448 



HYDRAULICS AND ITS APPLICATIONS 



(1) The stream may be deflected so as to partially miss the buckets at 

 part load, either by swivelling the nozzle, which is then carried on a ball- 

 and-socket joint, or by a stream deflector placed between the nozzle and 

 the wheel. In the former case, owing to the friction at the swivelling 

 joint a considerable force is required to deflect the nozzle, and in conse- 

 quence the governor must be fitted with a hydraulic relay cylinder, as at 

 C (Fig. 207). The piston rod of this cylinder carries the nozzle, and the 



governor by regulating 

 the supply of pressure 

 water to one side or 

 other of this piston, also 

 regulates the position of 

 the nozzle. 



This method of regu- 

 lation has the disadvan- 

 tage of being wasteful 

 of energy at part load, 

 while the nuisance 

 caused by the discharge 

 of the jet directly into 

 ihe wheel pit may be 

 very great. 



On the Pacific slopes, 

 however, many of the 

 water companies require 

 that a constant flow 

 through the pipes be 

 maintained, in order that a constant supply may be delivered over a weir 

 to a ditch of lower level, and in this case the deflecting nozzle affords 

 the most suitable means of speed regulation. The method possesses a 

 further advantage in that it avoids all action of the nature of water ram 

 in the pipes. 



(2) The velocity of the jet may be reduced by means of a throttle 

 valve placed behind the nozzle This is not to be recommended, since 

 the contraction and subsequent enlargement of the stream which occurs 

 at the valve is wasteful of energy, while the variation in the velocity of 

 the jet tends to inefficiency in working. 



Further, since the sudden closing of the valve causes a corresponding 

 increase of pressure throughout the pipe due to water hammer (p. 222), 

 this method of governing should never be adopted without the addition of 



FIG. 200. 



