SYPHONS 



275 



But 



y i PC' 



jf ~r -. 



1 + 



fl 



20 ( m 



= loss at exit -j- friction loss -f- loss at entrance* 



The assumption that both legs of the syphon 

 run full is one which is not always justified in 

 practice. Evidently the height B A must be 

 less than the barometric height by an amount 



-il -f- A ' B + K\ or we should have an 

 20 I m ) 



absolute vacuum formed at points below B, 

 and the flow would cease. Theoretically, the 

 limit of possible flow up the inlet leg is 

 reached when the pressure at the summit B 

 is absolute zero (34 feet of water), 1 and is 

 then given by the equation 



A 



I 

 i 



FIG. 123. 



Or writing K = '5 and Z A for Z^ + ?dl we 



20 



1-5 



the suffix (1) referring to the inlet leg. 



If the actual flow is less than this, p B is greater than zero, and we get 

 an additional head aiding the flow down the outlet leg. 



The velocity of flow down the outlet leg with maximum flow up the 

 inlet is given by the equation 



20m 

 the suffix (2) referring to this leg. 



If the syphon is to run full, we must have r a not greater than Vi 



1 Actually less than this, because of liberation of air at low pressures. 



T 2 



