Due to the variety of types of horizontal wheels and the fact that the way they work is not quite so obvious as in vertical wheels, we have given horizontal wheels the following expanded treatment.
The power of water may derive from impact as in a free-standing horizontal wheel, or in a tub wheel the power is derived from the sweep of the water as it is forced around the interior walls of the tub, imparting some of its force to push the paddles of the wheel along before falling through the bottom of the tub. “The wheels of our ancient mills consist of a simple nave, on the circumference of which are embedded floats, nearly always curved, and of different forms …. On some, the motive water is injected in an isolated vein, through a trough; others, placed at the bottom of a tub open beneath, are impelled by the whirl of water cast upon them.” [D’Aubuisson de Voisins p. 406] “… horizontal mill[s] (moulin à trompe; regolfo mill) utilized an enclosed masonry conduit, usually of circular or pyramidial shape, to lead water under a moderately high head to a spout which directed an isolated jet of water against a horizontal wheel with curved blades or a helical rotor. [Terry S. Reynolds. Stronger Than a Hundred Men: A History of the Vertical Water Wheel. Baltimore: The Johns Hopkins University Press, 1983.p. 159]
Tub wheel; Moulin à cuve
Tub wheels were placed in a tub or cylinder.
Reynolds: “The second type of horizontal mill (moulin à cuve; tube mill) had a horizontal wheel with curved blades or a helical rotor placed at the bottom of a close-fitting masonry cylinder.” [Terry S. Reynolds. Stronger Than a Hundred Men. A History of the Vertical Water Wheel. Baltimore, 1983]
Voisins: “… The motive water, after having passed under the gate at the entrance of the course, is borne with rapidity upon the adjacent part of the cylindric wall of the pit; in striking, it is at first considerable raised; then following its circuit, it descends and reaches the floats, upon which it acts by impact and its weight; it bears them along in its whirl.” [D’Aubuisson de Voisins p. 411-412]
“… [Tub wheels], placed at the bottom of a tub open beneath, are impelled by the whirl of water cast upon them.” [D’Aubuisson de Voisins p. 406]
Evans: “A tub mill has a horizontal water-wheel, that is acted on by the percussion of the water altogether; the shaft is vertical, carrying the stone on the top of it, and serves in place of a spindle … the water is shot on the upper side of the wheel, in the direction of a tangent with its circumference. … The wheel runs in a hoop, like a mill-stone hoop, projecting so far above the wheel as to prevent the water from shooting over the wheel, and whirls it about until it strikes the buckets, because the water is shot on in a deep narrow column … —the whole of this column cannot enter the buckets until a part has passed half way round the wheel, so that there are always nearly half the buckets struck at once; the buckets are set obliquely, that the water may strike them at right angles. … As soon as it strikes, it escapes under the wheel in every direction, as in fig. 29.* [Oliver Evans. The Young Mill-Wright and Miller’s Guide. Twelfth ed. with Additions and Corrections by Thomas P. Jones, Philadelphia, 1848. p. 159-160]
… If the head be low, it is with difficulty we can put a sufficient quantity of water to act on them so as to drive them with sufficient power; I, therefore, advise to let the water strike on them in two places; as in Plate IV, Fig. 29; the apertures need then only be about 6 by 13 inches each, instead of 9 by 18; they will then operate to more advantage, as nearly all the buckets will be acted on at once.
The following was taken from www.porslanvers.eu:
Dans son “Architecture Hydraulique”, Bélidor nous donne la description du moulin de Basacle à Toulouse. Voici comment il présente la roue : Le coursier aboutit à un cylindre ou tonneau sans fond, qui est de maçonnerie. L’eau entre avec précipitation dans le coursier & s’introduit dans le tonneau en formant un tourbillon… L’eau qui entre dans le tonneau, après avoir fait plusieurs tours & frappé les aubes de la roue, s’échappe par le vide qui se trouve dans l’intervalle que ces mêmes aubes laissent entr’elles, sort par le fond du tonneau, & s’écoule du côté aval où on a ménagé une pente.
Rough translation: The trough ends at a cylinder (tub) without a bottom which is made of masonry. The water enters by precipitation (falling) flowing along the trough and introduces itself into the cylinder by forming a whirl (vortex) … the water that enters the cylinder, after having made several turns and hit the blades (vanes) of the wheel, slips away (escapes) through the space between the blades, leaves by the bottom of the cylinder and runs off downstream.