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A bellows (AKA Bagpipe) 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.


Several processes, such as metallurgical 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)
  • Tatara foot bellows from Japan.
  • 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 in Europe (4). However, the double action piston bellows were utilised by the Han rulers in ancient China as early as the 3rd century BCE (5).
  • Metal bellows were made to absorb axial movement in a dynamic condition.Often referred to as Axial Dynamics bellow types (6)

The ancient Chinese craftsman 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. Bellows are also used to send pressurized air in a controlled manner in a fired heater.

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

Double acting piston bellows

Double acting piston bellows are a type of bellows, used by blacksmiths and smelters, with the property that air is blown out on both strokes of the handle (in contrast to more common bellows that blow air when the stroke is in one direction and refill the bellow in the other direction). These bellows blew a stronger and more constant blast than typical bellows.

A piston is enclosed in a rectangular box with a handle coming out one side. The piston edges are covered with feathers, fur, or soft paper to ensure that it is airtight and lubricated. As the piston is pulled, air from one side enters and flows through the nozzle and as it is pushed air enters from the opposite side and flows through the same nozzle.

Further applications

  • Bellows are widely used in industrial and mechanical applications such as rod boots, machinery way covers, lift covers and rail covers.
  • Bellows tubing, a type of lightweight, flexible, extensible tubing may be used for delivery of gas or air at near-ambient pressure, as in early aqua-lung designs.
  • Cuckoo clocks use bellows to blow air through their gedackt (pipes) and imitate the call of the Common Cuckoo bird.
  • Folding cameras, such as early Polaroid models and some early Kodak Retina and Retinette cameras, used bellows to exclude light while allowing the lens to be moved relative to the film plane for focusing.
  • Musical instruments may employ bellows as a substitute or regulator for air pressure provided by the human lungs:
  • Piping expansion joint: In this application, bellows are formed in series to absorb thermal movement and vibration in piping systems that transport high temperature media such as exhaust gases or steam. (8)

Image:SEALED-BELLOW.JPG|Urethane bellowsImage:Blowing_Smoke.jpg|A large bellows creates a mushroom cloud at the Exploratoriummarker in San Francisco, Californiamarker.

See also

  • sylphon for uses of metal bellows in experimental physics and engineering.




  • .
  • Gernet, Jacques, trans. by J. R. Foster (1972): A History of Chinese Civilization, Cambridge University Press.
  • (How a Bellows Works)

External links

  • for bellows used in primitive blacksmithing.
  • for a general discussion of bellows in metal work.

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