All components of the wind system instrument and those of the instrument are based mostly on historical principles⁴.

the breath:

The basic components of the wind system consist of a large reservoir and two pedal-pumped feeder bellows. The only materials are wood and leather. The cuneiform, or wedge-shaped reservoir is 2’ x 5’ with 5 pairs of folding ribs. The ribs have been hinged together in such a way that they never actually touch each other when they fold. Consequently, the action of the system is very quiet. The folded ribs rest upon a 3 1/2” perimeter wall, the trunk band, into which is let the rectangular wind trunk (3” x 11”), the pipe which conducts air to the wind chest. The active volume of the reservoir is about 10 cu’. Hanging from the underside of the reservoir’s bottom board like a pair of bats, are two cuneiform feeder bellows each with one folding rib pair. Each feeder is 2’ x 2’ and about 1/2 cu’ in volume. The feeders ‘inhale’ from the room and ‘exhale’ into the reservoir by means of simple, quiet leather flap valves. The feeders are pumped by the alternating action of two large pedals, one attached to the leading edge of each feeder bottom board. The pedals are designed kind’a like giant harpsichord keylevers, balanced half way along their length. Because the player is directly in control of the breathing of the organ through the pump pedals, unusual expressive devices can be effected, which can sound somewhat like the ‘bebung’ of the clavichord. Tolerances and methods of construction employed in the self-pumped wind system are easily within the grasp of the Medievals, and it is curious why such a system has not yet appeared in the fossil record. Because I am completely wrong is, on the other hand, the most likely possibility. On the other hand, one wonders what the angel’s robe may be hiding in Van Eyck’s famous triptych with organ of 1434.⁵ But I suppose if the choice were between pump pedals and Van Eyck’s lovely drapery, I, too, would have opted for the drapery.

4a. Bedos de Celles, Dom Francois, L'Art du facteur d'orgues, Paris, 1766-1778
4b. Diderot, Denis, and Jean le Rond d'Alembert, eds., Encyclopedie ou Dictionnaire Raisonne des Sciences, des Arts, et des Metries, Paris, 1751-1758
4. two stops employ ideas from Audsley’s marvelous wooden pipe description
Audsley, G.A., The Art of Organ Building, Dodd, Mead, N.Y.,1905
5. ‘Adoration of the Mystic Lamb” Jan Van Eyck, 1434, Ghent