PELTON WHEEL 



455 



face, which is in communication with the nozzle, is sufficient to close the 

 flap. Pressure water from the nozzle is supplied to the regulating valve V 

 (Fig. 206) which regulates the pressure on the top of piston P. If the speed 

 of the wheel increases the governor sleeve rises and the lever A C turns 

 about the fulcrum B, depressing valve V and putting the upper side of 

 piston P into communication with the exhaust. This piston rises, closing 

 the nozzle, and also lifting the point of attachment F of the link F B. 

 This raises B and also C and brings the valve V into a new position of 

 equilibrium, in which it is prepared to take control of any fresh change of 

 speed. A striking feature of this installation is that it is fitted with a 

 draught tube (Art. 134), 

 and works under a suc- 

 tion head of 22 feet. 



(4) A modern and 

 very common method 

 of regulation is illus- 

 trated in Fig. 207. 

 Here a combination 

 needle and deflecting 

 nozzle is used, the 

 needle being set by 

 hand, so as to 'take the 

 maximum load likely to 

 occur during any hour, 

 while the deflection 

 takes care of any varia- 

 tion of load up to this 

 peak. With a very 

 variable load, such as 

 occurs in electric light- FIG. 206. 



ing plants, considerable 



economy may thus be effected, while the possibility of water ram if 

 eliminated. 



A self-regulating wheel which has been tried with good results as regards 

 speed regulation consists of two discs mounted side by side on the same 

 shaft and capable of relative sidelong motion. These are kept in position 

 by springs, and each carries a series of half buckets which fit together 

 when the discs are close together and then form ordinary Pelton buckets. 

 An increase in speed, by the consequent increased centrifugal force on 

 masses mounted on bell- crank levers connected to the wheel, produces a 



Exhaust 



Pressure 



Link to flap 



