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A large bellows creates a mushroom cloud at the Exploratorium in San Francisco, California.

For the writer, see Saul Bellow. For the military reservation in Hawaii, see Bellows Air Force Station.

A bellows is a device for delivering pressurized air in a controlled quantity to a controlled location. Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet. A bellows typically also has a separate inlet and valves or flaps for ensuring that air enters only through the inlet and exits only through the outlet.

The word bellows also refers to a flexible tubular or box-shaped element with adjustable length, as in photographic bellows.

Several metallurgical processes, such as iron smelting and welding, require so much heat that they could only be developed after the invention of the bellows. The bellows are used to deliver additional air to the fuel, raising the rate of combustion and therefore the heat output.

Various kinds of bellows are used in metallurgy:

• Box bellows were and are traditionally used in Asia. (1)
• Pot bellows were used in ancient Egypt. (2)
• Accordion bellows, with the characteristic pleated sides, have been used in Europe for many centuries. (3)
• Piston bellows were developed in the middle of the 18th century. (4)

The ancient Chinese engineer Du Shi once applied water-power (waterwheel) to operate bellows of a blast furnace forging cast iron. The ancient Greeks, ancient Romans, and other civilizations used bellows in bloomery furnaces producing wrought iron.

In modern industry, reciprocating bellows are usually replaced with motorized blowers.

In musical instruments, the bellows is often employed as a substitute or regulator for air pressure provided by the human lungs.

The following instruments use bellows:

• Reed organ
• Bagpipe
• Harmonium
• Portative

Cuckoo clocks also use bellows.

The bellows is the pleated expandable part that rides on an optical bench in a large- or medium format film camera. The bellows is also used in Polaroid cameras. The bellows provides a flexible dark enclosure between the film plate and the lens. In some cameras, the photographer can change the angle of the film plate with respect to the camera's center line, providing an alternate means of portraying perspective and depth.

There are 2 common kinds of camera bellows:

• bag bellows, normally used with a lens of short focal length
• accordion bellows, with a much longer range of extension.

1. http://www.anvilfire.com/FAQs/archives/g072002d.htm .
2. http://www.archaeogate.org/egittologia/article/182/8/mersa-gawasis-red-sea-egypt-unoisiao-and-bu-2003-2004-f.html .
3. [ref. needed]
4. http://www.davistownmuseum.org/TDMtoolGlossary.htm

• sylphon for uses of metal bellows in experimental physics and engineering.
• http://www.wwmag.net/blacksmith.htm for bellows used in primitive blacksmithing.
• http://www.1911encyclopedia.org/Bellows for a general discussion of bellows in metal work.

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