Fourneyron Turbinc.—To overcome this imperfection, which was rec ognized before the erection of Cadiat's wheel, Fourneyron, in 1827, placed in the interior of the wheel a stationary deflecting apparatus called the "guide" or "directrix." In Figure 2, which represents a section in plan of both parts, that having the smaller diameter exhibits Fourney ron's guiding device, which is stationary, while that having the larger diameter is the revolving or turbine-wheel. The directrices, identified in the illustration by the heavy black lines, have a curvature opposite the curvature of the buckets of the turbine wheel, so that the water in passing from the guide into the turbine-wheel would, if the latter were stopped, be diverted in a sharp bend opposite to the direction given to it by the direc trices of the guide.
Turbine. — Figure 4 exhibits Fourneyron' low-pres sure turbine-wheel, and also represents a cross-section of the upper and lower water-channels. The turbine-wheel is connected with the shaft by means of a dish-like wheel composed of a system of radial arms, from which the water flows into the lower channel B. Into the interior of this wheel projects a cast-iron cylinder (cylindrical flume), which by means of a piston-like packing is tightly enclosed by a second cylinder. The inner cylinder can be raised or lowered between the turbine-wheel and the direc trix apparatus by the vertical rods seen in the Figure, so that the influx of the water can be partially or entirely shut off. The outer cylinder is tightly fixed in the wooden flooring so that the water passing (at A) into the upper chamber, which is completely enclosed by two brick channel-walls (G) and a wooden partition (Ii), can escape into the lower chamber only through the wheel. The vertical cast-iron tube (seen in the centre of the picture) is likewise secured in a flooring above. It carries on its lower end the directrix apparatus, and encloses the shaft, which is provided cog-wheel on its upper projecting-end, and the turbine-wheel on its lower end, supported by a pillow-block resting on a lever by which the wheel can be shifted vertically.
High-pressure nrbine.—The form of construction exhibited in Fig ure 3 (p.65) is Fourueyron's high-pressure turbine-wheel. It consists of a cast-iron cylindrical turbine chamber (A), provided with a securely-fitted cover, and rests upon the timber-work D over the lower water-channel. The influx of the water to the turbine chamber A is effected by means of a pipe (11) which extends to and is connected with the head-water channel or reservoir. The inflowing water, which would escape from the top of the cylinder were it not for the bolted cover, stands in the chamber A under high pressure, and hence the designation of "high-pressure" turbine in contradistinction to the low-pressure turbine above described. The shaft provided with the transmitting cog-wheel G and the rods of the cylindri cal gate, which are moved by the crank and crank-shaft (a) by means of the gearing shown, pass through and are guided by stufling-boxes in the cover of the turbine chamber.
In respect of a very small turbine erected at St. Blasicn, according to Fourneyron's system, Redtenbacher reported that, notwithstanding its greatest diameter was only t2;_ inches and its inner diameter 7;26 inches, it produced an effect of forty-seven horse-power. Of course the height of fall of the water acting on the wheel was fully roS metres (354 feet), while the current of water amounted to 115 feet per second, and the wheel had the enormous velocity of twenty-three hundred revolutions per minute. With such velocities, resulting from an excessive height of fall, the pivots are subjected to considerable wear. The main shaft and pivot are of steel, the wheel of wrought iron, and the other parts of cast iron.
Francis's of placing a directrix apparatus in the interior of the turbine-wheel, as in the Fonrneyron system, the reverse of this arrangement can be made. Constructions of this type are some times called Francis's turbines, after an American inventor who spent much time in experimentation in perfecting these turbines. They are also called American or "externally-moved " turbines, in contradistinc tion to the previously-described wheels, which are designated as " inter nally-moved" turbines. Various forms of Francis's turbines are shown on Plate 65 (figs. 5, 6) and Plate 66 (figs. 1-3), which, however, do not represent, in respect of external appearance and incidental details, Fran cis's original construction.
Figure 6 (pi. 65) exhibits a Francis turbine with many of its com ponent parts omitted to give a view of its interior construction. The supply-pipe A is of rectangular cross-section ; B is the turbine-wheel which is connected with the shaft C by the arms c, c, c; and a, a, a arc the directrices to the paddles D, D, D of the turbine-wheel. The influx of the water is in the direction of the arrows in the tapering, spiral sup ply-pipe A, around and outside the guides; hence to this form of con struction the term " spiral " turbine is sometimes applied. In Figure 5 the directrix apparatus is omitted, the influx of the water being directly to the wheel. The arrows indicate the direction of the inflow ing water. The turbine-wheel D with its connecting arms C, C and shaft A, together with the bevel-gears, the transmitting shaft B, and pul ley /, is readily distinguished. The prototype of Francis's turbine was au American invention called Howd's turbine, after its inventor, and was first used in the United States. It was simply constructed of wood and provided with straight directrices and turbine paddles. Figures i to 3 (pi. 66) show an improved construction of iron. Figure i is the directrix apparatus with straight paddles; Figure 2 is the turbine-wheel with curved paddles, and also the cover of the wheel-box or casing; and Figure 3 illus trates the manner in which the directrix is combined with the wheel-box.