input force necessary to operate the peristaltic pump, it was
once again possible to calculate the work required to move 1 cycle’s worth of water.
This was done using the secondary confirmation method used for the slapshot pump
(force based on weight of column of water, distance being the height lifted), and is seen
below in Equation (7).
𝑊𝑜𝑟𝑘 = 𝐹𝑑 = 58.1𝐽
(7)
In order to apply this value to the 30 L comparison, the amount of cycles needed to yield
30 L had to be determined as with the slapshot pump. At an operation rate of 100 RPM,
it takes 297 rotations, or 356.4 seconds. Therefore, the total work necessary to pump 30
L of water is 297 times greater than the value obtained in Equation (7), or 17,261 J.
Therefore, with power once again defined as work per time, the constant power input
was found according to Equation (8).
𝑃𝑜𝑤𝑒𝑟 =
𝑊𝑜𝑟𝑘
𝑇𝑖𝑚𝑒
=
17261
356.4
= 48.42𝑊
(8)
With all of the relvant paramters tallied for both the slapshot and peristaltic
pumps, a tabular and graphical comparison was possible. Table 3 below shows how the
two pumps align for the parameters of input force, cost, and time, work, & power to
pump 30 L.
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Table 3. Theoretical Comparison: Slapshot vs. Peristaltic
Comparison at 20 ft Lift Height
Slapshot Peristaltic
Force (lbf)
48
13.5
Time (sec/30 L)
129
356
Work (kcal/30 L) 0.75
4.1
Power (W/30 L) 24.3
48.5
Cost ($)
91.73
63.02
Although the peristaltic pump takes much less force to operate, it actually takes much
more energy and power input to sustain the necessary flow rate, due to the small
amount of water pumped per cycle, and considerable friction. This means that someone
operating the slapshot pump would be less tired after pumping 30 L of water, even
though they have to supply more force with each cycle. The values in Table 3 were then
put into a radar graph for better relative understanding. The premise of a radar graph is
that it is best to have data points that lie closest to the center. In the case of this
comparison, the values were normalized for each parameter to whichever pump had the
highest value since some parameters were orders of magnitude higher than others. The
resulting plot is shown in Figure 23.
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Portable Water Pump
Normalized Slapshot vs. Peristaltic
Graphical Comparison
Force (lbf)
1
0.8
0.6
0.4
Cost ($)
0.2
Time (sec/30 L)
Peristaltic
0
Power (W/30 L)
Slapshot
Work (kcal/30 L)
Figure 23. Slapshot vs. Peristaltic Pump Radar Graph
The plot cements the conclusions mentioned above, where the piston pump holds
advantages in work, power, time to pump 30 L (essentially flow rate). The two
parameters where the slapshot falls short are cost, and input force. Input force has been
explained, and cost does not include machining costs, something that would drive the
price of the peristaltic pump up dramatically since its housing was crafted on a CNC
machine, and most other components were made on lathes. Therefore it was concluded
that the slapshot pump was the theoretical victor, especially since it proved to be the
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Portable Water Pump
least tiring pump to operate, something that is important to consider when designing for
operation by malnourished individuals.
Implementation Plan
The implementation and diffusion of ideas is of the utmost importance to the
success of this device and its ability to make a difference to the children of Macheo and
the surrounding villages. Humanitarian projects such as this typically fail due to a lack of
operation and maintenance knowledge of the device, leaving many projects abandoned
and unused after they malfunction. To avoid a similar fate, a simple operation and
maintenance manual will be created to send with the prototype pump to Kenya. This
manual will briefly explain the concept of the piston pump functionality, the inner
workings of the pump, their importance to its operation, the materials used, and how
they are assembled. This manual will serve as an instructional brochure that not only
informs of maintenance of the pump but more so teaches one how to construct their
own. This will be done through the use of pictures and videos of the manufacturing
processes of the individual parts of the pump and their assembly. Material suggestions
will be present for each part and possible substitute materials will be included to
increase fabrication accessibility.
The use of an operation and maintenance manual, while hopefully effective,
might not instill the desired diffusion into the Kenyan communities. Alternative
implementation devices must be employed such as convincing the leaders and figure
heads of the communities of the importance and benefits of such a project. Influence
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Portable Water Pump
can make or break almost any intent, albeit a project, an idea, a piece of legislature, or
even a relationship. A positive influence by those in power is more than necessary in
the success of this project. People like Simon Wachieni and surrounding village leaders
can provide this positive influence, helping to explain the importance and benefits of
building and utilizing these types of pumps. If leaders can be convinced of the necessity
of such devices, the likelihood of diffusion of the idea increases significantly.
The implementation plan also includes the promotion of an entrepreneurial
opportunity for small families in local villages. The pump designs were made to be
transportable for use in multiple areas and because of this; they have the ability to be
rented out for use by the owner. If a woman in a small village has the opportunity to
acquire a borehole pump, she can use it for her own family and then rent it out to her
neighbors or others in her community for a nominal fee, providing her with income and
the rest of the village with accessible borehole water. The time saved acquiring water
can then be used to pursue an education or used to find employment and bring more
income to the family, thus providing a small income and time to be used to develop a
larger income. This entrepreneurship can be utilized in more than one village by more
than one person, instilling a better quality of life for all involved.
The development of either pump by members of the community is key for such
an entrepreneurial process to succeed. Therefor materials and manufacturing
processes available in Kenya must be utilized in the fabrication of both devices. The
piston pump was made from common plastics, rubber, metal, and leather, all of which
are available in Kenya. The piston pump was also developed using only hand tools; all
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Portable Water Pump
holes and rubber seals were cut with a hand held drill. The leather was cut using
scissors and knifes and the plastic was cut to size using a hand saw and a file. The
brass check valves could be replaced with galvanized steel check valves which would
cut the cost of the device and would be easier to acquire in rural Kenya.
The peristaltic pump proves more complicated to manufacture as it was made
with exotic materials and used intense machining process. The circular pump casing
was fabricated on a CNC machine which is far from available in Kenya. Most of the
other circular metal parts were cut down on a lathe which is also unavailable. Alternative
casings such as a crude wooden casing could be fabricated but the integrity of the
circular cut would be compromised, eliminating the perfect seal needed to operate the
pump. This could be rectified by putting spring tension on the rollers to keep them flush
at all times but this adds cost and complexity to an already complex design. Another
alternate casing could be an old oil drum or a circular plastic bucket flipped on its side.
The plastic would have to be reinforced by possibly wrapping sheet metal around it or
securing it to a stand but the circular integrity would remain intact.
The steel rollers inside the peristaltic pump could be replaced with rubber wheels
from a common skateboard or pair of roller skates, both being infinitely easier to acquire
than a lathe. The pedal input could be replaced with the gear crank from any common
bicycle with the rollers attached to the largest gear itself, eliminating the need to find the
absolute center of a manufactured disk. This assembly could then be fitted inside of a
metal or plastic drum and two holes could be punched in the sides of the drum with
tubing run through it, thus effectively creating a make-shift peristaltic pump with much
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Portable Water Pump
more accessible materials and simple tools. This pump may not be extremely reliable
and may have maintenance issues due to the difficulty of finding adequate replacement
parts for those made with expensive machinery, making a simpler design more
beneficial in this type of humanitarian project.
Conclusion
The journey embarked upon by four senior mechanical engineering students to
design and manufacture a suitable water pump for Kenya proved to be challenging but
vastly beneficial. The process involved analyzing a specific problem and determining
the design specifications and boundary conditions for perhaps the first time in the
undergraduate education experience. Through these trying times in both international
and on-campus communication, a specification was finally achieved allowing for
concept generation to begin. This phase tested the resolve of the team, not permitting
settlement for an easily adaptable or comfortable design, rather encouraging
unorthodox thinking that produced some very appropriate and other not so appropriate
designs. From this diverse collection of ideas, there were two clear victors that
warranted further investigation and ultimately manufacturing. With physical prototypes
on hand, it was evident which design would be selected, confirmed by not only physical
analysis, but also relevant theoretical calculations based on knowledge acquired in the
engineering classroom. This is really the sentiment that should hold true for this entire
class experience, utilizing the theoretical education that has been pushed for the past
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Portable Water Pump
four years, and combining it with a newfound ability to make rational decisions based on
physical realities.
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