334 MODERN METHODS OF WATER PURIFICATION. 



The water inlet to each filter is a funnel set in the masonry. 

 This funnel opens into a gutter running round three sides of 

 the filter and across the centre. These gutters are used to 

 distribute the water to be filtered and also to remove the filter 

 wash water. 



The strainer system is in the floor of the filter. The strainers 

 are little brass perforated cylinders, or cups, of the pattern 

 known as the Jewell continental ; these are screwed into a 

 cast-iron oval pipe 12 by 6 inches running the length of 

 the filter tank in the centre, and they are also screwed into 

 lateral pipes connected to this header at one end, and extend- 

 ing to the side of the tank with the other, which is plugged. 

 The neck of the strainer is a f inch brass tube, which extends 

 into the lateral tube, which is if inch diameter to within f inch 

 of the bottom, i.e., lower side of the pipe. This extension 

 of the neck of the strainer forms a trap, when (as will be 

 described later) air, under pressure, is driven into the filter in 

 order to agitate the sand. This air, like the wash water, 

 enters in the reverse direction from that of the filter water flow, 

 as will be understood from its use, and the air passes from 

 the lateral tube into the strainer through a small perforation 

 in the neck of the strainer just below the upper wall of the 

 lateral tube. The body of the strainer is made of hard cast 

 brass, and the top of this is a cupped brass plate perforated 

 with a number of holes, as also on the sides; in the Little Falls' 

 plant, each of these strainers has 33 holes, but the number of 

 perforations varies and also the size of the perforation, e.g., 

 the Warren filter has larger holes than the Jewell. 



An idea of the closeness of the setting of these perforated 

 brass strainers can be gathered from the estimation that there 

 are over 13,000 of such strainers in the floor of a filter tank about 

 the size of a fairly large dining-room — 360 feet area ; they are 

 screwed into the pipe which gathers the filtered water, and 

 stick up about an inch above the floor of the filter. The size 

 of the holes in these strainers of the Jewell continental type is 

 i-i6th of an inch diameter. The strainers look like brass spin- 

 ning tops or brass egg cups covered over with a perforated 

 brass disc, but at the pointed end of the inverted cone is a 

 screwed stem which is the part screwed into the pipes, header and 

 laterals. They are one to two inches in diameter, and, look- 

 ing down on them when they are screwed into position, they 

 look like perforated brass discs, through which the filtered 

 water runs downwards and the wash water runs upwards. As 

 these mechanical strainers have holes too big to support sand 

 resting directly on them there is broken quartz round and over 

 them. The quartz is coarser for the bottom two inches and 

 finer above for five inches; the quartz supports the sand of 

 the filter. In the Columbus installation, which is more recent 

 than the Little Falls, the lateral waterways are channels in 

 the concrete floor of the filter. Over these are. placed 

 " strainer slabs," containing the strainers themselves, which 

 in this particular installation are perforated brass discs with 



The perforated brass strainers have not only the one func- 

 tion of giving passage downwards to the filtered water, they 

 i-i6th inch holes. 



