Archimedes' screw

File:Archimedes-screw one-screw-threads with-ball 3D-view animated small.gif Archimedes' screw was operated by hand and could raise water efficiently File:Arkimedes skruv i Huseby.JPG An Archimedes screw in Huseby south of Växjö Sweden File:Archimedes screw.JPG Archimedes' screw File:Archscrew.jpg Roman screw used to dewater mines in Spain File:IMG 1729 Gemaal met schroef van Archimedes bij Kinderdijk.JPG Modern Archimedes screws which have replaced some of the windmills used to drain the polders at Kinderdijk in the Netherlands File:Schroef van Archimedes.jpg Archimedes' screw as a form of art by Tony Cragg at 's-Hertogenbosch in the Netherlands

The Archimedes' screw, also called the Archimedean screw or screwpump, is a machine historically used for transferring water from a low-lying body of water into irrigation ditches. The screw pump is commonly attributed to Archimedes on the occasion of his visit to Egypt, but this tradition may reflect only that the apparatus was unknown before Hellenistic times and introduced in his lifetime by unknown Greek engineers.

Design

The Archimedes' screw consists of a screw (a helical surface surrounding a central cylindrical shaft) inside a hollow pipe. The screw is turned usually by a windmill or by manual labor. As the shaft turns, the bottom end scoops up a volume of water. This water will slide up in the spiral tube, until it finally pours out from the top of the tube and feeds the irrigation systems. The screw was used mostly for draining water out of mines or other areas of low lying water.

The contact surface between the screw and the pipe does not need to be perfectly watertight, as long as the amount of water being scooped at each turn is large compared to the amount of water leaking out of each section of the screw per turn. Water leaking from one section leaks into the next lower one, so that a sort of mechanical equilibrium is achieved in use.

In some designs, the screw is fixed to the casing and they rotate together instead of the screw turning within a stationary casing. A screw could be sealed with pitch resin or some other adhesive to its casing, or cast as a single piece in bronze. Some researchers have postulated this as being the device used to irrigate the Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World. Depictions of Greek and Roman water screws show them being powered by a human treading on the outer casing to turn the entire apparatus as one piece, which would require that the casing be rigidly attached to the screw.

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The design of the everyday Greek and Roman water screw, in contrast to the heavy bronze device of Sennacherib, with its problematic drive chains, has a powerful simplicity. A double or triple helix was built of wood strips (or occasionally bronze sheeting) around a heavy wooden pole. A cylinder was built around the helices using long, narrow boards fastened to their periphery and waterproofed with pitch

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Uses

Along with transferring water to irrigation ditches, the device was also used for draining land that was underneath the sea in the Netherlands and other places in the creation of polders. A part of the sea would be enclosed and the water would be pumped out of the enclosed area, starting the process of draining the land for use in agriculture. Depending on the length and diameter of the screws, more than one machine could be used successively to lift the same water.

An Archimedes' screw was used by British soils engineer John Burland in the successful 2001 stabilization of the Leaning Tower of Pisa. Small amounts of subsoil saturated by groundwater were removed from far below the north side of the Tower, and the weight of the tower itself corrected the lean.

Archimedes' screws are used in sewage treatment plants because they cope well with varying rates of flow and with suspended solids. An auger in a snow blower or grain elevator is essentially an Archimedes' screw.

The principle is also found in pescalators, which are Archimedes screws designed to lift fish safely from ponds and transport them to another location. This technology is used primarily at fish hatcheries, where it is desirable to minimize the physical handling of fish.

History

The invention of the water screw is credited to the Greek polymath Archimedes of Syracuse in the 3rd century BC. Its tentative attribution to the 6th century BC Babylonian king Nebuchadnezzar II by the assyriologist Dalley or to pre-Hellenistic Egypt has been refuted on the grounds of "the total lack of any literary and archaeological evidence for the existence of the water-screw before ca. 250 BC". The German engineer Konrad Kyeser, in his Bellifortis (1405), equips the Archimedes screw with a crank mechanism. This mechanism soon replaced the ancient practice of working the pipe by treading.

Variants

File:Mähdrescher Schnecke.jpg

An Archimedes screw seen on a combine harvester

Main article: Screw conveyor

A screw conveyor is an Archimedes' screw contained within a tube and turned by a motor so as to deliver material from one end of the conveyor to the other. It is particularly suitable for transport of granular materials such as plastic granules used in injection molding, and cereal grains. It may also be used to transport liquids. In industrial control applications the conveyor may be used as a rotary feeder or variable rate feeder to deliver a measured rate or quantity of material into a process.

A variant of the Archimedes' screw can also be found in some injection molding machines, die casting machines and extrusion of plastics, which employ a screw of decreasing pitch to compress and melt the material. Finally, it is also used in a specific type of positive displacement air compressor: the rotary-screw air compressor. On a much larger scale, Archimedes' screws of decreasing pitch are used for the compaction of waste material.

Reverse action

If water is poured into the top of an Archimedes' screw, it will force the screw to rotate. The rotating shaft can then be used to drive an electric generator. Such an installation has the same benefits as using the screw for pumping: the ability to handle very dirty water and widely varying rates of flow at high efficiency. Settle Hydro and Torrs Hydro are two reverse screw micro hydro schemes operating in England. As a generator the screw is good at low heads, commonly found in English rivers.

See also

• Archimedes
• Machine
• Screw-propelled vehicle
• SS Archimedes – the first steamship driven by a screw propeller.
• Screw (simple machine)
• Spiral pump
• Turbine
• Vitruvius

Sources

• Oleson, John Peter (1984), Greek and Roman mechanical water-lifting devices. The History of a Technology, Dordrecht: D. Reidel, ISBN 90-277-1693-5
• Oleson, John Peter (2000), "Water-Lifting", in Wikander, Örjan, Handbook of Ancient Water Technology, Technology and Change in History, 2, Leiden, pp. 217–302 (242–251), ISBN 90-04-11123-9
• P. J. Kantert: „Manual for Archimedean Screw Pump“, Hirthammer Verlag 2008, ISBN 978-3-88721-896-6.
• P. J. Kantert: „Praxishandbuch Schneckenpumpe“, Hirthammer Verlag 2008, ISBN 978-3-88721-202-5.
• White, Jr., Lynn (1962), Medieval Technology and Social Change, Oxford: At the Clarendon Press

External links

• Technology and Culture Volume 44, Number 1, January 2003 (PDF) Dalley, Stephanie. Oleson, John Peter. "Sennacherib, Archimedes, and the Water Screw: The Context of Invention in the Ancient World"
• The Turn of the Screw: Optimal Design of an Archimedes Screw, by Chris Rorres, PhD.
• PVC archimedean screw pump, how to build a functioning Archimedes screw pump from modern materials
• Web archive backup: Plywood archimedean screw water pump, how to build a functioning Archimedes screw pump (Archived 2009-10-25)
• Manual for Screw Pumps, publisher
• "Archimedean Screw" by Sándor Kabai, Wolfram Demonstrations Project, 2007.
• "The Archimedes Screw"
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• Archimede Screw
• Archimedean Screw Generatorar:طنبور (مضخة)