If water from one section leaks into the next lower one, it will be transferred upwards by the next segment of the screw. 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 with each turn is large compared to the amount of water leaking out of each section of the screw per turn. This water is then pushed up the tube by the rotating helicoid until it pours out from the top of the tube. As the shaft turns, the bottom end scoops up a volume of water. The screw is usually turned by windmill, manual labor, cattle, or by modern means, such as a motor. The Archimedes screw consists of a screw (a helical surface surrounding a central cylindrical shaft) inside a hollow pipe. Design File:Schroef van Archimedes.jpgĪrchimedes screw as a form of art by Tony Cragg at 's-Hertogenbosch in the Netherlands This mechanism quickly replaced the ancient practice of working the pipe by treading. German engineer Konrad Kyeser equipped the Archimedes screw with a crank mechanism in his Bellifortis (1405).
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. Archimedes never claimed credit for its invention, but it was attributed to him 200 years later by Diodorus, who believed that Archimedes invented the screw pump in Egypt. This tradition may reflect only that the apparatus was unknown to the Greeks before Hellenistic times. It was described by Archimedes, on the occasion of his visit to Egypt, circa 234 BC. The screw pump was later introduced from Egypt to Greece. This is consistent with classical author Strabo, who describes the Hanging Gardens as irrigated by screws. A cuneiform inscription of Assyrian King Sennacherib (704–681 BC) has been interpreted by Stephanie Dalley to describe casting water screws in bronze some 350 years earlier. 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. A later screw pump design from Egypt had a spiral groove cut on the outside of a solid wooden cylinder and then the cylinder was covered by boards or sheets of metal closely covering the surfaces between the grooves. The Egyptian screw, used to lift water from the Nile, was composed of tubes wound round a cylinder as the entire unit rotates, water is lifted within the spiral tube to the higher elevation. The first records of a water screw, or screw pump, date back to Hellenistic Egypt before the 3rd century BC. The screw pump is the oldest positive displacement pump. History File:Irrigation Pump in Egypt - 1950's (1).tifĪ water pump in Egypt from the 1950's which uses the Archimedes' screw mechanism
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