276 HYDRAULICS AND ITS APPLICATIONS 



M-(Z B -Z A )" 1-5 

 If the syphon ho long, so that 1'5 m may be neglected in comparison 

 with//! we have 



(Z B - Z c ) - 34 ^ k 

 34 - (Z B - Z A ) * /i 



or 



34 - (Z B - 

 . k^U- 

 ' 1 * (Z A - 



f 

 If 



EXAMPLE. 



Z A Z c 50ft. 

 I = 1,000 ft. 



z*-z x = 10 ft. 



1,000 X 24 



-~ 



or the outlet leg will not run full if the inlet leg is more than 480 feet 

 in length. 



With a longer inlet and shorter outlet the flow up the inlet will not be 

 able to keep pace with that down the outlet, and this will then run only 

 partly full. Also the velocity up the inlet will not now be so great as 

 with a shorter inlet, so that the discharge will be less. Evidently, then, 

 the position of the apex of the syphon has a great influence on the 

 discharge. 



With a shorter inlet and a longer outlet, the total length being the 

 same, the discharge will be unaltered, but the syphon will have the 

 advantage of working under a greater absolute pressure at the apex, and 

 is therefore less likely to be affected by air leakage at the joints. 



In practice it is necessary to place an air chamber at the highest point 

 of the syphon, into which air gradually accumulates during its working. 

 This air is then removed at frequent intervals, either by some form of 

 air pump, or by means of a steam ejector. 



Where the syphon discharges into the atmosphere, any failure of the 

 outlet leg to run full, by admitting air to the apex at once breaks the 

 vacuum and stops the flow. 



Figure 124 shows the hydraulic gradient for a syphon, the straight line 

 A C being the gradient line. In drawing this the only losses taken into 

 account have been those due k> friction. If a second line A' C' be drawn 

 parallel to and at a vertical distance from A C equal to the barometric 



