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Run
Phase
At start-up always vent the air from the filter,
if you do not remove the air, water hammer
effect could cause some damage to the equipment or disturb the filter
bed. After start-up with water flowing through the filter,
the differential pressure across the filter bed will be 0.1 to 0.25
bar, however as the bed compacts and solids are removed, the
differential pressure will increase. When the differential pressure
has increased to 0.5 bar, the filter should be placed on to
back-wash. If the differential pressure is allowed to increase
beyond 0.5 bar differential, solids could be forced into the filter
bed making it much more difficult to back-wash
clean.
The pumps used to operate the filter
should have a shut off head which is less than the pressure ratting on the
filter. For example if a filter has a maximum working pressure of 2.5 bar,
the shut off head from the pumps should not exceed 2 bar. In the
event of a problem with the filter or the valves, this will allow the
system to fail safe.
Air
purge
After a pre-determined time, or when the
differential pressure reaches 0.5 bar, the filter will need to be
back-washed. The back-wash performance can be improved and water
conserved if an air purge of the bed is employed. Please note that
only DIN standard specification filters designed for air purge should be
used.
The pumps are turned off, and the filter
valves are positioned to the back-wash mode. The drain valve on the base of
the filter may also need to be opened in order to drop the water level in
the filter to just above the filter bed height.
The air blower is turned on, it is
best to use a blower that has a shut off head less than 0.5 bar, or use a
blower set to avoid any pressure in excess of 0.5 bar. High pressures
during air purge could damage the nozzle distribution plate. The air
purge rate is approximately 90 m/hr for a period of approx 5 minutes.
After air purge the filter is back-washed with water.
Back-wash
Turn off the air blower and position the valves for a
back-wash. The back-wash rate is approx 45 m/hr. The pump or
water flow should take at least 20 seconds to increase to full speed,
do not turn the pump straight onto full flow as this can blow or disturb the
filter bed. The filter bed will lift by approximately 15% when the AFM
is being back-washed, the filter bed can be viewed through the window
of the filter. It is important to visually check the filter during a
back-wash. The filter should be back-washed until the water runs
clear, normally this will be half the time is takes for sand
filtration media. Once the back-wash has been
completed, the back-wash pump is turned off, and the valves are
positioned for the rinse phase. Rinse
Phase The run phase pump is turned on
and the water flow allowed to build up to full flowrate over a period of
approx 20 seconds. in critical applications such as drinking water, swimming
pools or whenever the best water quality is required, it is essential
that the filter bed is rinsed for a period of 1 to 2 minutes.
This allows the bed to settle down and stabilize before the filtered water
is returned to the application. |
