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| Commercial Filter Manual
BACKWASHING
The function of backwashing is to separate the deposited particles from the filter media grains and
flush them from the filter bed. Backwashing is achieved by reversing the flow of water through the
filter bed at a fairly high flow rate. This high flow rate expands the filter bed and the water flow
carries the debris out to waste.
CONDITIONS FOR BACKWASHING
Time for backwashing is determined by the following conditions:
1.
The flow rate through the filter bed decreases until it is insufficient to meet the demand
2. The removal efficiency of the filter bed decreases to the point where filter water quality
deteriorates or results in dirt or debris passing through the system
3. When the pressure is between 50 to 70 kPa or 7 to 10 psi higher than the start-up pressure
4. If the differential pressure required to trigger a backwash is not achieved, a backwash should
be performed at regular intervals to prevent media solidifying or channelling.
5. If the filter is connected to mains water, pressure rise is not an accurate indicator as mains
pressure tends to fluctuate. It is best to rely on the actual flow rate or a predetermined time.
IMPORTANCE OF BACKWASHING
The importance of backwashing cannot be overstated. Dense filter media can become “packed”
without proper and frequent enough backwashing. Debris will remain trapped and create channelling
within the filter bed. This will result in the filter bed exhausting early. If debris is not flushed from
the media grains, the filter bed will become blocked as time goes on until the filter operation fails.