What it shows
A windmill pump turns the spin of its blades into an up and down stroke that lifts water. It shows how farmers use wind to irrigate fields with no electricity.
The science
The blades turn a crank, and the crank turns circular motion into back and forth motion of a rod. The rod pushes and pulls the syringe plunger, which draws water in on one stroke and pushes it out on the other through one-way valves. Each stroke lifts a small volume of water.
Materials
Cost: under Rs 500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A multi-blade rotor from card or plastic bottle, 20 to 30 cm across
- A cardboard crank disc and a stiff wire connecting rod
- A large syringe (20 ml) with a T-connector and two small tubes
- Two one-way valves: small flaps made from balloon pieces, or aquarium air-line non-return valves
- A bottle as the water tank
- A wooden frame and a battery or USB fan
Safety
For this project: An adult must cut wire and plastic and cap the wire ends. Keep fingers away from the moving crank and blades. Never use a mains fan near water; keep the water below the fan and use a battery or USB fan.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Build the wooden frame and fix the rotor on an axle with a crank disc.
Clamp the syringe barrel to the frame in line with the rod, then fix the connecting rod from the crank pin to the plunger with a loop of wire.
Join the syringe nozzle to the T-connector, and fit a one-way valve on the inlet tube and another, pointing the other way, on the outlet tube.
Place the inlet tube in the lower water tank and the outlet over a higher container.
Turn the rotor by hand to test that the water is drawn and pushed.
Place the fan 50 cm away and count turns per minute; if the rotor stalls, oil the plunger with a drop of cooking oil and use a larger rotor.
Measure the water lifted in two minutes.
Repeat at two fan speeds and compare the water lifted.
What you should see
Each turn of the rotor lifts a small amount of water to the higher container, and faster wind gives more water per minute. A table of turns and volume shows the relation.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What does the crank do?
It changes circular motion to back and forth motion.
02Why are one-way valves needed?
They stop water flowing back.
03What fuel does the pump use?
None, only wind.
04How would a bigger pump be better?
A larger piston lifts more water per stroke.
Take it further
Change the crank radius and see how the stroke length and flow rate change.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Physics Working Models Explained
Twenty classic models, how each works and how to make it
Find out more about physics
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.