Mad about Science: Archimedes’ screw

By Brenden Bobby
Reader Columnist

Moving water somewhere you want it to go is a pain in the butt.

Projects involving moving large amounts of water generally use an electric pump, such as a well pump that many of us outside of town are accustomed to owning and operating. Vast amounts of water being moved — like through irrigation systems or hydroelectric power plants — largely rely on gravity to get water from one location to another.

But what happens if you need to move a sizable amount of water from a lower position to a higher one? A series of pumps could work, but these require an energy expenditure equal to or surpassing the mechanical work required to transport water — a heavy substance in vast quantities — from a low position to a high one.

The ancient Greeks figured out how to do it without electricity using something called Archimedes’ screw, or the Archimedean screw.

The story of this technology begins long before the birth of Archimedes of Syracuse — for whom the design is named — in the third century B.C.E. Evidence of a screw pump design has been unearthed in Egypt as long ago as 654 B.C.E. It’s also speculated that the Hanging Gardens of Babylon may have been irrigated using a form of screw pump.

There are variants of this design, with the earliest utilizing tubes wrapped helically around an inclined cylinder contained within a hollow pipe. As the screw twists, water enters the tube and is carried through by the motion of the moving helicoid (spiral screw) until it runs out of tubing and is deposited on the other end.

Another variant of this doesn’t utilize tubing, but instead has angled planes like the threads of a wood screw. Either system works, though creating a screw conveyor for your home would likely be much simpler utilizing the tubing than manufacturing big screw threads.

This process is performed in reverse to generate electrical power. Water traveling from a raised position into a lower one will turn the screw to act as a turbine, generating power. In some cases, this has been used instead of a water wheel, though a water wheel can be slightly easier to manufacture depending on the types of materials being used.

You may be wondering, if Archimedes didn’t invent it, why is it named after him?

Archimedes showcased that you don’t have to invent something to be remembered for it. You just have to make it better than anyone else.

During Archimedes’ life, Greek naval vessels were getting bigger and bigger. While the Greeks never quite mastered anything as large as a ship of the line, which would be seen from the European powers of the 17th century, they still made some impressively large vessels. The problem with big ships was that they leaked. The larger your vessel, the more vectors for failure. A ship full of water is just a reef in the making, so Archimedes was tasked with developing a mechanical solution for keeping water out of the ship.

Rather than tackling the problem at the source, Archimedes improved upon the screw conveyor. Adding more pitch or tar added weight and labor to the ship and yet more areas of potential failure — if the ship was already floating and just needed a little help, it made more sense to pump the water than stop it from entering the vessel entirely. He placed a large screw conveyor that traveled through the ship from the lowest deck to either an upper deck or off the ship entirely. Space was at a premium on Greek ships, so there was no way they could spare the space for an oxen or other beast of burden to power it — it had to be powered by a single man.

Effectively, by using screw threads instead of tubes, Archimedes was able to move a higher volume of water more consistently at the expense of requiring more materials to construct it.

This same construction is still utilized today for a host of applications. Hydroelectric dams use screw conveyor turbines to generate power. Tunnel boring machines use them to transport slurry of broken rock and mud to the back of the machine for removal and processing. It’s even used for processing wastewater, as well as moving water from the bottom of an amusement park ride to the top without using a power-hungry jet pump.

Looking to try this principle out on your own at home? You can make one using the core of a toilet paper tube, some cardstock, hot glue, and a water bottle or other container to set the screw conveyor inside. Try to use it to transfer cereal from one bowl to another on an elevated stand.

It’s a fun and challenging STEM experiment to see if you’re as smart as an engineer from the third century B.C.E. Spoiler alert: I’m definitely not, but I did manage to transfer three Cheerios with relative ease.

I’m not giving you any of my answers on this one, you’ll have to figure it out for yourself.

Stay curious, 7B.