Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/548

532 532 .above a horizontal floor, passes down through the annular wheel con taining the guide-blades G, G, and thence into the revolving wheel WW. The re- fl 1 fl fl volving wheel is fixed to a hollow shaft suspended from the pivot p. The solid inter nal shaft ss is merely a fixed column support ing the pivot. The advantage of this is that the pivot is accessible for lubrication and adjustment. B is the mortise bevel wheel by which the power. 1Q7 of the turbine is given off. The sluices are worked by the hand wheel h, which raises them successively, in a way to be described presently, ft, a are the sluice rods. Figs. 197, 198 show the sectional form of the guide- blade chamber and p= wheel and the curves of the wheel vanes and guide- blades, when drawn on a plane develop ment of the cylin drical section of the wheel ; a, a, a are the sluices for cut ting off the water ; b, b, b are apertures by which the en trance or exit of air is facilitated as the buckets empty and fill. Figs. 199,200 show the guide- blade gear, a, a, a are the sluice rods as before. Fig. 198. At the top o. each sluice rod is a small block c, having a projecting tongue, which slides in the groove of the circular cam plate d, d. This circular plate is supported on the frame e, and Fig. 199. revolves on it by means of the flanged rollers/. Inside, at the top, the cam plate is toothed, and gears into a spur pinion connected with the hand wheel li. At gg is an inclined groove or shunt. d : a. J_ u u u uTrnrrn ~T~ o ~u r 1 y y y Fig. 200. When the tongues of the blocks c, c arrive at g, they slide up to a second groove, or the reverse, according as the cam plate is revolved [HYDRAULICS. in one direction or in the other. As this operation takes place with each sluice successively, any number of sluices can be opened or closed as desired. The turbine is of 48 horse power on 5 12 feet fall, and the supply of water varies from 35 to 112 cubic feet per second. The efficiency in normal working is given as 73 per cent. The mean diameter of the wheel is 6 feet, and the speed 27 4 re volutions per minute. 1 184. Theory of the Impulse Turbine. The theory of the impulse turbine does not essentially differ from that of the reaction turbine, except that there is no pressure in the wheel opposing the discharge from the guide-blades. Hence the velocity with which the water enters the wheel is simply where ft is the height of the top of the wheel above the tail water. If the hydropneumatic system is used, then ft = 0. Let Q OT be tho maximum supply of water, r lt r. 2 the internal and external radii of the wheel at the inlet surface ; then Wj&amp;gt; The value of ,- may be about 45 /20(H - ft), whence r,, r 2 can be determined. The guide-blade angle is then given by the equation _ vi _0-45_. 4g. 7 = 29. The value of, should, however, be corrected for the space occupied by the guide-blades. The tangential velocity of the entering water is Wi = vt cos 7 = -82 /2&amp;lt;/(H-fi). The circumferential velocity of the wheel may be (at mean radius) V,-=0-5/2#(H-ft). Hence the vane angle at inlet surface is given by the equation i__0 - 82-0-5_. 71 . 0-45~ The relative velocity of the water striking the vane at the inlet edge is Vn Ui cosec = l 22tf,-. This relative velocity remains unchanged during the passage of the water over the vane ; conse quently the relative velocity at the point of discharge is r ro = 1 22w,-. Also in an axial flow turbine V = V,-. If the final velocity of the water is axial, then y COS 4&amp;gt; = - = ,-^ = 0-5 1-22x0-45 = cos 24 This should be corrected for the vane thickness. Neglecting this, = iVo sin0 = tvi sin &amp;lt;f&amp;gt; = in cosec 6 sin0 = 5if,-. The discharging area of the wheel must therefore be greater than the inlet area in the ratio of at least 2 to 1. In some actual turbines the ratio is 7 to 3. This greater outlet area is obtained by splaying the wheel, as shown in the section (fig. 198). 185. The Hydraulic Ram. The hydraulic ram is an ar rangement by which a quantity of water falling a distance h forces a portion of the water to rise to a height 7^, greater than h. It consists of a supply reservoir (A, fig. 201), into which the water enters from some natural stream. A pipe s of considerable length conducts the water to a lower level, where it is discharged intermittently through a self-acting pulsating valve at d. The supply pipe s may be fitted with a flap-valve for stopping the ram, and this is attached in some cases to a float, so that the ram starts and stops itself automatically, according as the supply cistern fills or empties. The pipe s should be as long and as straight as possible, and as it is subjected to considerable pressure from the sudden arrest of the motion of the water, it must be strong and strongly jointed, d is an air vessel, and e the delivery pipe leading to the reservoir at a higher level than A, into which water is to be pumped. Fig. 202 shows in section the construction of the ram itself, d is the pulsating discharge valve already mentioned, which opens inwards and downwards. The stroke of the valve is regulated by the cotter through the spindle, under which are washers by 1 The drawings of this turbine have been taken partly from Meissuer, Die Hydraulik, partly from Uhland, Skizzenbuch.