bellows

Bellows are devices that create a controlled, directed flow of air by alternately expanding and contracting a flexible chamber. When the chamber enlarges, air is drawn in through a one-way valve; when it contracts, the air is expelled through a nozzle via another valve. This results in a concentrated jet of air that can intensify a flame or supply a steady flow to a pneumatic device.

There are several types used for different purposes. Fireplace and forge bellows are common in metalworking and heating; they often consist of a leather or canvas bladder mounted between rigid boards and operated by hand or foot to deliver a powerful blast to a furnace. Organ bellows and other musical bellows provide a continuous supply of air to pipes, enabling wind instruments to sound. In both cases, bellows can be single-acting, delivering air on one stroke, or double-acting, delivering air on both strokes. Some modern variants use mechanical or electric power to automate the pumping action.

Construction typically involves a flexible bag or chamber (often leather, canvas, or synthetic material) connected to wooden or metal frames, with valves to control air entry and exit. A nozzle directs the air to its target, whether a pipe, a forge fire, or a glass furnace. The efficiency of a bellows depends on the seal of the chamber, the smoothness of the pumping action, and the design of the valves.

Historically, bellows date to ancient times and have played a crucial role in metallurgy, glassmaking, and music. They remain useful in traditional crafts, as well as in modern pneumatic systems and educational demonstrations.