IMPROVEMENTS RELATING TO FILTRATION

1519821 Filtering water SEA WATER SUPPLIES Ltd 10 Feb 1976 [18 Feb 1975] 6717/75 Heading B1D [Also in Division El] Sea water or fresh water standing or flowing over a natural sand or gravel bed is extracted through outlet 12 of an open-bottomed box 2 bridged by an upward-flow slotted plate 6, the box being partly or wholly buried so that plate 6 rests either on the natural surface of the sand or gravel or on a surface thereof below said natural surface. The sand or gravel thus filters the water, plate 6 excluding sand or gravel from outlet chamber 7. Chamber 7 is divided into square interconnecting chambers 8 by two sets of crossing walls 9, the slots in plate 6 being similarly divided into groups (Fig. 2 not shown). The slots diverge upwards (Fig. 3 not shown). When the box is. initially buried, the downstream pump is operated intermittently to establish a stable filter bed beneath plate 6 and thereafter runs continuously. The box is made of glass fibrereinforced plastics.