SYPHONS 



277 



height, the distance of the syphon below A f C' will give the absolute 

 pressure at any point. In the sketch, syphons A BI C, A B 3 C, and 

 A B 2 C are shown connecting A and C, all rising to the same height It, 

 above the surface at A. Here, although 7? 2 is not nearly 34 feet above 

 A, an absolute vacuum would be attained before reaching 7? 2 >ind the 

 syphon will consequently not work. A comparison of Q and0 shows 

 that there is a greater pressure in the air vessel at BI than at B 3 , and 

 the syphon Q will thus run longer without removal of air from this 



FIG. 124. 



chamber than will f$). Leakage at joints is not likely to have so serious 

 an effect as with . 



Any accumulation or air at the highest part of the pipe LAS the effect 

 of increasing the pressure, and hence of lowering the line A' B f . Directly 

 this line is lowered sufficiently to cut the pipe line the syphon ceases to 

 flow. The air vessel should always be placed at the point of least 

 pressure, i.e., at the point nearest to the hydraulic gradient line A' C'. 



If A' A" = C' C" = , the line A" C" will give the hydraulic gradient 



() 



taking into account change of potential into kinetic energy at the 

 entrance to the pipe. The effect of this is to reduce the value of the 

 ratio A B : B C, for both branches of the syphon to run full with 



