How often should the filter element of an FFU in a cleanroom workshop be replaced?

I. FFU Filter Replacement Cycles (Two-Stage System)

1. FFU Upper Pre-filter (Primary Filter)

Standard cleanrooms: Clean every 2–3 months; replace every 3–6 months; mandatory replacement if pressure drop reaches twice the initial resistance.

High-dust workshops: Shorten replacement interval to 1–2 months.

Timely replacement of the pre-filter is key to extending the service life of the HEPA filter.

2. FFU Internal HEPA Filter

① Time-based reference (assuming proper pre-filter maintenance):

Standard Class 10,000 cleanrooms: 18–24 months;

Class 1,000 cleanrooms: 12–18 months;

Grade A/B sterile high-cleanliness zones: 10–12 months;

Pharmaceutical GMP workshops: Most pharmaceutical companies mandate replacement every 12–18 months for compliance; PAO leak testing and report retention are required after replacement.

② Mandatory pressure-drop replacement criteria (takes precedence over time-based schedules):

Initial pressure drop for new HEPA filters is typically 120–180 Pa; replacement is mandatory when the pressure drop reaches twice the initial value (240–350 Pa). For explosion-proof lithium battery workshops, replacement is recommended at 280 Pa to prevent motor overheating risks.

Replace immediately if any of the following occur, regardless of the scheduled cycle:

FFU airflow velocity drops significantly or fan noise increases;

Airborne particle counts in the workshop consistently exceed limits;

HEPA filter media is damaged, the sealing gasket detaches, or dust leakage occurs.

II. Industry-Specific Summary

Medical Device GMP Grade D Cleanrooms

Pre-filter: Replace every 3–4 months; HEPA filter: Replace once every 18 months; record pressure drop monthly; perform PAO leak testing every 12 months.

Standard Electronics Factories: Pre-filter every 4–6 months; HEPA filter every 2 years.

High-Dust Workshops: HEPA filter requires replacement every 6–12 months. III. Key Points for Operation and Maintenance

Record FFU differential pressure data monthly; maintain the GMP workshop differential pressure log for at least five years.

HEPA filters cannot be washed with water; if clogged, the entire unit must be replaced.

HEPA filter replacement must be performed by qualified personnel, and the workshop may only resume production after passing the aerosol leak test.