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 may have a separate air inlet and check valve
Check valve
A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid to flow through it in only one direction....

s or flaps to ensure that air enters only through the inlet and exits only through the outlet; the nozzle may be very close to a fire and dangerously hot air.


Several processes, such as metallurgical iron smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...

 and welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

, 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
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...

  • Box bellows were and are traditionally used in Asia. (1)
  • Pot bellows were used in ancient Egypt. (2)
  • Tatara
    Tatara (furnace)
    The is the traditional Japanese furnace used for smelting iron and steel.The word originally meant just foot bellows, but its use was later extended to the whole furnace...

     foot bellows from Japan.
  • Accordion
    The accordion is a box-shaped musical instrument of the bellows-driven free-reed aerophone family, sometimes referred to as a squeezebox. A person who plays the accordion is called an accordionist....

     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
    Metal bellows
    Metal bellows are elastic vessels that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape .Bellows technology of the 20th and 21st century is centered on metal...

     were made to absorb axial movement in a dynamic condition. Often referred to as Axial Dynamics bellow types (6)

The Han Dynasty
Han Dynasty
The Han Dynasty was the second imperial dynasty of China, preceded by the Qin Dynasty and succeeded by the Three Kingdoms . It was founded by the rebel leader Liu Bang, known posthumously as Emperor Gaozu of Han. It was briefly interrupted by the Xin Dynasty of the former regent Wang Mang...

 Chinese mechanical engineer Du Shi
Du Shi
Du Shi was a Chinese governmental Prefect of Nanyang in 31 AD and a mechanical engineer of the Eastern Han Dynasty in ancient China. Du Shi is credited with being the first to apply hydraulic power to operate bellows in metallurgy...

 (d. 38) is credited with being the first to apply hydraulic power, through a waterwheel, to operate bellows in metallurgy. His invention was used to operate piston bellows of blast furnaces in order to forge cast iron
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...

. The ancient Greeks, ancient Romans, and other civilizations used bellows in bloomery
A bloomery is a type of furnace once widely used for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. A bloomery's product is a porous mass of iron and slag called a bloom. This mix of slag and iron in the bloom is termed sponge iron, which...

 furnaces producing wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...

. 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.

Two-chambered forge bellows

The most common type of bellows used by blacksmiths for delivering air to the forge. Preferred for their near constant stream of air, they are typically constructed similarly to fireplace bellows, but made with a two-section accordion, allowing for two chambers separated by a central divider. They are mounted by the middle paddle, and air is drawn in through the bottom chamber, then forced into the upper, which has a constant rate of exhaust due to a weight or spring pushing down.

Double-acting piston bellows

Double-acting piston bellows are a type of bellows used by blacksmith
A blacksmith is a person who creates objects from wrought iron or steel by forging the metal; that is, by using tools to hammer, bend, and cut...

s and smelters to increase the air flow going into the forge, with the property that air is blown out on both strokes of the handle (in contrast to simpler and more common bellows that blow air when the stroke is in one direction and refill the bellows in the other direction). These bellows blow a more constant, and thus stronger, blast than simple bellows. Such bellows existed in China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 atleast since the 5th century BCE, when it was invented, and had reached Europe by the 16th century.

A piston is enclosed in a rectangular box with a handle coming out one side. The piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

 edges are covered with feathers, fur, or soft paper to ensure that it is airtight
Seal (mechanical)
A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage , containing pressure, or excluding contamination...

 and lubricated
Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. The interposed...

. 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 are widely used on articulated buses and trams, to cover the joint where the vehicle bends.
  • Bellows are an essential part of anesthesia machines.
  • 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
    Aqua-Lung was the original name of the first open-circuit free-swimming underwater breathing set in reaching worldwide popularity and commercial success...

  • Cuckoo clock
    Cuckoo clock
    A cuckoo clock is a clock, typically pendulum-regulated, that strikes the hours with a sound like a common cuckoo's call and typically has a mechanical cuckoo that emerges with each note...

    s use bellows to blow air through their gedackt
    Gedackt is the name of a family of stops in pipe organ building. They are one of the most common types of organ flue pipe. The name is a German word, meaning "capped" or "covered".- History :...

     (pipes) and imitate the call of the Common Cuckoo bird.
  • Folding camera
    A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...

    s, such as early Polaroid
    Instant camera
    The instant camera is a type of camera that generates a developed film image. The most popular types to use self-developing film were formerly made by Polaroid Corporation....

     models and some early Kodak Retina
    Kodak Retina
    Retina was the name of a long-running series of German-built Kodak cameras. Retinas were manufactured in Stuttgart by Nagel Camerawerk, which Kodak had acquired in 1931, and sold under the Kodak nameplate. Retinas were noted for their compact size, quality, and low cost compared to their...

     and Retinette
    Kodak Retinette
    Kodak Retinette is the name of a classic series of cameras manufactured by the Eastman Kodak company. They were introduced in 1939 as a less expensive alternative to the Kodak Retina series. The first models were of the folding type using bellows and their lenses had three elements as compared to...

     cameras, used bellows to exclude light while allowing the lens to be moved relative to the film plane for focusing. View cameras
    View camera
    The view camera is a type of camera first developed in the era of the Daguerreotype and still in use today, though with many refinements. It comprises a flexible bellows which forms a light-tight seal between two adjustable standards, one of which holds a lens, and the other a viewfinder or a...

     also employ bellows to keep the light-path dark while allowing the lens and tail boards to tilt and shift relative to one another.
  • Musical instrument
    Musical instrument
    A musical instrument is a device created or adapted for the purpose of making musical sounds. In principle, any object that produces sound can serve as a musical instrument—it is through purpose that the object becomes a musical instrument. The history of musical instruments dates back to the...

    s may employ bellows as a substitute or regulator for air pressure provided by the human lung
    The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

    • melodeon, concertina
      A concertina is a free-reed musical instrument, like the various accordions and the harmonica. It has a bellows and buttons typically on both ends of it. When pressed, the buttons travel in the same direction as the bellows, unlike accordion buttons which travel perpendicularly to it...

       and related instruments
    • Reed organ
      Reed organ
      A reed organ, also called a parlor organ, pump organ, cabinet organ, cottage organ, is an organ that generates its sounds using free metal reeds...

    • Pipe organ
      Pipe organ
      The pipe organ is a musical instrument that produces sound by driving pressurized air through pipes selected via a keyboard. Because each organ pipe produces a single pitch, the pipes are provided in sets called ranks, each of which has a common timbre and volume throughout the keyboard compass...

    • Some varieties of bagpipes
      Bagpipes are a class of musical instrument, aerophones, using enclosed reeds fed from a constant reservoir of air in the form of a bag. Though the Scottish Great Highland Bagpipe and Irish uilleann pipes have the greatest international visibility, bagpipes of many different types come from...

    • Harmonium
      A harmonium is a free-standing keyboard instrument similar to a reed organ. Sound is produced by air being blown through sets of free reeds, resulting in a sound similar to that of an accordion...

       and melodeon
      Melodeon (organ)
      A melodeon is a type of 19th century reed organ with a foot-operated vacuum bellows, and a piano keyboard. It differs from the related harmonium, which uses a pressure bellows. Melodeons were manufactured in the United States sometime after 1812 until the Civil War era...

    • Portative
      Portative organ
      A portative organ is a small pipe organ that consists of one rank of flue pipes, sometimes arranged in two rows, to be played while strapped to the performer at a right angle...

  • Piping expansion joint
    Expansion joint
    An expansion joint or movement joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials, to absorb vibration, to hold certain parts together, or to allow movement due to ground settlement or earthquakes...

    : 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)

External links

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