TURBINES 



245 



Referring again to Fig. 116, a water connection for throwing a 

 fine spray of water through the hollow shaft will be noted on the 

 outer end of the right bearing. Within the housing of a tangential 

 wheel there is a very definite vacuum due to the action of the 

 revolving wheel as a centrifugal blower and the action of the jet 

 of water acting as an injector. Therefore discharging a fine spray 

 of water into the open end of the shaft, this is drawn through and 

 is most effective in cooling. 



The illustration (Fig. 116), also shows what is termed a " tail- 

 race ventilator." This is a labyrinth passage from the bottom of 



FIG. 135. Impulse Turbine with Two Nozzles per Wheel. Arranged with 



Auxiliary Relief. 



the generator pit to the water-wheel pit, tne vacuum existing in 

 the water-wheel pit bringing about a very definite circulation of 

 air which it draws out of the bottom of the generator pit. 



The three principal types of nozzles used with impulse tur- 

 bines were described under " Speed Regulation," page 221. 

 While one jet per wheel is used in most cases, there may be installa- 

 tions where the head of water available is low, as compared with 

 the quantity of water and where it is desired to maintain a com- 

 paratively high speed of rotation. Under such conditions two 

 jets of water may be applied to each wheel from the same nozzle 



