SMALL ORIFICES 



105 



Circular Orifices; diameters in feet. 



Smith's " Hydraulics," indicates the nature of these variations. In each 

 case the orifice had full contraction, had free discharge into air, and the 

 inner face of the plate in which the orifice was formed had sharp corners, 

 so that the escaping jet only touched these inner edges. 



More recent experiments throw some doubt on the assumption, based 

 chiefly on the work of Smith, that the coefficient decreases up to a head 

 of 100 feet, under which head it has a constant value of '592 for all 

 diameters from *5 inches to 12 inches. Among these may be quoted 

 those of Messrs. Judd and King at the Ohio State University, 1 which 

 were carried out on orifices of diameters J inch, 1 inch, 1J inches, 

 2 inches, 2j inches, under heads varying from 4 to 93 feet. The 

 results showed a very small change in the coefficient for an increase of 

 head. The following are from tests on the 2-inch orifice : 



Experiments by H. J. Bilton 2 indicate that if an orifice is less than 

 about 2'5 inches diameter perfect contraction is impossible, the degree 

 of imperfection becoming more marked as the diameter decreases. This 

 is true however high the head. For orifices of greater diameters the con- 

 traction appears to be complete and constant for heads above about 17 

 inches, attaining a value '598. Smaller orifices likewise have a " critical " 

 head, greater than 17 inches, above which the contraction is constant but 



1 Engineering Neivs, New York, September 27, 1906. 



2 Engineer, June 19, 1908. 



