106 



HYDRAULICS AND ITS APPLICATIONS 



greater than *598. The coefficient is the same for a given orifice under * 

 given head, whatever be the direction of discharge. The following tablei 

 give the essential results of these experiments : 



COEFFICIENTS OF DISCHARGE FOR STANDARD CIRCULAR ORIFICES. 



Head 



Diameter of Orifice in Inches. 



The critical heads and the corresponding normal coefficients are in bold figures. 



T. P. Strickland, 1 from experiments on sharp-edged orifices of 1 ind 



018 

 and 2 inches diameter, deduces the formula C = '5925 -\ / T 



V It - <l'-l 



where d is the diameter in inches and h the head in feet. 



With a rectangular orifice, the coefficient is rather greater than with c r 

 square orifice of the same area, and generally increases with the ratio o: 

 the perimeter to the area of an orifice. 



Suppressed Contraction. Any interference with the free production oj 

 stream lines, such as occurs, for example, where the depth of water above 

 the orifice is too small, or where this is near the sides or bottom of a tanls 



1 " Proc. Inst. C.E.," vol. 181, p. 531. 



