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3. Turbines in which the water flows horizontally inwards ; vortex wheels.

We owe the invention of this class of turbines to one of my own pupils, Mr. James Thomson, C. E., of Belfast, and probably no turbines are more efficient or capable of more general application to every variety of fall than the vortex wheels which he has constructed. For this reason, and also because from their recent introduction they are less known than the varieties which have been longer in use, we shall illustrate them rather more fully with the aid of working drawings, supplied by Messrs. Williamson and Brothers of Kendal, who, we believe, have at present erected all which are employed in this country.

The peculiarity of these vortex wheels consists in the arrangement of the fixed guide blades on the outside of a circular chamber in which is placed the revolving wheel, so that the water flowing inwards strikes the curved plates of the revolving wheel tangentially, and leaves the wheel at the centre at a minimum velocity; the whirlpool created in the wheel chamber giving to this description of turbine its designation of vortex wheel.

Fig. 134 shows the general form of the guides and passages of

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Fig. 134.

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a vortex wheel; a a are the fixed guides, four in number, which direct the water tangentially into the passages of the wheel bb; after having done its work in these, the water leaves the wheel at the open passage at the centre c; 8 is the vertical shaft carrying the wheel and communicating its motion to the mill. The chamber in which the guide blades a a are fixed forms part of the supply chamber, and the supply of water to the wheel may be regulated by altering the position of the guide blades, and thus diminishing or increasing the area of opening For this purpose the guide blades are fixed on

gudgeons d d, near their extremities, and are connected by levers and links, so that they may be shifted simultaneously by a spindle. The inner radius of the wheel is usually half the external radius, and the obliquity of the inner ends of the vanes 20° to 30°.

The general principles of these turbines Mr. Thomson thus explained at the meeting of the British Association in 1852 :'The velocity of the circumference is made the same as that of the entering water, and thus there is no impact between the water and the wheel; but, on the contrary, the water enters the radiating conduits of the wheel gently, that is to say, with scarcely any motion in relation to their mouths. In order to attain the equalisation of these velocities, it is necessary that the circumference of the wheel should move with the velocity which a heavy body would attain in falling through a vertical space equal to half the vertical fall of water, or, in other words, with a velocity due to half the fall, and that the orifices through which the water is injected into the wheel chamber should be conjointly of such area that when all the water required is flowing through them it may also have a velocity due to half the fall. Thus one-half only of the fall is employed in producing velocity in the water, and therefore the other half still remains acting on the water in the wheel chamber at the circumference of the wheel in the condition of fluid pressure. Now, with the velocity already assigned to the wheel, it is found that this fluid pressure is exactly that which is requisite to overcome the centrifugal force of the water in the wheel, and to bring the water to a state of rest at its exit, the mechanical work due to both halves of the fall being transferred to the wheel during the combined action of the moving water and the moving wheel. In the foregoing statements, the effects of fluid friction, and of some other modifying influences, are, for simplicity, left out of consideration; but in the practical application of the principles, the skill and judgment of the designer must be exercised in taking all such elements as far as possible into account. To aid in this some practical rules, to which the author (Mr. Thomson) as yet closely adheres, were made out by him previously to the date of his patent. These are to be found in the specification of the patent, published in the Mechanics' Magazine for January 18 and January 25, 1851.'

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Mr. Thomson claims for his wheel the peculiar advantages(1) That the injection passages are large and well formed. (2) That it permits the employment of a most advantageous mode of regulating the power, by contracting the areas of the injection passages, without reducing the efficiency of the machine. (3) That the maximum velocity of the water in the wheel does not exceed that due to half the fall. (4) That the centrifugal action of the water tends to regulate the velocity of the wheels under a varying load.

In his paper, Mr. Thomson describes a vortex for a fall of 37 feet, and for an average supply of 540 cubic feet per minute, yielding 28 effective horse-power. The speed, 355 revolutions per minute; diameter, 22g inches; and extreme diameter of case, 4 feet 8 inches; also a low-pressure vortex for a fall of 7

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feet, for an average supply of 2,460 cubic feet per minute, and yielding 24 horse-power, at 48 revolutions per minute. Another he has constructed for a fall of 100 feet, and a fourth of large size, calculated for working at 150 horse-power, on a fall of 14 feet, and through a considerable part of the year submerged under 7 feet of backwater. These data will sufficiently show the capabilities of this machine, and its adaptation under great varieties of circumstances.

Figs. 135 and 136 exhibit an elevation and plan of a highpressure vortex wheel, constructed by Messrs. Williamson and Brothers of Kendal. It is of 5 horse-power, on a 30 feet fall, and consumes 118 cubic feet per minute. The water is conveyed to the wheel in the 9-inch pipe A A, at a velocity of 4.4 feet per second. B is the supply chamber, or wheel case, fixed on masonry in the tail-race c, from which the water passes away by the tunnel D. In the drawing the tunnel is shown closed, as is occasionally necessary, for access to the wheel or other purposes. E is a platform just above the ordinary level of the water; s s is the first motion shaft, to which the wheel is attached, and which is supported on the footstep at G, and by pedestals attached to the supply pipe a a. Fig. 137 shows the wheel case in section. chamber or guide blade chamber, cast in

н н is the supply parts and bolted

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together as shown; w, the wheel itself, about ten inches in diameter, and composed of wrought-iron plates with wrought-iron curved vanes; g g the four guide blades, in this wheel fixed and let into grooves cast in the cover and bottom of the chamber; K K, four bolts tying the cover and bottom of the supply chamber together to strengthen it against pressure; A the supply pipe as before, and K K the openings in the centre of the wheel

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