The draft tube was patented in the United States by Zebulon and Amasa Parker, of Licking, 0., in 1840. It has proved of great value, by enabling turbines to be set on hori zontal shafts.
Figs. 4 and 5 illustrate the construction of the Geyelin turbine constructed for Cornell University, by Messrs. R. I). Wood & Co. The turbines are 34 in. in diameter, and are calculated to produce 175 horse-power at 40 ft. head. Their speed is 253 revolutions per minute. Mr. Geyelin has devised a novel and effective form of glass suspension stop. which is illustrated in cross section in Fig. 6. The revolving disk, A, which supports the wheel, rests on the glass disks, B B.
The Hunt Wheel has since been improved by the addition of " ajutages " to the gate, bringing the half-water effect up to 66 per cent. These " ajutages " are shown in Fig. 7, appearing between the chutes. The next great step in turbine construction has been to set them on horizontal shafts, and, when practicable, in pairs, so as to thrust against each other, and neutralize step friction.
Glynn, in his Treatise on Water Power (John Weale, 1853), speaks of this method as being advised by Pro fessor Wedding, of Berlin, for the Archimedian scroll wheels, to save step and gear friction. About 1861, the late John C. Hoadley put in a scroll wheel of this sort-, in Manches ter. N. H., and the writer followed it within two years later by seven small iron turbines, set in iron pipes, singly, and in 1870 the Swain Turbine Co. put in a pair of wheels in this manner at Ticonderoga, and the plan is now adopted by all prominent turbine builders.
Fig. 8 shows the external case of a pair of Hunt wheels set in this manner with central draft tube. This method of setting saves not only the cost of bevel gears, but the loss of power by their friction, commonly estimated at about 5 per cent. Two tests of a. Hunt wheel, at the Holyoke testing flume (on vertical shaft), by Mr. Herschel. gave respectively .8000, and per cent. effect, and the same wheel, on horizontal shaft, in the mill at Lowell, was tested by Mr. Francis, giving .8030 and .8036 per cent.
The Humphrey Wheel has a " paraboliform curve of crown and chutes," so as to deliver the water to the wheel in a tangential direction, and also in the natural form of discharge due to the " vena contracta." The buckets are not closed
down to the bottom on the outside, but have a free outward delivery, as seen at K, Fig. 9. Another point claimed is the redaction in number of the guides or chutes, thus saving friction, before the water reaches the wheel itself, and offering less obstruction to the passage of small floating mat ter, such as leaves or sawdust and chips. The discharge of water from any wheel should be such that its total velocity should be imparted to the wheel, and that the water should fall away " dead," thus doing away entirely with the theory of any result from "reaction." The writer has obtained the best results, from nearly all the wheels which he has tested, when the velocity of the wheel at the point of central discharge was from GO to 62 per cent, of the theoretical velocity due to the head, or to the velocity due the "contracted vein." A very large wheel of this type, 100 in. diameter, using 214 cub. ft. water per second, under 12.1 ft. fall, tested by Mr. Francis, at Lowell, in 1883, gave, over 240 horse-power, or about 82 per cent. net effect, at full gate, and 56 per cent. with half water, or per cent. gate opening.
The Victor Turbine, built by the Stilwell & Bierce Co , of Dayton, 0., is a popular and effective form of the latest modern turbine, with deep openings, and long curved buckets, discharg ing downward and outward. Fig. 10 represents the wheel separately.
Reliable tests of the Victor wheel show an effi ciency of from 80 to 89 per cent. at full gate, the higher effect being obtained from a very small wheel, 15 in. diameter, this being the usual result from all forms of turbine. The efficiency at one-half water, which must be distinguished from " half gate," is about 50 per cent. with the register gate, but a cylinder gate with ajutages is promised on this wheel. To show the power and effect of one of these small wheels, we give a record of tests of a 15-in. Victor, made a few years since at the Holyoke testing flume, in the course of some experi ments to determine the friction of gearing. The wheel had been tested on its own shaft previously, by James Emerson, giving a net effect of 92.58 per cent., or 30.62 horse-power, at 348'5 revolutions per minute, and these tests show a loss of about 3 per cent. due to the gears.