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sluices are partially closed, but it is exactly when the supply of water is deficient that it is most important to get out of it the greatest ossible amount of work. The im erection of P P the regulating arrangements is therefore, from the practical point of view, a serious defect. All turbine makers have sought by various methods to improve the regulating mechanism. B. Fourneyron, by dividing his wheel by horizontal diaphragms, virtually obtained three or more separate radial iiow turbines, which could be successively set in action at their full power, but the arrangement is not altogether successful, because of the spreading of the water in the space between the wheel and guide-blades. Fontaine similarly employed two concentric axial flow turbines formed in the same casing. One was worked at full power, the other regulated. By this arrangement the loss of efficiency due to the action of the regulating sluice affected only half the water power. Many makers have adopted the expedient of erecting two or three separate turbines on the same waterfall. Then one or more could be put out of action and the others worked at full power. All these methods are rather palliatives than remedies. The movable guide-blades of Professor James Thomson meet the difficulty directly, but they are not applicable to every form of turbine. C. Callon, in x840, patented an arrangement of sluices for axial or outward flow turbines, which were to be closed successively as the wa tk supply diminished. By preference the sluices were closed by pairs, two diametrically opposite sluices forming a pair. The water was thus admitted to opposite but equal arcs of the wheel, and the forces driving the turbine were symmetrically placed. As soon as this arrangement was adopted, portion of the sluice, and stopped each time it passes a closed portion of the sluice. It is thus put into motion and stopped twice in each rotation. This gives rise to violent eddying motions and great loss of energy in shock. To prevent this, the turbine wheel with partial admission must 'be placed above the tail water, and the wheel passagesmbe allowed to clear themselves of water, while passing from one open portion of the sluices to the next. . i y But if thewheel passages are free of water when they arrive at the open guide passages, then there can be no pressure other than atmospheric pressure in the clearance space between guides and wheel. The water must issue from the sluices with the whole velocity due to the head; received on the curved vanes of the wheel, the jets must be gradually deviated and discharged with a small final velocity only, precisely in the same Way, as when a single jet strikes a curved vane in the free air. Turbines of this kind' are therefore 'termed turbines of free deviation. There is no variation of pressure in the jet during the whole time of its action On 'the wheel, and the whole energy of the jet is imparted to the wheel, simply by the impulse due to its gradual change of momentum. It is clear that the water may be admitted in exactly the same way to any fraction of the circumference at pleasure, without altering the efhciency of the wheel. The diameter of the wheel may be made as large as convenient, and the water admitted to a small fraction of the circumference only. Then the number of revolutions is independent of the water velocity, and may be kept down to a manageable value. t § 198. General Description of an Impulse Turbine or Turbine with free Deviation.-Fig, 197 shows a general sectional elevation 'of a (Jirard turbine, in 1/ ah', ¢, . gg»r;y?, ; “" ' »é1*""r'" if L; lla tid! is rs. which the flow is axial. The water, admitted above a horizontal ffloor, passes down through the annular wheel containing the guide» blades (3, G, and 14 if v* » a a, Q it I

1 1 l, f rf '; ~ at thence into the revolving wheel. WW. The revolving wheel is fixed to a hollow shaft suspended from the pivot p. The solid interrlal shaft .rs .is merely a fixed column WMM The advantage pf this is that .the ivot is Fic.. 198. accessible for lubrication and adjustment. B is the mortise bevel wheel by which the power of the turbine is given off. The sluices 31, | - . c Ilfw ls l. ., . ., . .

. . l. - - "' -» V" *-'-5° I

r- l;=:e girl g ~-~ r, T' 1 lil na .1 'T — sa 'Q ii fiig, — - “ .., ... 2 2 T El' il!! flies.;-fs > Il *E* iii o 5 ia esse L , ,, , a modification of the mode of action of the water in the turbine became necessary. If the turbine wheel passages remain full of y water during the whole rotation, the water contained in each passage must be put into motion each time it passes an open are worked by the hand wheel h, which raises them successively, in a way to be described presently. d, d are the. sluice rods. Figs. 198, 199 show the sectional form of the guide-blade chamber and wheel and the curves of the wheel vanes and guide-blades, when drawn on a plane development of the cylindrical section of the Q Wheel; a, ct, a are the sluices for cutting off the water; b, b, b are, . apertures by which the E. -~—~, %, ,.|i. . entrance or exit of air is facilitated as the Q buckets empty and fill. Figs. zoo, 201 show the guide-blade gear. a, a, a p are the sluice rods as before. At the top of each sluice rod is a 6 'n small block c, having a project in ton uc, ,, - which slidei in gthe groove of the circular Q/ cam plate d, d. This ' ' Y '1 '-L-"f " -f"circular plate is sup- FIG 199 ported on the frame e, and revolves on it bymeans of the flanged rollers f. Inside, at the top, the cam plate is toothed, and gears into a spur pinion connected with the hand wheel h. At gg is an inclined groove or shunt. When the tongues of the blocks c, c arrive at g, they slide up to a second groove, or the reverse, accordin as the cam plate is revolved in one

direction or in the other. As giis operation takes place with each