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Bellows are an instrument or machine that produces a current of air that may provide forced draft for a fire or sound a musical instrument. The bellows usually has an air chamber of variable volume. Air is first drawn into the chamber and then forced out as the volume is reduced.
There are four major types of bellows:
- The bag bellows is often made of a whole animal skin. The bag is shaped like a purse and opens and closes at the top during the operation.
- A drum (dish or pot) bellows consists of one or two vessels covered by a loose-fitting skin diaphragm, from which pipes lead to a nozzle. The vessels are worked alternately to expel air through the nozzle.
- The concertina bellows is of two kinds: one is an elaboration of the bag or drum bellows; the other, known as the European bellows, has two wooden heads in the shape of rectangles, circles, or pears, to which a pipe is attached. The heads are bound by a wide piece of leather that forms the air chamber.
- The pump, or piston, bellows often is a cylinder containing a single-acting piston. Another common type is the double-acting box bellows, a square-sectioned horizontal cylinder with inlet and outlet valves to control the airflow caused by a double-acting piston. Only the European and box bellows have a valve mechanism.
History of the Bellows
The bag bellows is the most ancient and widespread type, and is found today in some areas of Asia and Africa. The drum bellows appeared in Mesopotamia about 2500 B.C., and in Egypt about 1500 B.C. This type is still used in' parts of India, southeast Asia, and south and central Africa. The European bellows, derived from the bag and drum bellows, is a more recent invention, first mentioned in historical: records about the 4th century B.C. By the 12th century A.D., water-powered forms of bellows were being used in iron-smelting furnaces. The vertical pump bellows originated in Asia and is found principally in the southern and eastern regions of the continent, although it is also used in east Africa. One form of this bellows involves air chambers comprising two bamboo cylinders with plungers wrapped in down; the down acts as a valve. The box bellows was known in China from the 4th century B.C.
The bellows supplemented and often superseded blowpipes as a source of draft for fires used to produce metal from ore. The early use of the bellows made possible efficient iron smelting and was essential to the production of cast iron. Forms of bellows have also been used in mining shafts to increase the oxygen supply of miners.
However the most important regular use of bellows, other than for metallurgy, is in musical instruments. It is thought that bellows for this purpose first appeared in the 4th century A.D., for use in the Byzantine organ, which succeeded the Greek water organ. The bellows in the Byzantine organ was probably of the drum or European type. Later European organs employed the European bellows exclusively.
Bagpipes, known from the 1st century A.D., are usually inflated by human breath, and the bag is therefore considered a wind reservoir and not a bellows. Some bagpipes, however, such as the 17th-century French musette, employ a type of European bellows to create the sound. The accordion, a 19th-century invention, uses the concertina bellows. Indigenous New World civilizations were not familiar with the bellows for any purpose. Their peoples probably relied on blowpipes, fans, and winds for fire drafts. The gold, silver, copper, and bronze with which they worked had low melting points and could be worked without the intense heat created by use of a bellows.