This table assumes that you have determined the plant flow required for a specific application. It also assumes that you have decided to use a tandem backwash system, with two filters arranged in parallel to “filter” at a flow rate of 21m3/hr/m2. In this case, the filters are individually backwashed with the full duty of the pump to achieve the required backwash rate of 42m3/hr/m2.


  1. The nominated backwash flow (in l/sec) is based on a backwash rate of 42m3/hr/m2. Subject to the type of filter media being used, this rate may vary.
  2. Pumping equipment should be selected to provide the required “backwash flow”.
  3. Filters with up to 3.5m2 of filter area may use single lever multiport valves; larger systems use commercially available valves arranged as either, a four or five valve matrix
  4. Larger plant capacities can be satisfied by using a number of tandem systems. Alternatively, a multiple tank system using a shunt backwash method may be considered