MACHINERY.] HYDROMECHANICS 527 selected as the type of reaction turbines. It is one of the best even in normal conditions of working, and the mode of regulation introduced is decidedly superior to that in most reaction turbines ; it might almost be said to be the only mode of regulation which satisfies the conditions of efficient working, and it has been adopted in a modified form in the Leffel turbine, which is now largely used in America. Figs. 185 and 186 are external views of the turbine case ; figs. 187 and 188 are the corresponding sections ; fig. 189 is >J Fig. 189. the turbine wheel. The example chosen for illustration has suction pipes, which permit the turbine to be placed at any height less than 30 feet above the tail-water level. The water enters the turbine by cast-iron supply pipes at A, and is discharged through two suction pipes S, S. The water on entering the case distributes itself through a rectangular supply chamber SC, from which it finds its way equally to the four guide-blade passages G, G, G, G. In these passages it acquires a velocity about equal to that due to half the fall, and is directed into the wheel at an angle of about 10 or 12 with the tangent to its circum ference. The wheel W receives the water in equal propor tions from each guide-blade passage. It consists of a centre plate;? (fig. 189) keyed on the shaft aa, which passes through stuffing boxes on the suction .pipes. On each side of the centre plate are the curved wheel vanes, on which the pressure of the water acts, and the vanes are bounded on each side by dished or conical coverplates c, c. Joint- rings j. j on the cover plates make a sufficiently water tight joint with the casing, to prevent leakage from the guide-blade chamber into the suction pipes. The pressure near the joint rings is not very great, probably not one- fourth the total head. The wheel vanes receive the water without shoi k, and deliver it into central spaces, from which it flows on either side to the suction pipes. The mode of regulating the power 01 the turbine is very simple. The guide-blades are pivoted to the case at their inner ends, and they are connected by a linkwork, so that they all open and close simultaneously and equally. In this way the area of opening through the guide-blades is altered without materially altering the angle or the other conditions of the delivery into the wheel. The guide-blade gear may be variously arranged. In this example four spindles, passing through the case, are linked to the guide-blades inside the case, and connected together by the links I, I, I on the outside of the case. A worm wheel on one of the spindles is rotated by a worm d, the motion being thus slow enough to adjust the guide-blades very exactly. These turbines are made by Messrs "Williamson Brothers of Kendal, who supplied the drawing of the turbine. Fig. .190 shows another arrangement of the same turbine, with some adjuncts not shown in the other drawings. In this case the turbine rotates horizontally, and the turbine case is placed entirely below the tail water. The water is supplied to the turbine by a vertical pipe, over which is a wooden pentrough, containing a strainer, which prevents sticks and other solid bodies getting into the turbine. The turbine rests on three foundation stones, and, the pivot for the vertical shaft being under water, there is a screw and lever arrange ment for adjusting it as it wears. The vertical shaft gives motion to the machinery driven by a pair of bevel wheels. On the right are the worm and wheel for working the guide-blade gear. 174. Different Forms of Turbine Wheel. The wheel of a turbine or part of the machine on which the water acts is an annular space, furnished with curved vanes dividing it into passages exactly or roughly rectangular in cross section. For radial How turbines the wheel may have the form A or B, fig. 191, A being most usual Fig. 191. with inward, and B with outward flow turbines. In A the wheel vanes are fixed on each side of a centre plate keyed on the turbine shiii t. The vanes are limited by slightly-coned annular cover plates. In B the vanes are fixed on one side of a disk, keyed on the
shaft, and limited by a cover plate parallel to the disk. Parallel
