Practical preventive medicine . Fig. 38.—Mechanical filters at Chattanooga, Tenn. Note the vertical shaftsat the top of each pressure filter unit. To these shafts are connected the revolv-ing rakes which agitate the sand when the filter is washed. The shafting re-volves the rakes. It is because of these connections that pressure filters aresometimes called mechanical filters. (Courtesy of American Water Works andGuarantee Company.) 140 PRACTICAL PREVENTIVE MEDICINE. Pig. 39. -Schematic view of a typical rapid sand filter of the pressure type.(Mason, Water Supply, John Wiley and Sons.)

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Keywords: ., bookcentury1900, bookdecade1920, booksubjectprevent, bookyear1920