Chain pump

The chain pump is type of a water pump in which several circular discs are positioned on an endless chain. One part of the chain dips into the water, and the chain runs through a tube, slightly bigger than the diameter of the discs. As the chain is drawn up the tube, water becomes trapped between the discs and is lifted to and discharged at the top. Chain pumps were used for centuries in the ancient Middle East, Europe, and China. The earliest evidence for this device is in a Babylonian text from about 700 B.C. They were commonly powered by humans or animals. The device then appeared in ancient Egypt from about 200 B.C., featuring a pair of gear-wheels. A version of the chain pump was used in Ancient Greek and Roman, sometimes with pots, or scoops fixed to the chain, which, as they passed over the top pulley, tipped the water out; a 2nd century example is preserved in London. Philo of Byzantium wrote of such a device in the 2nd century B.C.; the historian Vitruvius mentioned them around 30 B.C. Fragments of the cogs, crank, and discs, of a Bilge pump, from a 1st Century Roman barge, were unearthed at Lake Nemi. Chain pumps were used in European mines during the Renaissance; mineralogist Georg Agricola illustrated them in his De re metallica (1556). They were used in dockyards, and several formed part of the Portsmouth Block Mills complex. Chain pumps were commonly used on naval vessels of the time to pump the bilges, and examples are known in the nineteenth century for low-lift irrigation. Chain pumps were also used in ancient China from at least the 1st century A.D. In China, they were also called dragon backbones. One of the earliest accounts was a description by the Han Dynasty philosopher Wang Chong (A.D. 27–97) around A.D. 80. Unlike those found in the West, chain pumps in China resembled the square-pallet type instead of the pear-shaped bucket. Illustrations of such Chinese chain pumps show them drawing water up a slanted channel.