Archimedes' screw facts for kids
Archimedes' screw is a machine. It is a type of pump used for raising water up. It is a screw inside a fairly tight-fitting cylinder. With the bottom end in water, the screw lifts water up to the top, where it pours out of a spout. The screw can be turned by hand, or by a windmill, or by an engine. The screw is often used for filling irrigation ditches.
Archimedes wrote about it when he was in Alexandria, Egypt. It is not known for certain whether he did invent it, but it is always attributed to him. The Archimedes screw is still much in use all over the world.
There is also a kind of reverse Archimedes' screw. Water poured in on top turns the screw. The turning drives an electric generator, which makes electricity. It is good for rivers with modest water drops ('low heads'). The reverse screw has the same benefits as using the screw for pumping: it can handle very dirty water and widely varying rates of flow, with high efficiency.
The screw was used predominately for the transport of water to irrigation systems and for dewatering mines or other low-lying areas. It was used for draining land that was underneath the sea in the Netherlands and other places in the creation of polders.
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. Many forms of axial flow pump basically contain 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.
An Archimedes screw was used in the successful 2001 stabilization of the Leaning Tower of Pisa. Small amounts of subsoil saturated by groundwater removed from far below the north side of the tower, and the weight of the tower itself corrected the lean. Archimedes screws are also used in chocolate fountains.
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. It is also used in a rotary-screw air compressor. On a much larger scale, Archimedes's screws of decreasing pitch are used for the compaction of waste material.
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Archimedes' screw Facts for Kids. Kiddle Encyclopedia.