460 



HYDRAULICS AND ITS APPLICATIONS 



and a Pelton wheel nozzle with needle regulator. 1 From these it appears 

 that the central velocity at a point distant J inch from the tip of the needle 

 is only '68 of the maximum velocity. At a section 3J inches from the tip 

 this ratio becomes 1 90, while when the distance is 9^ inches it becomes *96. 

 At mid opening (diameter 1*25 inches) the coefficient of 'velocity dimi- 

 nishes slightly as the head increases, from about '992 with 23 feet head to 

 978 with 120 feet head. With a given head the velocity was slightly the 



POSITIOHS OF NffOtC * TIP DUUIHS 

 MEASUREMENT OF HOZZLC OPENINCS. 



FIG. 209. 



greatest with the nozzle half open. The efficiencies in these experiments 

 varied from '964 to '993. The maximum jet diameter was 1*50 inches. 



Experiments on a larger nozzle, giving a jet up to 7 inches diameter 

 under heads up to 850 feet, 2 showed the following results : 



1 From a Thesis by H. C. Crowell and G. C. Lenthe (Massachusetts Institute of 

 Technology, 1903). 

 a W. R. Eckhart, Inst. Mech. Engineers, January, 1910. 



