Introduction: (Initial Observation)
Water is needed wherever people or animals live. We drink water and use it for cooking and washing. Plants need water too. Without water no plant can grow or reproduce.
The problem is that water is often underground and we need to dig a well to extract water. When a well hits underground water, the other challenge is how to bring up the water. Devices used to extract water are called pumps.
There are many different types of pumps. Different pumps use a different methods to extract and move water. In this project we will experiment building a string pump to extract water. We select string pump because it can be a manual pump and work by spinning a wheel. You can use hands, legs or the power of a windmill to spin the wheel.
Adult supervision and help is required in this project.
Information Gathering:
Find out about different types of pumps. Read books, magazines or ask professionals who might know in order to learn how different pumps work. Keep track of where you got your information from.
Following are some of the information that you may find during your research.
Technical Description
The string pump consists of a string with knots or rubber washers, whose diameters are slightly less than the diameter of the pipe, placed at intervals along it. This assembly is drawn up inside a rising pipe, and is capable of drawing relatively large volumes of water to the height of the pump. During operation, the pipe is inserted into water and the string drawn upwards through the pipe by means of a winding drum (or wheel) with a crank. Water is also drawn up and discharged at the top. The string and washers pass round the winding wheel and return to the bottom of the pipe thus completing the circuit. This design can be modified to avoid slippage of the string on the pulley by using old tire casings to make the pulley wheel. To prevent the washers getting caught, and to support the bottom of the pipe above the bottom of the well or river bed, a suitable pipe stand and string guide is necessary. Friction should be kept low by allowing leakage between the washers and the pipe stem.
This is a sample drawing for a string pump
Water can also be made to climb up a string—if the string is made to travel upward at a high speed. This can be accomplished by putting a loop of string over the rear wheel of a bicycle (with the tire removed) and putting a pulley and weight at the bottom of the loop to keep it tight. The bicycle can be pedaled fast enough to cause 6 gallons of water to “climb” up a ¼ inch string. Two strings will deliver 12 gallon per minute. The string (s) pass through a stripper box at the top to remove the water from the string and deliver it to the desiredlocation.
Notice that in this way you are not using any washer or lift disks.
String Water pump!
Made simpler every time you make one.
The String pump with plastic discs in action.
Main advantage of the string-pump is the continuous pumping action so minimal force is needed to lift water.
Most critical part of the pump is the bottom turning-point of the string. The wear can be minimized by use of a ceramic or glass cylinder (small bottle or jar) and the disks should enter the lifting tube easily by flanging (widening) the bottom end. Shown on the photos are two plastic/rubber fixtures of the PVC tubes, one already fixed into concrete. The thicker tube is used to guide the string downward, the thinner one lifts water if the disks fit neatly inside.
At the top of the lifting tube, a widening and a T-joint are required to allow the water to be delivered smoothly. The string can be driven by hand from a “wheel” which can be made from an old car tire and four pieces of wood.
The bottom of the string must go through a secure pulley inside the water. If the well is deep or the water level is not accessible, a pulley inside a heavy cement block will be used as the bottom turning point for the string.
In some other models, bottom pulley will be mounted on the bottom of the pipe.
String pump construction manual
Introduction
The string pump is a very cheap and easy to build pump which can be made of mostly waste materials. Because of its simplicity it can be built and maintained by people who aren’t technically grounded. Some practical skills are required though.
The picture on the right shows a string pump which has been made using these instructions.
Note: In the left figure a glass bottle is used as the bottom turning point.
Figure on the left shows the fundamental construction of a string pump. A string pump is made of a string with attached pistons or disks which runs through a (raising) tube. The lower side of the tube reaches the ground water and the upper side reaches above the surface. The pistons, which are attached to the string, fit in the tube with a small tolerance (0.2…0.5mm). By pulling the string through the tube a vacuum is created by the pistons so that water is taken up. A thin water film between the piston and the tube wall takes care of the greasing and also contributes to the closing between the piston and the tube. At the upper end the string runs over a wheel which pulls the string through the tube. The string runs smoothly through the tube because of a construction at the lower end of the tube.
The string pump (made of simple materials) can be used till a depth of 40 meters. The deeper the water, the smaller the diameter of the (raising) tube. Otherwise too much weight of water would have to be lifted. Especially for small tubes belonging to big pump depths it’s important that the pistons are made the right size accurately.
String pump construction design
Example of how a wooden string pump can be built. Sizes in this description are guide-lines and depend on local circumstances and available materials.
Sizes marked in italics are absolute, and are important for good operation or operation convenience.
| Composition of the rope pump.
Explanation of the letters: |
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The frame
The above figure shows how the separate parts must be put together to make a string pump.
First the posts (a), which hold the spindle (b), have to be made. The length of the posts is equal to the average elbow height (Height from ground (feet) to elbow) of the people who operate the pump plus the length which will be buried in the ground. In Europe an elbow height of 105cm is a good average. The posts have to be buried at least 1 meter in the ground. The post length in our example must be at least 205cm and is made of a beam of 5*10cm.
At the top of the posts a notch has to be made where the spindle will lay in. The notch has to be circular at the bottom, and just as deep and wide as the beam of which the spindle is made. The posts can be buried at both sides of the well, in such a way that they stand firmly.
A strip of tinplate can be folded in the notches as indicated in the right figure. The strips may not stick outside the wood, and must be sufficiently long so they can be attached to the outside of the posts.
Required tools
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Required materials
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The spindle
The length of the spindle (b), made of a beam of 5*5cm, can be adjusted so that on both sides of the posts the spindle sticks out approximately 15cm. The spindle has to be round off with the rasp where the notches in the posts touch the spindle so it can turn without too much space for motion in the notches. The length of the round off has to be a little (5mm) wider than the thickness of the posts so the spindle can turn freely.
The wheel
To finish the spindle the car-tire has to be prepared. The car-tire (t) has to be cut off on both sides at about 5 or 6 cm from the inside (where the tire laid in the wheel rim). The easiest way to do this is with a knife/bread-slicer. Make sure the knife and tire are wet so that the knife cuts easier through the tire. The two cut-out tire pieces must be lain against each other in a V-form. Where the pieces touch each other they must be attached to each other with 8 nails. Hit the 8 nails at about 8 mm of the inner edge through the tire pieces.
Now a nice circular wheel with a good V-form is made. The V-form has to be sufficiently open so the string with the pistons can lay in the V nicely.
Note that using knife to cut the tire is a dangerous task. This must not be done by young children. For your experiment you will not cut any tire. See details in the experiment section.
The spindle (continuation)
In our example we used a tire with an inner diameter of 360mm (where the tire laid in the wheel rim).
The wheel is jammed around spokes. The spokes have to be a bit bigger than the inner diameter of the tire. The spokes are made of 2 boards (c) of 10*370mm with a thickness of 18mm. These boards are nailed to the spindle (b) where the raising tube (m) comes out. Now lay the wheel (t-a) around the boards (c) and on each side shove a block (d) between the boards and the wheel so that they’re firmly attached. In our example we used 2 blocks of 50*50mm and a length of 145mm. The total diameter on the place of the blocks: (blocks) 2*145 + (board thickness) 2*18 + (spindle) 50 = 376mm. The blocks don’t have to be nailed because they’re firmly tightened by the tire.
The handle
The handle (f) is made of a beam, the beam has to have the same proportions as the beam of which the spindle (a) is made (50*50). The length of the handle must be as large as the width of the boards (e) through which it is connected to the spindle plus 20cm for the grip of the handle. In this example this is 30cm with a board breadth of 10 cm. The length for the grip has to be rounded so a synthetic tube (g) (round 40mm, length 20cm) can easily turn around it. The grip with which the spindle is turned has to be attached at a distance of 20cm from the spindle, as shown in figure. For this we use 2 boards (e) of 10*25cm with a thickness of 18mm. The spindle and grip can be attached to the boards with nails or screws.
The spindle with its rounding can now be put in the notches of the posts.
The raising tube
The length of the raising tube (m) depends on the depth of the well. The raising tube should not touch the bottom of the well, but has to hang at least 15cm (or 6″) above the bottom. A widening (o) with a length of at least 30cm has to come at the top of the raising tube which hangs underneath the wheel (t-a) but doesn’t touch the wheel.
With this data we can calculate the length of the raising tube (m). This is the length from the bottom of the well to the wheel, minus about 45cm (30+15). This is the pump height. The tube with the desired length is probably not sold in one piece but as can be seen in figure 2, several lengths of tube can be glued together using fitting sockets (n). At the bottom a funnel-shape (m-t) must be made. This can be done by gently warming the tube so that it becomes elastic and molded into the desired shape with the use of a small bottle or something similar. Make sure the funnel-shape is without dents on the inside which would prevent the pistons (v) to enter smoothly.
The inlet block
For the inlet block is needed: a small bottle (l), and a piece of wood (k) approximately as thick as the bottle (l) and with a height and length of 10*20 cm. Figure in the right (seen from the underside) shows how these items are connected together.
The bottle needs to be made heavier with wet sand and closed off with a cork. Over the length of the piece of wood a groove is made in which the raising tube (m) falls (about ¼ part of the tube diameter). At the lower side another groove has to be made so the bottle falls in it nicely. Here too, the bottle falls in it for about ¼ part. If the bottle and the end of the raising tube (with the funnel (m.t) against the bottle) are placed in the piece of wood, then it shows that the tube doesn’t lay perfectly in the groove at the place of the funnel. Remove at the place of the funnel some extra material such that the tube with the funnel falls perfectly in the groove and lays well against the bottle. This place is marked with a star (*) in the right figure.
Figure in the right shows the positions in more detail. Positions between the different parts of the inlet block. The star refers to the rubber strips which are used to tight everything together.
The upper side of the piece of wood must be rounded off so that the pistons don’t get caught behind it. The bottle and the outlet tube can be tied to the piece of wood with 2cm wide strips of inner tube (bicycle or car). Beforehand some notches must be made in the piece of wood where the inner tube can lay in. Again, this is done to prevent the scouring of the string against the strips of inner tube.
To make sure the string actually glides over the bottle and doesn’t slip of, two leading-laths (k.x) with in between a piece of PVC-tube must be attached to the inlet block where the string glides across.
Picture in the right shows a glass bottle and wood block mounted at the inlet of the pipe.
The widening and outlet
As said before the top of the tube must be a bit wider than the raising tube itself. This can be done in several ways. The easiest manner is shown in figure 2, namely with a piece of tube (o) with a larger diameter which is glued to the raising tube (m) using a reducing ring (p). Close to this glue-point a T-piece (q) must be glued in the wider tube on the place where the outlet tube (r.) can be glued on. Please look after that the inlet block is in the right position, when you glue the T-piece on the raising tube. Figure 8 shows which mistakes have to be avoided. The length of the outlet tube must be such that the water comes out of the well and a bucket must be able to be put under it. At the end of the outlet tube a bend (s) is glued to point the water stream downward instead of far away.
The widening can also be made of for example a small plastic barrel or bottle.
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| The pistons and the string Before the string pump can be completed, the string (u) with the pistons (v) must be made first. The pistons can be punched from a piece of leather or rubber with a punch. The leftovers from the piece of tire (t-b) are well suited for this. Use the remaining side because the tread consists of steel wire which can’t be punched through. A punch can be made from a piece of steel pipe with an inner diameter the same size as raising tube. By filing one side sharp the pistons can be easily punched out of the material. If the pistons aren’t the right size yet, the punch must be filed till the pistons have the right size. The right size of the pistons is when they have a tolerance of about 0.2 to 0.5mm in the raising tube. The pistons shouldn’t jam the tube in any case. A string with a diameter of approximately 4 to 5mm can best be used. The sort isn’t so important as long as it is slightly rough. Nylon is a good and cheap sort of string. The pistons must be placed 1 to 1.5 meter from each other on the string. Put a knot on both sides of the piston to fix it at it’s place. This fixation prevents that the piston can move over the string which causes extra wearing. The length of the string is about twice the length from bottom to the wheel plus 1.5 meter. Add approximately 7 cm for every knot in the string. When the string has been prepared as described it can be pulled through the raising tube. The easiest way to do this is to pull a thin piece of string with some weight underneath through the tube. The string with pistons can be tightened to the thin string and pulled through. Knot the 2 ends provisionally at the top. Don’t forget to make a large noose where the wheel is supposed to come later. |
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The raising tube support
The raising tube is suspended on top of the frame so that the lower side hangs freely inside the well. The place where the raising tube is suspended depends on the final construction. The raising tube can for example be suspended on a beam which is fastened to the edge of the well or to the posts (a) as shown in drawings. In case the latter option is used, spacing blocks (i) to keep the distance are needed between the posts and the cross-beam (h). It is very important that the beam is positioned in such a way that the string when fitted over the wheel leaves the raising tube (which is tied up to the beam) straight up. The string should not be allowed to scour the edge of the tube (o).
The assembling
Now you can lower the completely assembled tube into the well. Put the string over the wheel (t-a), and put the spindle back on the posts. The raising tube can be fastened to the beam with strips of bicycle tire. This must be done in such a manner that the space between the top of the tube and the wheel is at least 5 cm and that the string comes straight out of the tube.
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to make a working model of a string pump. Question is how can we make a pump using the material and equipment that are available to us or can be obtained easily.
To be more specific, every design element is a question. For example:
- What type of string we can use?
- What type and size of pipe we can use?
- What type and size of pulley do we need and where can we find it?
- What size of washer do we need?
Identify Variables:
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Variables in this project are often design variables. For example the diameter of pipe, size of washer, diameter of string are among variables that can be tested. However in this project we will not focus on the effect of any specific variable on the performance of the pump. Instead we attempt to come up with, and build any working model.
Hypothesis:
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
Our initial design can serve as our hypothesis.
I want to install two pulleys on a piece of board and mount a belt of string-washer on them in a way that in one side the belt passes through a pipe.
Experiment Design:
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Procedure:
In this activity we try to use rubber washers (as lift disks) on a string to move up the water in a pipe.
1. Start by mounting the washers on your string. Calculate how much string you need and cut that much of string. In doing that remember that for each washer you need to knots and each knot uses an additional one inch string. So for 20 washers or 40 nuts, you need about 4 feet extra string. For example you may start with a 12 feet string.
We want to mount washers to be about 4 inches apart.
Leave about 6 inches from one end of your string and make the first knot. Pull the string so the knot will be tight.
When the first knot is ready insert the first washer. Keep in mind the direction that you insert a beveled washer so you will do the same way for all other washers.
Make another knot after the first washer, so the washer will be secured between two knots.
Continue the same process with all 20 washers and make sure that washers are 4 inches apart and are all in the same direction. The reason that we use beveled washer and place them in the same direction is that it is easier for the beveled washers to enter the pipe from the beveled side.
Some use regular washers, instead they mount a flange at the bottom entrance of the pipe.
DO NOT tie two ends of the string at this time. String needs to pass through the pipe and pulleys and then you can tie the ends.
Connect the 18″ pipe, T connector, 5″ pipe and the angle connector as shown in the picture.
Use three 3/4″ single hole metal straps to secure the pipe on one side of the wood about 6 inches from the bottom.
Mount the 5″ bottom pulley where the string coming out of pulley can easily enter the pipe. At this time pulley will have about one inch distance from the bottom edge of the wooden board.
Mount the top pulley in the same way.
Pass the string through the pipe and two pulleys and tie the ends to form a continues loop in a way that string is well stretched.
Your string pump must be ready for test at this time. Place it in a bucket of water with a water level of one foot. In this way about 6 inches of the pipe will be in water.
Start spinning the upper pulley in a direction that moves the string upward inside the tube. As an alternative you can pull the opposite side of the string downward so the string in the pipe will move upward.
This should bring up the water and the pump should work.
| While testing see what can you do to improve the pump. Isn’t it better to use a larger upper pulley or wheel?Is it good to have a handle on the wheel to make it easier to spin?
Can you use a wooden wheel instead of metal pulley? Will you please email a picture of your pump to info@scienceproject.com. |
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Materials and Equipment:
Wooden board 1″ x 4″ x 36″- 8 feet nylon cord 1/8″ or 3mm or #4. Cotton string can be used instead.
- 20 pieces of 1/4L beveled washers (19/32″ outer diameter)
- 1.5 feet piece of 1/2″ PVC pipe
- 5″ piece of 1/2″ PVC pipe
- 1/2″ PVC T- joints
- 1/2″ PVC angle joint
- 2 nails or screws for mounting pulleys
You can use any pipe and any washer as long as washer can easily enter the pipe. Some gap between washer and pipe is ok.
- 2 pulleys
- three 3/4″ single hole metal straps and matching wood screws.
Finding pulleys can be a challenge. Hardware stores sell clothes line pulleys. We got 3 of those that you see in the picture. The white plastic one was not useable because the grove on that was too deep and narrow. The small dark blue pulley also was not a good choice because we could not disassemble it without damage. The large silver pulley was good but we had to use the help of a machinist to disassemble it.
In making a model, you can use a plastic bottle or any similar plastic container instead of bottle. You may have access to other wheels that can be used as pulleys.
As you see here we found a broken tricycle and removed one of the wheels to be used as upper pulley. Some tools and adults help is required to do this.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
- What was the result of your experiment?
- Did your pump work?
- What difficulties did you have during this experiment?
- How much water per minute can your pump transfer?
Calculations:
If you do any calculation for the length of pipe and string, write your calculations here.
Summery of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Conclusion:
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Possible Errors:
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
