214 SEWER DESIGN 



a sudden discharge through a gate or other device. This may 

 be done either automatically, or by hand; at fixed intervals, 

 or whenever deemed necessary. In this country a reservoir 

 accumulating water from the public water-supply and discharg- 

 ing through an automatic gate (the so-called automatic flush- 

 tank) is the flushing method in general use. In many cases, 

 however, it would seem a sad lack of judgment to neglect to 

 provide, when it can be easily and cheaply done, other means 

 of washing out the mains and laterals of a system. 



When hand-gates are used, limited, on account of weight, 

 to pipes of about 20 inches diameter, either the water-supply 

 or sewage may be used. For this purpose the brickwork on the 

 lower side of the manhole beyond which it is suspected that 

 deposits may occur is brought up in a plane around the pipe 

 from the bottom, and a bearing-surface for the gate bolted on; 

 or a frame in which the gate may slide up and down may be 

 secured to the manhole wall. The end of the pipe may form 

 the bearing-surface, or the pipe may be closed by a plug. 



Large sewers, especially storm-water sewers in which the 

 flow-volume varies largely, require gates too large and heavy 

 to be raised directly by hand, and a screw or windlass must be 

 provided. If such a gate is located at a point in the sewer 

 where an overflow into some stream can be arranged, it provides 

 for the contingency of a gate sticking or broken mechanism or 

 the negligence of attendants. 



Automatic flush-tanks, generally used with 6- and 8-inch 

 sewers, in this country are of two types, viz., operating through 

 some movable part or through the starting up of a large siphon. 

 Of the first type is that made in Schenectady, N. Y., by the Van 

 Vranken Flush- tank Co., the following description and drawing 

 of which is taken from the circular (see Fig. 61): 



" The tank consists of a siphon, of which the interior diam- 

 eter ranges from 5 to 8 inches in the various sizes, a trap at the 

 bottom, and a cast-iron case connected with the sewer or drain. 

 It is this trap that forms the essential feature of the Van Vranken 

 siphon. Instead of being fixed, it is hung on trunnions under 



