376 



HYDRAULICS 



would also be the same if the reservoir were deepened and the 

 pipe laid along the line a'd'f. The pressures in the pipe, 

 however, would vary greatly with the different positions. If 

 the pipe were laid along the line adfg, there would be little or no 

 pressure in any part of it. In the horizontal position, however, 



and still more in the position a'd'f, there would be pressure 

 at all points, the pressure for any point in the pipe being 

 equivalent to the head represented by the vertical distance 

 from that point to the hydraulic grade line. 



Position of Hydraulic Grade Line. In laying a line of pipe 

 to connect two points lying at different levels, it is of the 

 utmost importance to ascertain the position of the hydraulic 

 grade line. In order that the pipe may flow full, no part of it 

 should rise above the hydraulic grade line. 



The Siphon. The part of a pipe that rises above the hydrau- 

 lic gradient is called a siphon. If the siphon is kept filled, the 

 flow through it will take place in accordance with the laws given 

 for pipes laid below the hydraulic gradient, and the same for- 

 mulas apply." 



The total head producing the flow in a siphon is the ver- 

 tical distance from the discharge end of the pipe to the level 

 of the water in the reservoir, but the pressure in all parts of 





