454 



HYDRAULICS AND ITS APPLICATIONS 



water supplied through the small pipe P keeps the main escape valve V 

 closed so long as the valve V\ is closed. If this valve is opened, however, 

 by a sudden upward motion of L, the pressure above the main valve is 

 relieved, and the valve opens, relieving the pressure at the nozzles N N. 



The valve F 2 permits of a sudden depression of L, without unduly 

 stressing the dashpot rod A. 



A modification of the needle method of regulation is indicated in 



Scale of Lengths 



FIG. 205. Double Tangential Impulse Wheel, 500 H.P. at 375 Revolutions 



under 262 feet head ; wheel diameter 3-28 feet. The Kubel Electric Power 



Plant, St. Gall. 



Fig. 205, 1 which shows a section of a double tangential wheel of 3'28 feet 

 diameter developing 500 H.P. under a head of 262 feet. Here the nozzle 

 is rectangular in section, while its upper side is formed by a pivoted flap 

 whose position is regulated by that of the piston of a relay cylinder 

 actuated by the governor. The area of this piston is so large that when 

 its upper side is relieved of pressure, the upward pressure on its lower 



1 By courtesy of Messrs. Escher, Wyss & Cie., Zurich. 



