shaped cast iron passage B, containing the guide blades c, and regu lating sluice valves d. There are as many sluices as guide blades, The each guide blade having a sluice sliding vertically behind it. backs of the sluices are rounded, so as to make the contraction and deflection of the stream gradual. Each sluice is hung by a rod b from the iron ring a, which is raised and lowered by means of three rods marked c, so as to raise, lower, or close, the whole of the sluices at once. C is the drum or annular passage of the wheel, containing the vanes f. E is a disc, by which the drum is carried. The disc, drum, and vanes, may all be cast in one piece. F F is the hollow vertical shaft of the wheel, at the top of which is the pivot, supported upon the top of the fixed vertical spindle G, a, obliquity of the guide blades, ...22° to 25 Breadth of ring-shaped passages .20° to 30°. = from to of mean diameter of wheel. may be Least depths of openings between guide blades, and between vanes, from 2 inches to 6 inches. Depth of drum of wheel depth of openings x 2. = As to the work, efficiency, best speed, and volume of flow, see Articles 172, 173, 174, 175, 177, Division I., 178. The speed may deviate from the best speed to the extent of one quarter, without materially diminishing the efficiency. As to the effect of the sluices, see Article 179. To avoid the diminution of efficiency by the lowering of the sluices, double turbines have been used, consisting of a pair of concentric wheels made in one piece, supplied with water by a similar pair of concentric annular supply passages. Each of those passages has its own set of sluices, hung from an independent ring; so that either division of the double wheel can have its supply of water cut off at pleasure. Thus the power of the turbine can be varied in a proportion exceeding that of two to one, without the necessity for employing very contracted orifices, and consequently wasting energy. 181. Jonval's, or Koechlin's Turbine, the invention of M. Jonval, and made by Messrs. Koechlin & Co., resembles Fontaine's turbine, with the wheel working in a vertical suction pipe (Article 105) in which the pressure is below that of the atmosphere. This enables the wheel to be placed at any convenient elevation not exceeding the head equivalent to one atmosphere, above the level of the surface of the tail race, without incurring (as would be the case in the absence of the suction pipe) a loss of head equal to the drop from the bottom of the wheel to the water level of the tail race. The 182. Fourneyron's Turbine, one of the earliest and best known of turbines with guide blades, is an outward flow turbine. average ratio of the outer to the inner radius of the wheel is n=2, and the depth of the wheel is about equal to, or a little greater than the breadth of the crowns. An example is represented in figs. 75, 76, of which fig. 75 is a vertical section, and fig. 76 a sectional plan of the wheel and supply cylinder, showing the form and arrangement of the guide blades and vanes. A is the tank or penstock; B, the supply cylinder. This is the arrangement for moderate falls; for very high falls, the water may be brought down from a reservoir to the supply cylinder by a pipe, whose resistance must be allowed for in determining the available fall. The cylinder B consists of two concentric tubes: the upper is fixed: the lower slides within it like the inner tube of a telescope, and is raised and lowered by means of the rods b. Near the upper edge of the inner tube is a leather collar, to make the joint between it and the outer tube water-tight. The lower part a of the inner tube acts as a regulating sluice for all the orifices at once. It has fixed to its internal surface wooden blocks, so shaped as to round off the turns in the course of the water towards the orifices. The bottom of the supply cylinder is formed by a fixed disc C, which is supported by hanging at the lower end of a fixed vertical tube enclosing the shaft. the guide blades. Fig. 76. This disc carries D are the vanes of the wheel. In the example shown, the passages between the vanes are divided into three sets, or horizontal layers, by two intermediate crowns or horizontal ring-shaped partitions. The object of this is to secure that the passages shall be filled by the stream at three different elevations of the sluice, and so to diminish the loss of efficiency which occurs when the opening of the sluice is small. E is the disc of the wheel; F, its shaft; G, the tail race. The pivot at the lower end of the shaft is supplied with oil through a small tube seen in the figure, which is laid down one side and along the bottom of the tail race, and rises directly below the pivot. K H is a lever which supports the step of the pivot, and is itself supported by fixed bearings at K, and by a rod, L, which can be raised or lowered by a screw, so as to adjust the wheel to the proper level. 183. Various Outward Flow Turbines. An improvement in the regulating apparatus of Fourneyron's turbine, introduced by Mr. Redtenbacher, is to vary the supply openings when required, by raising or lowering the disc C which carries the guide blades, by means of a screw at the top of the tube to which it is fixed. This dispenses with the necessity for an internal sliding cylinder within the fixed supply cylinder. Another modification of the regulating apparatus of Fourneyron's turbine, by M. Callon, is to make the sliding vertical tubular sluice in several segments, which can be opened or shut separately. To prevent the drowning of Fourneyron's turbine, M. Girard added to it a bell, or fixed vertical cylinder with the mouth downwards, which dips into the tail race, and within which the wheel works. A sufficient quantity of air is enclosed in the bell to keep the surface of the water within it below the level of the wheel; and the gradual loss of this air by leakage and diffusion in the water is supplied by means of a small forcing pump. It is of course the level of the water in the tail race outside the bell, that is to be taken into account in estimating the available head. It is probable that the effect of this may be to make the best inside-surface speed a, r, and the maximum efficiency, the same as for parallel flow turbines, viz. : 1-k" being from 75 to 8, and on an average about 78. 184. Reaction Wheels.-This class of wheels, of which the theory has been given in Articles 176, 177, Division III., and 178, comprehends all turbines without guide blades, of which a great variety have been contrived and used. The earliest form, well known as "Barker's Mill," discharged the water from orifices in the ends of straight tubular arms projecting from a hollow shaft. The friction of the water in the arms caused considerable loss of energy. Tubular arms, curved in various ways, were afterwards employed; but it is obvious that in any curved arm the friction must be greater than in a straight arm of the same diameter. The best form is one more or less resembling fig. 70; that is, a hollow disc, with projections leading the water to nozzles of a form approximating to that of the contracted vein. In the figure there are two nozzles; but three are better calculated to insure steady motion, provided they are exactly similar and equal. The best mode of regulating the flow is that introduced by Messrs. Whitelaw and Stirrat, of having the regulating valves at the orifices of discharge. This insures nearly equal efficiency at all openings of the orifices. The best mode of making the water-tight joint between the supply pipe and disc is that sketched in fig. 77. A is the supply pipe; B, the wheel, or hollow disc; C, the vertical shaft; D, the neck of the wheel through which it receives the water. Near the end of the neck is an annular recess containing a cupped leather collar, within which fits a tube E. The outer edge of this tube, scraped to a true plane, is pressed by the pressure of the water over the equal area of the inner edge, against the truly plane surface of |