Page "Bellows" Paragraph 16

Double-acting piston bellows are a type of bellows used by blacksmiths 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 at least since the 5th century BCE, when it was invented, and had reached Europe by the 16th century.