A novel form of the Leffel wheel is known as the twin combination. This consists of two regularly built James Leffel wheels, either standard or special, placed within a large cylin drical wrought-iron casing, with cast-iron heads, the whole affair being substantially and durably built. Both wheels discharge the water toward each other, which unites and passes downward through a single central draft tube of large capacity. The changes in general design of the standard Leffel wheel which have been made of late years, consist in wider gates and correspondingly wider buckets. This arrangement secures a greatly enlarged capacity for water, and consequently a largely increased power for the same size of wheel ; affording a concentration of power in a smaller space.
The PPlton Wheel.—A novel type of wheel of a very different form from the turbine has been recently introduced on the Pacific Coast. It is applicable to very high heads and small streams of water, and has given very good results.
It might be approximately described as having "the outline of an undershot wheel, with the buckets of a turbine." Its general construction will be readily understood from Fig. 13. The important feature is the peculiar construction of the bucket. which is illus trated in section, Fig 14, and in perspective, Fig. 15. The thicket is in form of a paraboloid, and has a central wedge which splits the entering jet of water. This jet then passes to the right and left, following the curve of the bucket, and is discharged at its periphery, having imparted all its energy and motion to the wheel, and falling away as dead water. Mr. Boss E. Browne, hydraulic engineer of San Francisco, who has tested this wheel, reports an effi ciency of per cent. miller 50-ft. head, with a 15-in. wheel, and says that the velocity of the bucket should be one half that of the jut. Other tests of a 6-ft. wheel, by Messrs. Ed ward Coleman and George Fletcher, in 1884. showed an offiehmev of 87 per cent. In this case the velocity of bucket as compared to the theoretical velocity of jet was about 52 per cent.
The great simplicity and economy of construction of this wheel commends it to atten tion, and it is especially available for rery high heads and very small volumes of water. In the last test quoted. the head of water was 080 ft., the diameter of pipe, 22 in., and the diameter of nozzle through which it was delivered was 1.89 in. The power obtained is stated as 107 horse-power, and the revolutions of wheel per minute, 253/1. The water used is stated as 2.819 cub. ft. per second, or 169-14 rub. ft. per initiate.
Now, the Leffel wheel, one of the smallest turbine wheels in use. would use this amount of water under 1t0 ft. head, give horse-power, and make 2,080 revolutions per minute. This shows the advantage of this wheel in the number of revolutions to a more practical point, by the use of very small buckets on a wheel of large diameter. Were a turbine to be especially constructed for such a head. a wheel, having a diam eter of S in. at central point of discharge, would require to make 2.000 revolations per min ute to bring its velocity of discharge to that of the react conirgeta" under :180 ft., although a turbine of larger diameter, with small apertures, might undoubtedly lie designed for the purpose, like Mr. celebrated turbine of St Blaise.
The Pelton wheel has proved especially efficient in the electrical transmission of power.
and, as is illustrated in Fig. 16, may be placed directly on the dynamo shaft. The full-page repre sents an electric lighting station in which all the dyna mos are driven by these wheels. As examples of the use of the wheel for driving dynamos, the following may be noted: The power station of the American River Syndicate is located at lock Creek, Eldorado County, Cal. The plant consists of an 8-ft. Felton wheel, which, running un der a head of 110 ft. at 100 revolu tions with a 51-in. nozzle, has a maximum capacity of 130 horsepower. 'l'o this wheel is connected a 100 horse-power Brush generator, speeded at 900 revolutions, the current from which is carried to the mill through a single insulated copper wire, No. 3 B. & S. gauge, the return being made by a wire of the same size, making a four-mile circuit. The power from the generator is communicated to the countershaft of the mill by a 70 horse-power Brush motor running at 950 revolutions. The machinery operated consists of three centrif ugal roller mills, a ten-stamp battery, and a rock breaker. The Pelton wheel under these conditions shows an efficiency of 86 per cent., while about 75 per cent. of the power thus generated is available for duty at the mill. Sufficient power is taken from the main circuit to run sixty incandescent lamps for the entire works.
It only remains to be said that the modern turbine has been brought to such a point of perfection that, with proper attention to correct velocity of discharge and ample water pas sages, from 80 to 85 per cent. of the gross power of the water can be safely estimated as secured by 8 or 10 of the most popular types of wheel.
Way, Balancing : see Balancing Way.