Sewage disposal . thus formed should be inclined downstream andshould make an angle of about 30 degrees with the vertical (seeFig. 25.) Bar screens may readily be cleaned by means of hand rakes,the teeth of which fit into the spaces between the bars or it is necessary to place the screen much below the groundlevel, it can be cleaned by a long-handled rake; or the screenitself may be lifted to the surface for cleaning by means ofpulleys operated by hand or power. In some large plants, as atBoston (see Fig. 11), the bars form the sides of a cage with a 68 SCREENING AND STRAINING OF SEWAG
Sewage disposal . thus formed should be inclined downstream andshould make an angle of about 30 degrees with the vertical (seeFig. 25.) Bar screens may readily be cleaned by means of hand rakes,the teeth of which fit into the spaces between the bars or it is necessary to place the screen much below the groundlevel, it can be cleaned by a long-handled rake; or the screenitself may be lifted to the surface for cleaning by means ofpulleys operated by hand or power. In some large plants, as atBoston (see Fig. 11), the bars form the sides of a cage with a 68 SCREENING AND STRAINING OF SEWAGE perforated bottom, the whole cage being raised by power to anoperating floor where it is cleaned by hand. The usual open space for the bar type of screens is \ to 1 inchor more. Data for a number of Massachusetts screening plants,cited in the table on page 83, give a fair indication of NewEngland practice at intermittent sand filter plants, but thescreens listed are smaller than those generally used elsewhere in. Fig. 11. Cage Screen at Boston, Mass.(Courtesy of T. F. Bowes.) the United States. At Columbus, Ohio, there are three sets ofscreens, the first of 3 by f-inch bars set 6 inches in the clear, thesecond of f-inch rods 1 inch in the clear, and the third of f-inchrods, \ inch in the clear. At Washington, Pa., there are twosets of bar screens 4 feet by 3 feet outside dimensions, the firstset having an open space of f inch and the second set a space of\ inch. These screens need cleaning every hour or so duringthe day when the sewage is strongest, but only once in three orfour hours during the night. It has not been necessary to em- BAR SCREENS CLEANED BY RAKES OR BRUSHES 69 ploy any additional attendant to do this work, however, and theadvantage derived from using screens with so small an openspace is very marked. At the Dorchester plant of the SouthMetropolitan District of Boston two sets of bars are set oneinch apart so that the bars of one set correspond to the openings
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisherlondo, bookyear1919
