The Supply and Uses of Water 



241 



With the velocity determined, they calculate what must be the 

 proper velocity of the rim of the wheel. Then they plan for 

 such a diameter of the wheel, and size of dynamo, as will give 

 the proper speed to the buckets and secure the maximum amount 

 of energy from the falling water. 



The amount of work that a Pelton water wheel delivers for 

 useful purposes (page 245) is unusually large in comparison with 

 machines depending upon fuel. With a medium high fall of 

 ten to twelve hundred feet, a wheel of ten to twelve feet in 

 diameter will put out in useful work from eighty to eighty-five 

 per cent of the total energy put in by the falling water. This 

 is nearly six times the amount of useful work a steam engine 

 performs with an equivalent amount of energy furnished in fuel. 

 It is also more efficient than the undershot wheel, which it 

 resembles in some respects. 



The water turbine. The water turbine is adapted to large 

 quantities of water with a low head or fall. The head may 

 vary from three feet to six 

 hundred feet. In the usual 

 style of turbine the water is 

 admitted all around the cir- 

 cumference of the wheel 

 through jets. It is deflected 

 by guides upon the blades 

 of the wheel, and as these lie 

 across its pathway to the 

 center of the wheel where it 

 escapes, it pushes them to 

 one side, thus making the 

 wheel rotate. This is shown 

 in the diagram of Fig. 71. 

 Turbines may be horizontal 

 with vertical shafts, or ver- 

 tical with horizontal shafts. 



CASINO 



FIG. 71. Turbine water wheel. Sec- 

 tion through wheel and guides viewed from 

 above. 



They are made with one wheel, 



or with two wheels fastened to one shaft. The twin- wheel 



