218 



SEWER DESIGN 



limb, at which time the water is depressed in the blow-off trap 

 to the lowest point and the confined air breaks through the 

 seal, carrying the water with it out of the trap, thus releasing 



FIG. 63. 



the confined air and allowing an inflow from the tank, putting 

 the siphon into operation. 



" On the tank being discharged to the bottom of the intak- 

 ing limb the flow is checked, and the siphon is vented by the 

 admission of air to it through the vent-pipe." 



