Most of ventilation system problems can be avoided by periodic maintenance and checked by taking measurements of air speed or pressure in the system. Airflow at the hood can be visually checked with inexpensive smoke generators (smoke tubes) or measured with air velometers. Ventilation specialists may be needed to fix or redesign more complicated ventilation problems.
The following simple checklist can be used to evaluate the functioning of ventilation system without extensive measurements or expert help.
| Observation | Yes | No |
Is the fan belt broken or slipping? | | |
Is the fan wired backwards (reversed polarity)? | | |
Is duct clogged with dust? | | |
Is there holes, cracks or openings in the ducts? | | |
Is the air cleaner clogged? | | |
Are any dampers in the duct closed? | | |
Is there insufficient makeup air? | | |
Have ducts been changed to include more length, more or sharper bends, or abrupt diameter changes? | | |
Have additional hoods and ducts been added? (Without proper airflow balancing, some hoods in a multiple system may have inadequate flow or the fan may be too small to handle the additional resistance.) | | |
Has the contaminant source been moved further away from the hood opening? | | |
Is the canopy hood located as close to the source as possible without letting the employees work over the source? | | |
Is an access to enclosing hoods provided? | | |
Is more contaminant being generated at the source? | | |
Are cooling fans causing cross drafts? | | |
Have employees modified the hood because it interferes with their job tasks? | | |
|
| Problems | Possible Cause(s) |
| Frequent clogging | - Improper filter type and/or installation.
- Improper bag cleaning cycles.
- Water intrusion into the filter.
- Filter hopper not continuously emptied and cleaned.
- Improper "clean start-up procedure" for new bags.
|
Visible dust in baghouse
on the clean air side or
in exhaust stack | - Bags installed improperly.
- Torn or damaged bags.
- Leakage between bags and housing.
- General filter fabric failure.
|
Sudden increase in
pressure drop | - Excessive dust loading due to lack of maintenance and scheduled cleaning.
|
| Dirty re-circulated air | - Dirty filters.
- Air bypassing filter section (rip or tears in filter).
- Dirty air handling cabinet housing.
- Exhaust stacks placed close to supply air intakes.
|
| Visible mould or slime | - Drain pans not operating properly.
- Drain pans overflowing.
|
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