HYDRAULIC MACHINERY, FOR MINES 



839 



The velocity of a fluid spouting through an opening in the side of a vessel is the 

 same that a body would acquire by falling through a perpendicular space equal to 

 that between the top of the water and the middle of the aperture. 



KUI^E. Multiply the space in feet by 64-33, and the square root of the product 

 will be the velocity acquired in feet per second. 



Example. What is the velocity of a stream per second, issuing from a head of 10 

 feet ? 



VlOx 64-33 = 25'36 feet. 



If the velocity be 70 feet per second, what is the head? 

 70 2 -5-64-33 = 76^ feet. 



^ The "theoretical velocity with which a liquid issues from an orifice in the bottom or 

 side of a vessel that is kept full, is eight times the square root of the head or distance 

 fallen in feet. The practical velocity estimated for the entire opening is considerably 

 less than the theoretical velocity, owing to oblique currents and to friction. These 

 oblique currents produce a contraction in the vein or stream. The minimum trans- 

 verse section of the contracted vein is the plane at which the velocity is nearly equal 

 to the theoretical velocity. The quantity of water which will be discharged in a 

 certain time depends upon the form of the opening, as well as upon the head. Thus, 

 by means of a conical tube of the form of the contracted vein, the velocity at the 

 opening, or smaller end of the tube, is nearly equal to the theoretical velocity. The 

 actual velocity estimated for the entire opening, when constructed as ordinarily, and 

 not large, is 5-4 times the square root of the head in feet. 



TABLE III. Showing the relative velocities with which water, under a constant head, 

 will flow through differently-formed apertures : 



Theoretical velocity 8' 



Velocity through a thin plate 5- 



Velocity through a tube two or three diameters in length projecting outward . 6-5 

 Velocity through a tube of the same length, projecting inward .... 5-45 

 Velocity through a conical tube of the form of the contracted vein . . .7-9 



TABJ.E IV. Table for estimating the velocity with which water will flow under 

 a given head. 



