The Rope-Washer Pump - Engineers Without Borders UK

Workshop Guide:
The Rope-Washer Pump
The main purpose of this guide is to allow an EWB-UK university branch to
independently run a rope-washer pump workshop for its members. During the
workshop, members will build a full-size working model of rope-washer pump.

Contents
The Rope-Washer Pump .............................................................................. 3
Before You Begin ....................................................................................... 4
Things to Bear in Mind ............................................................................. 4
Questions to Ask ..................................................................................... 4
Do you have enough members ............................................................. 4
Do you have a suitable location ............................................................ 4
Are you going to annoy anyone ............................................................ 4
Where are you going to get your tools ................................................... 4
Materials ................................................................................................... 5
Mounting ................................................................................................ 5
Rope ...................................................................................................... 5
Plastic Bottles ......................................................................................... 5
Pipe ....................................................................................................... 5
...And Where to Get Them .......................................................................... 6
Useful Tools .............................................................................................. 6
Building the Pump ...................................................................................... 7
Mounting ................................................................................................ 7
Pipe ....................................................................................................... 7
Pipe Entrance ......................................................................................... 7
Pulley .................................................................................................... 8
Washers (Bottle Tops) ............................................................................. 8
Rope ...................................................................................................... 8
Running the Workshop ................................................................................ 9

The Rope-Washer Pump
What the method lacks in efficiency and elegance, it more than makes up
for in simplicity – and simplicity should be a highly valued attribute in any device
intended to be deployed in an LEDC environment. Small communities rarely
have the technical expertise required to repair modern equipment, let alone the
money to buy replacement parts. The result is reliance on outside help; a
situation that is simply unsustainable.
The idea of the rope-washer pump is that it is repairable by untrained
locals, using materials that are readily available. It is capable of lifting clean
groundwater up to 10m. The pump’s simple design also makes sealing the water
supply from outside contamination a realistic possibility. PumpAid have had
great success installing such sealed pumps, which are now supplying clean water
to over 1 million people in Zimbabwe and Malawi.
The final advantage of a rope-washer pump over other types is cost. As
well as allowing you to run this workshop, the low cost of these units allows
charities’ money to buy many more pumps.
The easiest way to describe the concept is via a diagram such as Figure 1.
A vertical ellipse of rope rotates in such a way that its upwards movement is
through a pipe. Washers placed at intervals along the rope are pulled upwards
through the pipe. This motion
lifts water.
The design that this
workshop is concerned with
uses plastic bottle caps and
necks as washers. Note the
orientation of the bottle tops
– this is not a bucket pump.
They do not cup the water.
Attempting this would result
in too much friction; the rope
would never move.
Figure 1 – An ideal rope-washer pump

Before You Begin
Things to Bear in Mind
The techniques described in this guide are not suitable for any long-term
pump installations, and are simply intended to demonstrate the principles behind
such pumps. This guide is not intended to be prescriptive; the materials and
bodies of water locally available will obviously vary between branches.
Questions to Ask
Do you have enough members
As a rough guide, 10 practically-minded people per pump is about the
right number for a 3-hour workshop. You should consider factors that might
affect this ideal number: things like quality of tooling and complexity of design
can make a big difference.
Do you have a suitable location
Your water source should be a minimum of 150mm deep, with a mounting
point 1-4 metres above. Again, use your judgement: a 1m lift isn’t very
impressive, while a 4m (home-made) pump might struggle. If you don’t have a
handy location, you can make do with large containers filled with water as a
source - but bear in mind that these pumps tend to throw water everywhere,
rather than neatly return it to your container. Whatever your source, a sturdy
mounting-point is a must, as such simple pumps require quite a force to get
going.
Are you going to annoy anyone
Campus security prefer some form of prior warning for projects like this;
politely request that it be allowed. These are useful people to have on your side.
If you think the building phase might get noisy, warn any potential annoyees. A
good way of avoiding any annoyance is to hold the workshop on a Sunday
afternoon. Put down plastic sheeting (bin bags); it will get messy.
Where are you going to get your tools
Have a look at the tools checklist on page Error! Bookmark not
defined.. If you already have your own tools, great. If not, can you borrow tools
from the Engineering Department Depending on how practical your regular
events are, as well as storage space, you may want to consider investing in
some tools for the society.

Materials
Mounting
How you mount your pump is entirely dependent on your location. It
should be sturdy enough to support the weight of a person, provide an upper
axle for your pump, and hold the weight of your pipe. The axle itself can be as
simple as large bolt attached horizontally. The easiest way to support your pipe
is using saddle clips.
Rope
If this were a real pump installation, you’d have to decide between cotton
and nylon roping, susceptible to water and UV decay respectively. Since it isn’t,
just use whatever’s cheap and available, though remember you might have to
practically hang on the rope to get your pump turning. Another consideration is
diameter; too thick, and you’ll have to drill large holes in your bottle-caps,
resulting in them failing.
Plastic Bottles
You’ll need to work out how many bottles you need based on the
proposed height of your pump, and a spacing of about 400mm between. At the
risk of patronisation, remember to double this height and take into account the
added rope length at the top and bottom. Sports cap bottles will make your
life a lot easier, as they’re less likely to get caught on pipe edges.
Pipe
Your only real constraint here is inside diameter: it
should be between the diameter of a plastic bottle top
and body, as shown in Figure 2. Within these constraints,
you can do whatever you like. A wider pipe means more
water, but it also means a big increase in pumping
difficulty and overall stresses. Theoretically, as pipe
radius increases, friction increases twice as fast, and the
volume (weight) of water being lifted increases as twice
the square of the radius. This could result in bottle cap
failure, or a complete seize-up.
You will likely have to cut lengths of pipe down for
transport, making the joining of lengths will be
necessary. Be aware that “push-fit” joints tend to
have a narrower inner diameter than corresponding
pipe, which can (and probably will) cause a complete
seize-up. Duct tape made a fine replacement when we hit
this problem.
Figure 2 - Pipe diameter

...And Where to Get Them
Your first port of call should be a local builders’ merchant. They will likely
stock piping, rope, any materials your mount requires, and tools. You should be
able to find suitable piping in the “wastewater” section, and they should stock
cheap, relatively strong nylon rope.
Plastic bottles aren’t difficult to come by. You could ask your members to
keep their bottles, but they’d have to do so for a good few weeks to accumulate
enough. Another good source is sports societies; they tend to go through the
sports cap bottles fairly quickly. If you’re desperate, ask University
administration where they store their collected plastic recycling.
Useful Tools
Electric drill
A decent set of drill-bits (including spade bits)
Hole-saw drill-bits
Hand saw
Hack saw
Sharp Knife
Lighter
Duct tape
Stanley knife
Epoxy Resin
Plus any tools particular to your design. How many of each tool you need
depends on how many pumps you’ll be building simultaneously.

Building the Pump
Mounting
The first thing you need to construct (or at least design) is a mounting
point. Your design should provide a strong attachment to a base, without
damaging it. If, for example, you had decided upon the location of a bridge over
water, a handrail could make a good base. A typical design is shown in Figure 3.
Figure 3 - An example hand-rail mount
A block of wood is secured using rope to prevent damage to the hand-rail, and a
large bolt provides an axle. Piping is attached using a simple saddle clip and
woodscrews.
Pipe
You should already know the distance between your mounting point and
the surface of the water; cut your pipe such that the lower end is submerged.
Remember to leave at least 150mm between the bottom of the pipe and the
bottom of your water source.
Pipe Entrance
One of the most difficult
problems to overcome during this
workshop is the tendency of the
bottle-tops to snag on the bottom
edge of the pipe, as shown in Figure
4. This will stop your pump dead. As
mentioned on Page Plastic Bottles5,
using sports cap bottles goes some
way towards solving this problem,
but you will need some kind of
attachment to prevent snags. I
suggest you leave it up to your
Figure 4 - The fatal snag

members to devise their own solutions, but
if they get stuck, the best solution we
found is shown in Figure 5. A short section
of pipe was glued perpendicular to the end
of the main pipe, to decrease the angle at
which the rope enters the bottom of the
pipe. Note that a section was cut out of the
short pipe to make a glue-able surface. The
electrical tape shown was only to hold the
joint in position while epoxy resin set.
Not shown here is the later addition
of a small panel at either end of the short
pipe, to prevent the rope from slipping
laterally. We glued the bottoms of two
extra large bottles to either end of it.
Pulley
If the bolt used as the top axle is left
unmodified, it becomes another snagging
point. Again, this is a good issue to let your
Figure 5 - Snag solution
members sort out. The best we could do
with the materials and tools available was to create a rough cylinder of wood,
and cut a groove around it for the rope to sit in.
Washers (Bottle Tops)
The bottles should be cut so that the resulting washers are as close to the
pipe’s inside diameter as possible, while being able to move freely. The best way
to quickly produce large numbers of equal-diameter bottle-tops is to cut a hole
of the right diameter in a small wooden sheet, using a hole-saw drill-bit. Then,
members can simply drop the bottle top-first into the guide and mark the correct
cutting line. Junior hacksaws make short work of plastic bottle necks.
Drill through the centre of the bottle-tops using a drill-bit size that will
allow the rope to be threaded through, but not allow knots through.
Rope
Having worked out the length of rope needed, add half a metre, and cut
using a sharp knife. Nylon rope will fray at the ends immediately, making
threading the rope through drilled bottle-caps very difficult. Use a lighter to melt
the cut ends into a solid point. Tie a knot near one end of your rope, then thread
a washer (bottom-first, to make the second knot easier) onto it, and tie another
knot close to the other side of it. The distance you should leave between
washers depends on your lift; there should be a maximum of 6 or 7 washers in
the pipe at any one time, depending on how tight a fit they are.
Put it all together, mount it, cross your fingers and give the rope a pull.

Running the Workshop
Begin the workshop with a short introduction to the pump. An important
part of the introduction is to show how useful the theory of a rope-washer pump
is. PumpAid were kind enough to post me a higher-quality DVD of a video found
on their website, which made the point quite well. Show one of the included
diagrams, and give a brief explanation of each step.
This workshop works very well if members are split into teams; not only
for each pump, but also for each component. For example, one team could be
tasked with solving the snagging issue, one team with the rope and washers,
one team with the mount, and one with the upper pulley. Encourage them to
make improvements and find their own solutions, but keep an eye out for
anything that probably won’t work.
If you want, you can add a T-piece to the top of your pipe, and have a
competition between pump teams, such as a timed filling of a large container.
Without a T-piece, water simply goes everywhere, like so:
Images and diagram may be used for educational purposes. For any
further advice or questions, feel free to contact me at ethan.fowler@gmail.com.
I should be keeping that address for a good few years to come.