238 



SEWER DESIGN 



On Buffalo Street, where the grade is about 12 per cent, 

 the effective of the flush was amazing. Where any sewage 

 at all flows in the pipe, it is sufficient to remove all obstruc- 

 tions. A flush of any volume rushes down the hill at a 

 high velocity, with piston-like action, and sweeps everything 

 before it. 



Table XXXI gives the distances and grades between man- 

 holes on the lines used in the experiments. 



TABLE XXXI 



DISTANCES AND SLOPES BETWEEN MANHOLES 



The manager of the Van Vranken Flush-tank Company 

 gives his practice in proportioning the sizes of flush-tanks 

 for any particular sewer as follows: The capacity of the reser- 

 voir should be equal to one-half that of a length of sewer in 

 which the grade produces a rise equal to the diameter of the 

 pipe; so that the Green Street line, 8 inches diameter and 

 0.5 per cent grade, should have a discharge of half the volume 

 of the pipe, fXioo in length, or 23 cubic feet; and for a i per 

 cent grade one-half of that, or 11.5 cubic feet. He says, further, 

 and the statement has been confirmed by the author's work, 



