Practical preventive medicine . Fig. 37.—Sand washing machine, Indianapolis Water Company. Sand beingremoved from filter bed, washed and stored by hydraulic 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 ME
Practical preventive medicine . Fig. 37.—Sand washing machine, Indianapolis Water Company. Sand beingremoved from filter bed, washed and stored by hydraulic 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
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