This Table assumes that you have already determined the plant flow required for a specific application. It also assumes that you have decided to use a shunt backwash method. In conjunction with a suitable filter rate (in m3/hr/m2) look for the flow rate that you have selected keeping in mind that the most cost effective selection will have the fewest number of filter vessels


  1. By using the minimum plant capacity filter rates as low as < 8.5m3/hr/m2 may be provided.
  2. 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.
  3. To prevent preferential flow, the filter modules in a shunt backwash system should be backwashed sequentially. Extend the washwater consumption/filter to account for the total number of filters. Determine the size/capacity of the backwash detention tank, sludge lagoon, or washwater recovery system by making adequate allowances for plant over-run, freeboard, and accumulation of sludge.
  4. Minimum plant flow is based on the filter’s required backwash flow multiplied by 1.2. This ensures that the shunt backwash valve does not need to be fully closed to obtain the required backwash rate.
  5. Maximum plant flow is based on the number of filters minus one, times the filter area of one module, times 42.