Hydraulics

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1907 Excerpt: ...By means of the screw, the hook is raised slowly, until, by piercing See section 82. the surface of the water, it causes a distortion of the light reflected from the surface. On moving the hook downwards again very slightly, the exact surface will be indicated when the distortion disappears. A more elaborate hook gauge, as used by Bazin for his experimental work, is shown in Fig. 152. For rough gaugings a post can be driven into the bed of the channel, a few feet above the weir, until the top of the post is level with the sill of the weir. The height of the water surface above the top of the post can then be measured by any convenient scale. 154. Gauging the flow in pipes; Venturi meter. Such methods as already described are inapplicable to the measurement of the flow in pipes, in which it is necessary that there shall be no discontinuity in the flow, and special meters have accordingly been devised. For large pipes, the Venturi meter, Fig. 153, is largely used in America, and is coming into favour in this country. The theory of the meter has already been discussed (p. 44), and it was shown that the discharge is proportional to the square root of the difference H of the head at the throat and the bend in the pipe, or k being a coefficient. For measuring the pressure heads at the two ends of the cone, Mr W. G-. Kent uses the arrangement shown in Fig. 154. Fig. 155. Recording drum of the Kent Venturi Meter. See page 46. The two pressure tubes from the meter are connected to a U tube consisting of two iron cylinders containing mercury. Upon the surface of the mercury in each cylinder is a float made of iron and vulcanite; these floats rise or fall with the surfaces of the mercury. Fig. 156. Integrating drum of the Kent Venturi Meter. When no water is passing t...