SEWAGE DISPOSAL 41 



pipes to be cut. This may be accomplished by using Ts or 

 double Ts instead of Ls, closing them with plugs. 



Sewer Traps. A sewer trap is a contrivance holding water, 

 to be placed in local drainpipes wherever there is danger of air 

 from a sewer getting into the interior of a building. The water 

 acts as a seal against passage of gas in either direction, but 

 permits free passage of liquid in the direction of the main sewer. 

 The principal kinds of traps used in a creamery are the bell 

 trap, the siphon trap, and the S trap. 



i. Bell Trap. This is the one most commonly used in 

 smaller creameries. In large creameries, the bell trap is often 



FIG. 6. Bell trap. 



used as a floor trap, while one of the other forms may be added 

 to the sewer system. The bell trap alone usually affords suffi- 

 cient protection in small plants when a comparatively large 

 amount of water is passing through at short intervals and where 

 the creamery sewer is not connected with some larger sewer 

 system as in cities. A bell trap cannot be ventilated; therefore, 

 whenever that is found necessary, another style of trap should 

 be installed. 



The principal reasons of insufficiency in a non- ventilated trap 

 are: 



i. An increased pressure of gas within the sewer may displace 



