Special constructions

Archimedes’ screw, also called a coclea, is an elementary device used to lift a liquid, or a sandy, gravelly, or crushed material. The machine consists of a large screw placed inside a tube. The lower part of the tube is immersed in water (or what it is to lift), after which, by placing the screw in rotation, each step picks up a certain amount of liquid, which is lifted along the spiral until it exits the upper part, where it is discharged into a reservoir. The contact between the screw and the pipe need not be watertight, as the amount of water raised at each turn is high compared to the possible leakage. In addition, water filtered from one step ends up in the lower step, which lifts it up and so on, containing the overall efficiency loss.