WATER WHEELS. The old "outward flow" and "inward flow" turbines have practically given place to the " inward and downward flow," as outlined by the Swain wheel (see APPLETON'S CYCLOPRDIA OF APPLIED AlEcuaNuGS); but the change from that wheel to those of less diameter, with deeper buckets, of longer curve, has been very decided, and resulted in higher efficiency, as well as greater economy in first cost. The following com parison illustrates this point.
77te Risdon Wheel.--The foregoing figures are taken from the published catalogues of the wheels, and are probably closely correct, although there is a discrepancy in the velocities, The inward portion of the discharge has been practically abandoned, the buckets being closed down to the bottom on a central core, and so curved as to throw the water out from the centre, as shown in Fig. 1 of the Risdon "D. C." or " double capacity " wheel mentioned above. This form of bucket appears to take advantage of the centrifugal motion given to the water by the wheel it self, and which in the ease of the (original) inward dis charge was directly opposed to the effect of the water.
Another cause of the displacement of the " outward discharge" wheel was the very poor result obtained at " part gate," or when the water was cut off by a sharp edged cylinder, or register, gate. Placing the gates externally has enabled them to be so formed as to deliver the water in an unbroken volume, by ajntages which contract the flow, instead of cutting it partially off.
Thus, while the Boyden dropped from an efficiency of 79 per cent. at full gate to 44 per cent. with hajf water ; and the Houston from 81 per cent. to 23 per cent. ; the " Risdon" falls from 87 per cent. to 70 per cent., and the " Hercules" from 87 per cent. to 74 per cent., in Professor Thurston's best test. The Risdon wheels at the Jefferson mill of the Amoskeag Manufacturing Co., Manchester, N. EP, consist of two pairs of 43-in., and one pair of 36-in. " D. C.," as shown in cut of bucket, and are all mounted on a 9-in. steel shaft, with couplings between the 93-in. and the 36-in., so that the latter. which draw water from a lower level, can be disconnected if desired. The head on the 43-in. wheels is 49 ft.;
that on the 30-in, ones is 28 ft., giving than the same circumferential velocity. at 225 rev olutions per minute.
Fig. 2 illustrates one of the most complete systems of horizontal-shaft turbines yet intro duced, viz.: that furnished by the Risdon Co. (previously described) for the Jefferson mill of the Amoskeag Co., at Manchester, N. If. It consists, as shown, of 6 wheels, in 3 pairs, on one shaft ; one pair, under a lower head. being of smaller diameter, so as to have the same surface velocity, or 62 per cent. of that due to the head.
These wheels themselves are all solid bronze castings, but the cases and draft tubes are cast-iron, and the feeder pipes boiler plate. Six small wheels were here adopted, in place of three large ones. as first suggested, to obtain higher velocity of shaft. smaller driving pulleys as a consequence, and the ability to use as large a proportion of the very variable quantity of water to the best advantage, or as near " full gate " as possible.
The Collins Wheel.—A form of gate, similar in effect to that used on the Fontaine turbine, exhibited by Messrs. Froment, Menrice & Co., in London, in 1851, and which may be called a "plunger gate." is used on the Collins " downward flow " turbine shown in Fig. 3. This form of gate raised the efficiency of the Collins wheel to 85 per cent. at full gate, and 66 per cent. with 0.565 water, which Pro fessor Thurston says is the best performance of a Jonval turbine on record, Another well-known form of the Jonval turbine is the " Geyelin," built by Messrs. R. D. Wood & Co., of Philadel phia. One of these wheels, as tested by the writer. at the Centennial Exposition in 1876, gave over 84 per cent. net effect, and practically the same result was obtained from a 7-ft. wheel of the same style at the John P. King mill, at Augusta, Ga., 475 horse-power having been realized by the last test. All this type of Jonval wheels give high results at "full gate," but are somewhat defective at " part gate." This name of " Jonval" is applied to wheels set with a " draft tube," and at some point on the fall, intermediate from the bottom to 28 or 30 ft. above it.