634 



HYDKAULICS AND ITS APPLICATIONS 



Whirlpool Chamber. In the arrangement of collecting chamber suggested 

 by Professor James Thomson and known as the vortex or whirlpool 

 chamber, the impeller is surrounded by a casing which may be looked 

 upon as a volute chamber of uniformly increasing area superposed upon 

 a circular chamber concentric with and of considerably larger diameter 

 than the wheel. Fig. 303 shows such a vortex chamber. In the concen- 

 tric portion of the casing, the water on leaving the wheel is free to adopt 

 its own manner of motion which approximates to that of a free vortex. In 

 this vortex the pressure increases outwards, theoretically following the 



FIG. 303. 



ordinary free vortex law. Uniform discharge then takes place around the 

 circumference of the vortex chamber, through the gradually increasing 

 volute passage. The great drawback to this device is that to get a very 

 efficient chamber, the dimensions become excessive the efficiency increas- 

 ing with the radius and, in consequence, it is seldom adopted save in a 

 modified form. In this form it is very general. 



Even with this chamber, however, the efficiency of transformation is 

 greatly diminished owing to the instability of diverging motion and the 

 consequent loss of head in eddy formation, and the efficiency actually 

 obtained does not in general exceed about 40 per cent, of the theoretical. 



Guide Vanes. The tendency to instability of motion and the hea 

 losses due to shock may be largely prevented by the introduction of fix 



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