NOZZLES 281 



ditions, certainly within 1 per cent., these nozzles are very satisfactory 

 for such a purpose, this accuracy being quite as high as that attending 

 the use of a standard weir for measuring purposes. 



The form of nozzle used in connection with the Pelton wheel is dis- 

 cussed in Arts. 125 and 126. 



Velocity of Plow through a Nozzle. 



Let A, L, and V A refer to the supply pipe, and a and v a to the nozzle 



rlvu r A a 

 Then -^ : -r. 

 * a A 

 If H = supply head in feet we have 



2<i 2 g m 2 # 2 g 



where K and k represent the coefficients of loss at the entrance to the 

 pipe and at the nozzle. 



Putting V A = v n .~ we get 



A 



( A ' mA* j 2# 



* . . . . 



. * . V a = V ~ 77 2 W 



Since k = "05 (approximately), while K 2- is in general small, neglect- 



A 



ing these terms we get 



/ 2# H I 2g H 



^ . j I a 1 i 4 / t a 



^4^ "IF- 



If ^ = pressure in pounds per square inch at the entrance to the 



k T 2 



nozzle and if T - = loss in nozzle 

 %9 



4 ^^3- (3) 



This formula may be used to determine k t and hence the coefficient of 

 velocity V (1 k), by measurement of _p and of the quantity discharged. 



