Our Blacksmith Two-Stage Bellows

sketch1The Museum of Early Trades & Crafts has a six-foot, two-stage bellos made in New Jersey by A. Bonnell. With funding from The 1772 Foundation, we were able to have Herb Kean restore this bellows which is part of our blacksmithing display.

Most people are familiar with the ordinary bellows that are used to help start a fire in the fireplace or outdoor grill. It has two paddle-shaped pieces of wood joined by a flexible material, usually leather. The lower paddle has a simple flap valve, which is nothing more than a hole in the lower paddle covered with a piece of leather tacked down along one side. The flap valve opens to allow air to enter the bellows when the paddles are pulled apart and is kept closed by air pressure when the paddles are brought together to force air out the nozzle. The result is an intermittent stream of air to the fire that is quite satisfactory for the purposes mentioned.

A blacksmith needs a much steadier flow of air to be able to control the heat of his fire. The solution to this problem, before the invention of the centrifugal blower, was the two-stage bellows. Its mechanism consists of three heart-shaped paddles joined by leather to form two chambers. Each chamber has a flap valve for controlling air flow, and the upper chamber has a nozzle for air to exit.

In operation, the middle paddle is fixed in position, the upper paddle is free to move up and down, and the lower paddle is raised or lowered by means of a rope or chain controlled by the smith.

sketch2Gravity pulls the lower paddle down, bringing air through the lower flap valve into the lower chamber as shown in the sketch above. Then, with the lower chamber full of air, raising the lower paddle closes the lower flap valve and forces air into the upper chamber through the upper flap valve as shown in the lower sketch. The upper paddle rises as its air supply is recharged. The smith then releases the tension on the rope and the lower paddle drops down, recharging the lower chamber air supply. While that is happening, its own weight causes the upper paddle to descend, creating pressure to keep the upper flap valve closed and forcing air out the nozzle. In effect, the upper chamber acts as a reservoir of air which feeds the nozzle while the lower chamber is being refilled.

The lower paddle is operated up and down by the smith at whatever speed provides the heat required. The result is not so smooth an airflow as the more modern centrifugal blower, but at least the intermittent “puffing” of the single-stage bellows is avoided.

 

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