82 



mechanical device which varies in construction with the different manufac- 

 turers. Instead of using pressure gates, the ordinary slide gate can be used 

 by placing it on the downstream side or outlet to the box, but in this case 

 the box must be built so that its top is higher than the highest distributing 

 stand of the section. This may require a height of 10 or 15 feet above the 

 ground, which is objectionable. The pressure system can be used where 

 the distributing line has to cross shallow depressions. In all cases the line 

 must be divided into sections so that the maximum head will not exceed 



15 feet. 

 Details of stands. 



The stands are shown in detail in the accompanying diagram. Stand 

 A, used for the overflow system, consists of a section of 6 or 8 inch pipe 

 placed vertically with the lower end cut to saddle over a 6 or 8 inch hole 

 made in the pipe line by means of a sharp pick. The joint is made with 

 a rich cement mortar mixed in the proportion of 1 part of cement to 2 of 

 sand. Around the upper end of the pipe, at the surface of the ground, is 

 placed the distributing basin and the space in the basin around the smaller 

 pipe is filled with cement mortar. The basin is usually a section 6 to 18 

 inches long of 16 inch pipe. Around the circumference of the basin, near 

 the floor, from 4 to 6 distributing gates or spouts are inserted and cemented 

 in holes cut as soon as the basin has been made or cast in the basin when 

 making it in the metal moulds. 



Stand B is also used for the overflow system and consists of a single 

 length of pipe 8 to 12 inches in diameter in which the spouts are inserted. 

 (Fig. 69). The larger basins of the type A are preferable where the fur- 

 rows tend to wash together. 



Stands C and D are used for the pressure system. They are made as 

 stands A and B with the addition of the regulating valve cemented in the 

 upright pipe (Fig. 70). Stand E. can be used also for the pressure system. 

 It is similar to basin B with the top closed by a cap of cement mortar. This 

 stand requires that spouts be opened from the outside and unless they are 

 properly made, the pressure will cause them to leak. With the other stands 

 the spouts may open either from the outside or inside. 



Overflow stands. 



Overflow A is ordinarily made of a section of 16 inch pipe at the top of 

 which is cut an overflow notch 5 or 6 inches deep and 7 inches wide and 

 against this 16 inch pipe and cemented to it is a semi-circular or 2-3 cir- 

 cular section of an 8 inch pipe. The gate in the upstream compartment is 

 a simple slide gate. 



Overflow B consists of an overflow wall 2 inches thick built in a 14 or 



16 inch pipe. Overflow C is made of two stand pipes connected with a 

 short piece of 6 inch pipe. 



Draining the pipes. 



In order to empty the pipe to prevent bursting by freezing and also to 

 flush out any silt, it is necessary that at all the lowest points openings con- 

 trolled by valves or gates be provided. 



Accessories. 



The accessories needed for a pipe system are: (1) the galvanized iron 

 spouts, (2) regulating gates, which are either the simple cast iron or steel 

 slide gates or the pressure gates, (3) the valves. These devices are made 

 by several manufacturers in southern California and vary in detail. Prob- 



