100 



SMALL WATER SUPPLIES. 



air pockets or summits, and this gradient should not 

 k be less than 1-150. 



~ WbodsTUbe lt is equally im- 

 portant to see that 

 the pipe joints are 

 quite tight, or else 

 air will leak in 

 and stop the pump 

 working. It should 

 always be tested 

 to about 30 Ib. per 

 sq. in. before fill- 

 ing in the trench 

 it is laid in. Cast- 

 iron flange pipes 

 are the best, or 



FIG. 81. 



spigot and socket pipes laid downwards from the 

 pump. Valves on either suction or delivery should 

 be full-way gate valves, while the merits of the foot 

 valve have already been discussed, but the strainer, 

 which is usually combined with the foot valve, must 

 always be specified to have openings to a total area 

 at least four times that of the suction pipe so as to 

 reduce friction. The strainer also should be fre- 

 quently examined and cleaned if required, a precau- 

 tion too often overlooked. 



Finally, when the suction pipe is fitted the utmost 

 care must be taken to see that there is no foreign 

 matter in it of the smallest degree which would get 

 into the pump and do certain damage. The dis- 

 charge pipe would be laid in the same way as will 

 be described in the next chapter, with the simple 

 addition of a relief valve immediately next to the 



