Partial Turbine and Tangential 3 (pl. 68) represents in cross-section a tangential wheel or partial turbine. It consists of two wheels constructed according to Girard's system, which are struck by the flowing water at their lowest point. This illustration exhibits an example of a double turbine and also one with a vertical position of the wheel, con sequently with the shaft arranged horizontally.
The vertical wheel exhibited in Figure 4 (pl. 68) is intended particu larly for mining purposes and for small wheels under high heads where gearing is not only difficult to arrange and to keep in order, but is also frequently impracticable otherwise. The horizontal shaft of the water wheel, on which is placed a pulley, affords not only the simplest, but also the most efficient, means of connecting the power to the point where it is desired to be used. This is easily effected, and any desirable amount of power may be transmitted and motion obtained by properly proportioned pulleys with light but sufficient belting.
Figure 7 (pi. 65) illustrates a primitive form of water-wheel on the principle of a turbine. The current of water from the spout falls upon spoon-shaped radiating paddles, which are so set in the shaft that the side wise action of the falling water forces the paddles around and rotates the shaft. This construction is called a "spoon-wheel," and when surrounded by a cylindrical curb it is termed a " tub-wheel." The effect of such a wheel has been improved by projecting the current on the wheel tangen tially, as is shown in the Algerian mill on Plate 3 (fig. 3), and further improved in the Pelton wheel represented on Plate 64 (fig. I). A wheel similar to the spoon-wheel is employed in driving the Turkish mill shown on Plate 3 (fig. 5).
Constructive special importance for the effectiveness of turbines is the construction of the pivots. Horizontal shafts can readily
be provided with the usual bearings which are not exposed to unfavorable effects, but with most turbines having vertical shafts the pivots must run under water, where they are subjected to rapid wear, especially if inaccessi ble, by the percolation of the sand carried by the water into their sockets. To protect them in the latter respect, as also to admit of the application of lubricating oil and to effect their accurate vertical position, many widely-differing forms of construction and internal arrangements have been given to them, examples of which are exhibited in Figures i to 4 and 7 to To (pl. 67). There are also mechanical devices by which the pivot is relieved from these causes of wear by being extended above the water (pi. 65, figs. 1, 4; pi. 66, jigs. 7, 8; pl. 67, Jig. 3; pi. 68, jig. i). Figures 5 and 6 (pl. 67) especially represent, in cross-section, such an arrangement of the pivot, in which a hollow turbine-shaft and a stationary pivot-spindle reach ing from the tail-water to the head-water are used. Figure 4 (pl. 67) also shows such a construction. Figures 9 and io exhibit in plan and sectional elevation a pivot with three anti-friction wheels arranged above the water for decreasing frictional resistance.
Figures 3 and 4 (pl. 69) show, in vertical section and in plan, a glass sus pension-box designed to replace the "step" bearing of turbines. It is com posed of a circular disc, which is fastened to the inlet-casing, and in whose depressed portion are arranged stationary glass segments (B); the space around each segment allows a free circulation of the lubricant with which it is filled. On the glass segments revolves a metal ring (A) which is firmly secured to the turbine shaft.