CHAPTER VIII 



HYDRAULIC EQUIPMENT 



1. TURBINES 



MODERN turbines may be divided into two classes: Pressure, 

 reaction or Francis turbines. Pressureless, impulse or Pelton 

 turbines. 



Reaction Turbines. This type is a combined potential and 

 kinetic energy wheel, or more properly speaking a turbine, since it 

 admits water all around the "periphery of the runner and all parts 

 of the same perform useful work. The water enters the runner 

 at a speed which is lower than -the spouting velocity, and a pres- 

 sure head is left to be used for the acceleration of the flow of water 

 through the runner. 



The water may pass either radially inward or outward or it 

 may enter the runner radially toward the shaft but leave in an 

 axial direction, i.e., in a direction parallel with the shaft. In 

 this case the turbine is of the mixed-flow type, this being most 

 extensively used in this country. 



The runner rotates partly from velocity action and partly 

 from reaction due to pressure and consequent acceleration in 

 buckets. As the draft tube is closed, the runner is full of water 

 and practically the total difference in head between head-water 

 and tail-water is useful. 



The speed of a reaction turbine can be varied not only by vari- 

 ation of the runner diameter but also, and very effectively, by 

 varying the bucket angle and the angle between the entrance 

 speed and the peripheral speed. Combining both these means it 

 is possible to vary the speed of a pressure turbine for a given head 

 and capacity in the ratio 6:1. 



Three different designs for reaction turbine runners are shown 

 in Figs. 104, 105, and 106. The first, Fig. 104, represents a low- 

 speed runner which would be used for relatively high heads and 

 relatively small quantities of water. The bucket angle j8 is less 



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