Millistak+HC AppGd_textC.qxd - Millipore

are shown in Figure 11. When the
dominant capture mechanism is
adsorption, filtrate turbidity will be
seen to rise markedly, as the capacity
of the prefilter is reached, while the
pressure differential across it rises more
slowly; this profile is known as “breakthrough
limited.” When the dominant
capture mechanism is mechanical
sieving, the pressure differential
across the prefilter will be seen
to rise markedly, as its capacity is
reached, while filtrate turbidity rises
Feed
Pump
Figure 12. Test Configuration for
Millistak+ HC Filter
Prefilter
Millistak+ HC Filters Application Guide
P
P
Sterile
Filter
more slowly; this profile is known as
“pressure limited.” Testing is required to
determine which of these applies and,
therefore, whether a prefilter “pressure
limit” or a “breakthrough limit” should
be employed in overall filter train sizing.
It is strongly recommended that,
during testing of a Millistak+ HC filter,
it should be coupled with a sterilizing
grade filter in series (e.g., 0.22 µm
hydrophilic Durapore cartridge), as
shown in Figure 12. While simulating
the typical filtration process, this test
configuration can tell the user whether
the prefilter is performing correctly, or
if a change needs to be made either
to the prefilter type or to the ratio of
prefilter area to sterile filter area.
If creating a serial filtration test,
as illustrated above, is not feasible,
samples of filtrate from a Millistak+ HC
filter can be collected and tested
off-line, as prescribed by Millipore’s
Vmax sizing method.
Flux
Flux is an important process parameter,
especially for depth filtration. Flux is
flow rate normalized for filtration area
and is usually expressed in LMH
(liters per hour, per square meter).
Flux is significant also with regard
to the adsorptive contribution of
the Millistak+ HC filter media. The
faster a particle is flowing through a
17