Page:Lowell Hydraulic Experiments, 4th edition.djvu/75

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Experiments on a model of a centre-vent water-wheel, with straight buckets.

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99. The author was led to this design by the consideration of the path of the water in passing through the wheel, according to the hypothesis in art. 83. It is a wheel well suited for low falls, in which the water, over the wheel, may stand at its natural height, without requiring a vertical shaft of great length. Its simplicity and cheapness, combined with its other good qualities as a hydraulic motor, must recommend it for many such situations.

100. Plate VII., figure 1, is a general plan, and figure 2, a vertical section of the apparatus.

Figure 3 is a vertical section through the apertures in the guides and wheel; the guides and buckets are omitted to avoid confusion in the figure.

Figure 4 is a horizontal section of part of the guides and buckets, showing, also, the path of the water in experiment 8, according to the hypothesis in art. 83.

$A$ is the wheel; the exterior diameter is 22 7/8 inches; the interior diameter is 19 1/2 inches; the height between the crowns, or $BC$, figure 3, is 2 13/16 inches; it carries thirty-six buckets, $EE$, figure 4, of steel, about 1/22 of an inch in thickness, fastened to the wheel by means of the wooden cushions $FF$, figure 3; the upper cushions are screwed to the disc $D$, and the lower ones to the crown $G$. The disc $D$ is of cast-iron, 3/8 inch thick, with a suitable hub by which it is connected with the vertical shaft.

$HH$ are guides of cast-iron, which direct the water into the wheel, and also support the plate $I$, which protects the wheel from pressure on its upper surface; the contraction of the streams entering the apertures between the guides, is diminished by the curved wooden garniture $K$; there are twenty-four guides. The mean shortest distance between the buckets at $ab$, figure 4, is 0.0339 feet; the mean shortest distance between the guides $cd$, figure 4, is 0.0437 feet; and the height of both is 2 13/16 inches = 0.2344 feet; we have, therefore, for the sum of the areas of the smallest sections between the guides,

$$0.0437\times 0.2344\times 24=0.24584\ {\text{square feet.}}$$