Chicago South District Filtration Plant

now attracting attention, the most important of which is the operation of filters at high rates. This was made possible by the development of means of toughening coagulation at the experimental filtration plant in 1937. In the new plant, ten of the 80 filters are being operated at rates of 4-5 gpm. per square foot. This experience is paving the way to setting a figure of 3 gpm. as the rated capacity of rapid sand filters. Figure 1 is a general layout of the plant, showing the relation of the filters to other parts of the plant. A section through one of the filter galleries and two filters is illustrated in Fig. 2. A number of items of filter design differ from the usual practice: [1] The sand level is 7.7 ft. below average water level on the filters; [2] the filter manifolds are of concrete and are larger in size than those generally used ; [3] the filter rate controllers have Venturi tubes of special design with a long recovery cone and one butterfly valve; [4] a pneumatic telemetering system is used to actuate the rate-of-flow, loss-of-head and sand expansion gages located on the operating table; [5] the underside of each wash water trough is flat and level, so that it is a uniform distance above the sand; [6] the filters are provided with surface wash systems of fixedjet type; [7] sand expansion devices record on a chart the expansion during backwashing; [8] steel fourway plug valves are used on the operating table manifolds ; [9] flexible shafts are used instead of cables to transmit