5.8.
Pressure Filter backwash procedure
Pressure filters may be in a single of multi filter manifold arrangement; there may be one or more pumps
that could be fitted with frequency invertors. Due to the multitude of potential configurations the
backwash procedure detailed below is a simple generic procedure that applies to all pressure sand filters.
1. Place the filter into backwash mode.
2. If the filter is to be air purged, drop the water level to a point just above the filter bed.
3. Turn on the air blower, pass clean air through the filter bed at a velocity of 55m/hr for a period of
3 minutes, turn off air blower and isolate air blower from the filter.
4. Turn on backwash pump and slowly build up the water velocity over a period of at least 30
seconds to the required flow rate at detailed in Table 3. If the filter has a viewing window check
that the bed raises evenly and that bed expansion is 20%. Continue backwash for a period of 5
minutes, or longer until the water runs clear, or turbidity has dropped below the set point.
5. Place the filter into run phase mode with the water going to waste, wind up pump velocity over a
period of 30 seconds to the required velocity. This is referred to as the rinse phase, continue to
discharge water to waste for a period of 5 minutes, this allows the bed to compact.
6. Check that there is no air or vent the air on top of the filter.
7. Place the filter on-line.
5.9.
RGF Rapid Gravity Filter backwash procedure
The following sections relate to the operational protocols for RGF rapid gravity filters for drinking water.
The backwash procedure will vary depending upon the manufacturer’s instructions. The following is a
generic backwash procedure.
Backwash steps, rapid gravity filter:
Dryden Aqua Ltd
Butlerfield-Bonnyrigg,
Edinburgh EH19 3JQ Scotland
Page 26 of 44
1. Turn off pumps or stop water flow through the
filter.
2. Place filter into backwash mode.
3. Air purge is not required for AFM®, but if it is
used, air flow velocity is 55m/hr for 3 minutes. If
air purge is applied, drop water level 100mm
below the cill before turning on the air blowers.
We do not recommend running the air blower
and backwash at the same time, this strategy
results in loss of too much of the filter media.
4. Turn off air supply and start up backwash pump.
The objective is to achieve a 20% bed expansion for a period of at least 3 minutes. Gradually
increase backwash flow rate over a period of 30 seconds to the full flow rate. See Table 3 for flow
rates. Flows are in accordance with European Standards. For filters in accordance with UK
procedures when air scour is used the water flow rate for backwash may be reduced.
5. Continue the backwash for a period of at least 3 minutes at full backwash flow-rate, or until the
water runs clear.
6. Clean, filtered water should be used to backwash the filter.
7. After backwash place the filter onto rinse cycle and run for a period of 5 minutes to waste before
going back on-line with the system.