Page:Lowell Hydraulic Experiments, 4th edition.djvu/37

 In experiment 92, resin oil and a small stream of water were used.

43. A special apparatus was provided to indicate the direction in which the water left the wheel. For this purpose the vane P, figures 1, 6, and 7, plate IV., was placed near the circumference of the wheel, and was keyed on to the vertical shaft Q, which turned freely on a step resting on the wheelpit floor. The upper end of the shaft carried the hand R, figures 1 and 4, and directly under the hand was placed the graduated semicircle S, divided into 180°. When the vane was parallel to a tangent to the circumference of the wheel, drawn through the point nearest to the axis of the vane, and the vane was in the direction of the motion of the wheel, the hand pointed at 0°, and, consequently, when the vane was in the direction of the radius of the wheel, the hand pointed at 90°. To prevent sudden vibrations of the vane, a modification of the hydraulic regulator was attached to the lower part of the vane shaft. This apparatus is represented in detail by figures 6 and 8.

44. The quantity of water discharged by the wheel was gauged at a weir erected for the purpose at the mouth of the wheelpit. It is represented on plate V.

Figure 1 is a plan, and figure 2 a section, showing the relative positions of the turbine A, the grating B, the gauge box C, and the two divisions or bays of the weir, D, and E.

As the water issued from the orifices of the turbine with considerable force, particularly when the velocity of the wheel was much quicker or slower than that corresponding to the maximum coefficient of effect, there were often such violent commotions in the wheelpit, that, unless some mode was adopted to diminish them before the water reached the weir, or even the place where the depths on the weir were measured, it would have been impossible to make a satisfactory gauge of the water. For this purpose the grating B, figures 1 and 2, was placed across the wheelpit. This grating presented numerous apertures, nearly uniformly distributed over its entire area, through which the water must pass. In the experiments with a full gate, the fall from the upper to the lower side of the grating was generally from three to four inches. The combined effect of this fall and of the numerous small apertures, was, to obliterate almost entirely the whirls and commotions of the water above the grating. About 4.5 feet in length of the grating between F and G, figure 1, was so nearly closed, that but little water passed through that part of the grating; — this made it very quiet in the vicinity of the gauge box C.

Figure 3, plate V., is an elevation of the weir. The two bays D and E were of nearly equal length, — the crest of the weir was almost exactly horizontal, and the extreme variation did not exceed 0.01 inch. The crest of the weir was of cast-iron, planed on the upper edge H, figures 2 and 4, and also on the upstream face, to a point 1.125 inches below the top; — below this, at I, figure 4, there was a small bevel, 3