同燎大学 ③)ration WASH-WATER TROUGH FILTER TANK 24-301N. SAND SURFACE WASH 10-12 IN.GRAVEL PRECAST FILTER BOX FLOW DURING BACKWASH FILTERED WATER (WATER TO WASTE) FLOW DURING FILTRATION FLOW (RAW WATER) DURING BACKWASH Fig.3 Typical gravity rapid rate filter systemTongji University (3) Rapid filtration Fig.3 Typical gravity rapid rate filter system