. ONTARIO SESSIONAL PAPERS, 1914, the gravel, and to examine thesand strainers, whicli were the Hodkinsoii type of sand valve and v8 in numberat the bottom of the filter. After the sand and gravel had been removed, exposing the strainers, the washwater wa3 turned on. H then became evident that some of the trouble was located,for while a portion of the strainers emitted water, others did not; and practicallynone of the strainers distributed it freely. An examination of the strainersdisclosed the fact that sand had clogged them, not externally (filter side) as hadbeen expected, but int
. ONTARIO SESSIONAL PAPERS, 1914, the gravel, and to examine thesand strainers, whicli were the Hodkinsoii type of sand valve and v8 in numberat the bottom of the filter. After the sand and gravel had been removed, exposing the strainers, the washwater wa3 turned on. H then became evident that some of the trouble was located,for while a portion of the strainers emitted water, others did not; and practicallynone of the strainers distributed it freely. An examination of the strainersdisclosed the fact that sand had clogged them, not externally (filter side) as hadbeen expected, but internally. The cause of the trouble arose from the wash-waterand was due to sand present in the city mains. In operating the reverse-flow tothe filter, the water had driven the sand into these strainers with such forcethat when the filter was put into operation, the pressure in the filter being slight(about .5 pounds compared with 40 pounds in the reverse-flow) the pressure was COMPARISON BETW EEN WATER LEVEL IN FILTER AND LOSS OF HEADMar 9^. 2 3 Time in Hours not sufficiently great to dislodge the sand. As a result, the available head at theeffluent pipe of the filter gradually became less and less as more and more sand wascompacted into the strainers. All the strainers were removed and thoroughly cleaned by hand and with the gravel and sand restored, (the copper wire gauze now being omitted)the filter was started afresh. With these alterations the head at the effluent increased from 3 feet, whichexisted after tTie wire gauze was taken out, to 6 feet 6 inches. Ordinarily sand will not be found in the wash water when filtered water isused, but in cases where it might ofcur (as it did at the Experimental Station)measures should be taken to entrap the sand instead of allowino- it to collect and 132 THE EEPORT OF THE No. 31 COMPARISON BETWEEN WATER LEVEL IN FILTER AND LOSS OF HEADMar 10/- I \J,C,^ yV(.».r , 1 \l He iqbt of F Itering N toss of ^cod Corvz / Ttni
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