Laminar air flow units, dispensing booths, air showers and dynamic pass boxes all clean the air in stages. Each stage protects the next one, so the expensive final filter lasts longer and performs as rated.
Stage 1 — EU 4 pre-filter
The pre-filter takes out the coarse dust that would otherwise load the finer filters. In our equipment it is rated at 90% down to 10 micron. It is the cheapest filter in the unit and the one changed most often.
Stage 2 — EU 7 intermediate filter
The intermediate filter catches finer particles: 95% down to 3 micron. It extends the life of the HEPA filter behind it and keeps the pressure drop across the unit stable.
Stage 3 — EU 14 HEPA supply filter
The HEPA filter is what makes the work zone clean: 99.999% down to 0.3 micron. Because its performance is critical, the unit has a DOP test port so the filter’s integrity can be checked after installation and at regular intervals.
Checking the filters at site
- Air velocity test just below the HEPA filter confirms the airflow.
- HEPA filter integrity test (DOP / PAO) confirms there are no leaks in the filter or its seal.
- Particle count test confirms the cleanliness of the air delivered.
A differential pressure gauge (0–50 or 0–100) on the unit shows when the filters are loading up, so replacements can be planned instead of discovered.
