AFM ® operating criteria:
Recommended filtration speed:
15 - 30 m/hr
AFM operates over a wide range of water flows but
like any filtration media, performance improves as
you reduce the flow rate. For swimming pool water
filtration the flow should be between 15 - 30 m/hr
however we recommend flows less than 22 m/hr for
best results. AFM ® is a mechanical filtration media
and will remove particles down to 5 microns at a
water flow of 20 m/h. However in addition to acting
as a mechanical filter media, AFM ® also adsorbs
micron and sub-micron particles as well as heavy
metals and dissolved organics, even at slow flow
rates. At high flow rates such as 50 m/hr AFM ®
will also perform much better than sand because
sand filters become bio filters after 6 months which
reduces the filtration performance.
®
Strong negative surface
charge
Recommended layering of AFM ® ?
Quartz sand has a bulk bed density of 1‘450 kg/m 3
– AFM® has a bulk bed density of 1‘250 kg/m 3 . This
means that you require 15 % less AFM ® by weight in
comparison to sand. For example if your filter takes
150 kg of sand, it requires only 125 kg AFM ® .
AFM ® is supplied in 3 different grain sizes and
should be used in swimming pool filters as follows:
AFM ® grain 1
= 0.40 to 1.0 mm in the
upper filter bed (70 %)
AFM ® grain 2
= 1.0 to 2.0 mm support
on top of grade 3 (15 %)
AFM ® grain 3
= 2.0 to 4.0 mm particle size,
on the base of the filter (15 %)
Slip zone (stern layer)
Grain 1 = 70 %
Grain 2 = 15 %
Grain 3 = 15 %
Thin water layer
Negative Zeta potential
Dipolar organics
Backwashing:
What goes into a filter must come back out during
the backwashing stage, because any organic mat-
ter remaining in the filter acts as a food source and
substrate to support the growth of bacteria. All sand
filters and crushed glass filters will support a biofilm.
The biofilm is an alginate jelly 50 microns thick which
protects the bacteria from chlorine leaving them free
to multiply. The alginate forms a sticky layer which
makes it difficult to remove all of the fine solids that
have been filtered from the water. For this reason,
sand requires high water flow rates of 60 m/hr (From
German DIN standard) for an effective backwash.
However, bacteria and biofilms will continue to deve-
lop, so even these high flow rates are not effective at
completely cleaning the sand during a back-wash.
When AFM ® is compared against sand and crushed
glass, up to 30 % more solids are removed from an
AFM ® filter operating in the same water under iden-
tical conditions. This means less chlorine is required,
chlorine by-products are reduced and you have a
much safer water and air quality for bathers and pool
staff.
The recommend operational criteria for an AFM ®
filter are as following:
• Air purge: 60 m/hr (optional not essential for AFM ® )
• Backwash /water): 40 - 50 m/hr at a temperature
between 25 and 32 ˚C of freshwater. With a bed
expansion of 15 % of the filter bed you have a
good backwash process
8
DRYDEN AQUA
If the filter is less than 1‘000 mm in diameter then
just grade 1 and 2 may be used (70 % grade 1 and
30 % grade 2). If the filter has a nozzle plate then
irrespective of the filter diameter only 2 grades are
required (85 % grade 1 and 15 % grade 2).
AFM ® is supplied in 21 kg (46 lbs) bags or 1‘000 kg
(2200 lbs) big bags.
AFM ® and sand back flush curve:
70
Positive charged flocs
substances
Back flush profile for sand und AFM ®
60
50
40
Week 1
Week 2
Sand
AFM ®
Sand
AFM ®
30
20
10
30 60 90 120 150 180 210 240 270 300 360 420
Backwash time [s]
The back flush curve compares the backwash of a
sandfilter with an AFM ® filter. With the AFM ® filter,
30 % more particles were washed out .