5.2 After-filter: If an after-filter has been installed in the system to
collect an initial plume of dust that might be blown from the gas phase
chemical filters, it can eventually be removed from the system to reduce
the energy required to operate the system. Monitor the pressure drop
across this filter, and when the pressure ceases to increase it is safe to
remove this filter from the system. This should typically be no longer
than after 40 hours of operation. If after-filters still have significant life
remaining at the time of removal (based on the pressure drop reading)
they should be retained for re-use as after-filters following the change-out
of the chemical filters or be used as replacements for the prefilters.
5.3 Gas Phase Filter Monitoring: A discussion of sophisticated gas
phase filter monitoring is beyond the scope of this manual. At its most
simple, when the filter is used to remove nuisance odors, the time to
change out the gas phase chemical media cassette is when the odor
begins to be regularly detected on the clean side of the filter bank. In
more stringent applications where the system is supplied to protect
health and / or high value plant and product, active real time
electronic and passive coupon corrosion monitoring systems are
available to determine the performance of the system. The remaining
life of the media in the SAAF Cassette can be determined by taking a
sample of media and returning it to AAF for analysis. Consult with
your AAF representative regarding active and passive monitoring
systems and media sampling for remaining life analysis.
5.4 Removal and Replacement of Particulate and Gas Phase
Chemical Filters: Removal of filters will be the reverse of the
installation process described earlier in this manual. Filter replacement
will be carried out exactly the same as at initial installation.
5.5 Disposal of Used Filters: Used chemical filters and particulate
filters shall be packaged and disposed of in full accordance with all
required and applicable laws and regulations. Consult with local
environmental control authorities such as local, state, and federal EPA
& OSHA authorities for direction. Material Safety Data Sheets (MSDS)
are available on all products supplied by AAF. Contact your AAF
representative for further information.
5.6 Gaskets: The proper maintenance of the face gaskets on the
leaving air face of each FAH is critical to the performance of the
system. Check the gaskets carefully whenever the gas phase
chemical filters are replaced. If gaskets are worn, frayed, or
compressed to the point where they do not recover when the filter
seal is released they should be replaced. Check the seal between the
gas phase chemical filter cassette and the FAH on the air leaving face
of the housings whenever new SAAF Cassettes are installed.
5.7 General System Maintenance: Ducts, filter support frames,
access doors, and other system infrastructure should be checked at
least every 6 months. Examine all components for the following:
5.7.1 Cleanliness: Sweep and vacuum all standing dust or dirt in the
system and damp wipe all surfaces. Be mindful of the impact of
cleaning solvents on the performance and life of the gas phase
chemical filters and take appropriate precautions to protect the system.
5.7.2 Water: The system should be completely dry at all times. The
presence of standing water, condensation, or dampness is
detrimental to the performance and life of the system. Determine
and remove the cause for the presence of water in the system, dry
the system, and examine all components for the presence of mold
and other biological growth. Remove all contamination, clean and
sterilize as necessary.
5.7.3 Filter Bank Integrity: Ensure that all filter housings contain
the appropriate filter elements, both particulate and gas phase, and
that these elements are correctly installed. Check for missing or
improperly installed latches and review the filter seals. Check for air
leaks between the housings and seal with caulk as necessary.
5.7.4 Duct and System Integrity: Examine the entire system to
ensure that contaminated air cannot leak around the filter bank.
Check all perimeter seals and repair as necessary.
5.7.5 Corrosion: If metal components are corroded, repair the
corrosion and provide protective coatings as necessary. Be mindful
of the impact of painting on the performance and life of the gas
phase chemical filters and take appropriate precautions to protect
the system. Determine the source of the corrosion and rectify.
6.0 Troubleshooting
6.1 High Pressure Drop Reading Across the Filter System:
6.1.1 High Dust Loading: The most probable cause of high
pressure drop will be high dust loading of the particulate filters. The
rate of dust loading may not always be constant and may be
significantly affected by season and location; e.g., the timing of pollen
blooms, production schedules, and rural versus urban locations.
6.1.2 High Airflow Volume: High airflow volume may result from
improper fan sizing or improper control of the fan. When clean
particulate filters are installed in the system the pressure drop
across the system will decrease and the airflow will normally
increase. The airflow should be controlled through the use of
modulating dampers which are designed to keep the system
pressure constant or with the use of variable speed drives. If
desired, the filter system may also be slightly oversized so that it
will handle the higher airflow at the lowest system pressure without
exceeding the recommended filter face velocity.
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