368 



VETEEINAEY HYGIENE 



error to put down a larger pipe than necessary, as the 

 solid contents get left behind ; within reason the smaller 

 the pipe the better the flushing. 



The gradient given to a drain is a very important matter, 

 if too steep the water runs off and leaves the solids behind, 

 if too shallow the drain is insufficiently emptied. 



Fig. 154. — Access Pipe. 



The gradient depends upon the diameter of the pipes, 

 the smaller the pipe the steeper the gradient ; what the 

 sanitary engineer aims at is a continuous flow throughout 

 the entire system of between 3 and 4 feet per second. In 

 the case of a 4-inch pipe this is secured by a gradient of 

 1 in 40, of a 6-inch pipe by one of 1 in 60, of a 9-inch pipe 

 by one of 1 in 90. 



Kg 155.— Single 

 Junction, with 

 Diminishing 

 Pipe. 



Fig. 156.— A Bend 



A pipe must always open into one larger than itself, 

 a diminishing pipe being employed on the larger drain to 

 enable the junction to be effected (Eig. 165). 



Junctions are very important points to inspect, the joints 

 are frequently defective, or from want of a diminishing 

 pipe are made to offend against one of the cardinal rules of 

 drainage. 



Digitized by Microsoft® 



