Pressure sand filter

Filter is used for separating water suspended solid. For better operation of filter, suspended solid should be coagulated. The advantages of pressure filter are high speed of filtration, less space, low charge and prevent heat loss after the warm or hot lime process.  
  Karizab pressure filters, which may be vertical or horizontal, have cylindrical steel shells and dished heads. The flow in pressure filters is downward. Usually sand or anthracite is the filter medium in a bed consisting of either one or two grades of sand or anthracite. A gravel bed supports the filter medium, prevents fine sand or anthracite from passing into the underdrain system and distributes backwash water.  
   The water, which should be filtered, enters over the top of filter and pass from its bed then they collected at the bottom of filter. The suspended matter is strained out of the water and held in the voids between the filtering granules. The accumulation load of suspended matter in the bed causes an increasing loss of pressure during the filter run. When this loss reaches a predetermined limit, the filter is backwashed upward, discharging the suspended load out to the sewer.