Daily maintenance of fan filter units (FFU/BFU)

The daily maintenance of the fan filter unit (FFU/BFU) directly affects its cleaning efficiency, service life, and operational safety. Targeted maintenance plans should be formulated based on the type of equipment and application scenarios. The following elaborates on aspects such as the maintenance cycle, core projects, key points of special scenarios, and fault handling:
I. Maintenance Cycle and Core Projects
Daily/shift inspection (basic check)
Check item operation method, judgment standard, exception handling
During operation, listen for abnormal sounds from the motor and check the indicator light (green is normal). If there is no abnormal noise (≤65dB), but the indicator light remains constantly on and makes abnormal sounds, it may indicate bearing wear and the machine needs to be shut down for maintenance
The differential pressure monitoring reads the differential pressure gauge of the primary/high-efficiency filter (installed on the side of the box). The differential pressure of the primary G4 is ≤250Pa and that of the HEPA is ≤400Pa. If the differential pressure exceeds the upper limit, it indicates that the filter is clogged. It is necessary to record and plan for replacement.
The hot ball anemometer is used for wind speed detection at the center of the air outlet (10cm away from the air outlet). The standard wind speed is 0.3-0.5m/s (fluctuation ≤±10%). If the wind speed is too low, it may be due to filter blockage or a decrease in motor speed
2. Monthly/quarterly deep maintenance (requiring shutdown operation)
Primary filter cleaning/replacement:
Operation: Remove the primary filter bag (G3/G4), and use compressed air (≤0.6MPa) to blow off the surface dust in reverse, or wash it with water and dry it (water-resistant filter material).
Cycle: In severely contaminated scenarios (such as welding workshops), the replacement should be done monthly, while in ordinary clean rooms, it should be done quarterly.
Maintenance of motors and transmission components:
Lubrication: For oil-impregnated bearing motors, apply special lubricating oil (such as lithium-based grease). For maintenance-free motors, check the wear of the shaft sleeve (replacement is required if the gap is greater than 1mm).
Electrical inspection: Use an insulation resistance meter to measure the insulation value of the motor winding (≥2MΩ) to prevent the risk of short circuits.
Box sealing inspection:
Use a smoke tester to inspect the joints (such as filter frames and inspection doors). For smoke leakage areas, apply a sealant (silicone sealant with a temperature resistance of ≥150℃).
3. Annual comprehensive maintenance (executed by a professional team)
Integrity test of high-efficiency filters
Scan the filter frame and filter material with a DOP/PAO aerosol generator and a particle counter. If the leakage rate is greater than 0.01%, replacement is required.
Control system upgrade
The variable frequency FFU updates the control program (such as optimizing the PID regulation parameters of wind speed) and calibrates the differential pressure sensor (with an accuracy of ±5Pa).
Structural strength testing
The roughness of the flameproof surface of the explosion-proof FFU is inspected (Ra≤6.3μm) to ensure compliance with the ATEX certification requirements.
Ii. Maintenance Differences among Different Types of FFU/BFU
Key points for maintaining HEPA/ULPA filters
Special Precautions for a type replacement cycle
In regular HEPA scenarios, the filter material should be replaced every 1-2 years, while in highly polluted scenarios, it should be replaced every 6-8 months. When replacing, dust-proof suits and gloves should be worn to prevent damage to the filter material (creases can cause leakage).
For ULPA semiconductor scenarios, a pre-cleaning program (air-blowing for 30 minutes to expel all remaining particles) must be run before replacement every 6 to 12 months (as nanoparticle clogging is faster), and the entire process should be monitored with a laser particle counter
2. Maintenance of explosion-proof/high-temperature resistant FFU
Explosion-proof type:
Check the sealing ring of the explosion-proof motor junction box every quarter (replace it immediately if it is aged or cracked). It is strictly prohibited to disassemble and assemble it with non-explosion-proof tools.
High-temperature resistant type
After high-temperature operation (such as a 120℃ baking line), it is necessary to wait for the equipment to cool down to room temperature before maintenance to prevent the silicone rubber sealing parts from shrinking due to cold and causing cracks.
3. Medical/biosafety FFU
Wipe the surface of the box and the UV disinfection module with 75% alcohol every week. (The lamp tubes need to be replaced after cumulative use for ≥ 5,000 hours, and the sterilization efficiency will decrease by more than 30%.)
The exhaust air filter of the FFU in the biological laboratory needs to be sterilized under high pressure (121℃ for 30 minutes) by the "Regulations on the Biosafety Management of Pathogenic Microorganism Laboratories" before replacement.
Iii. Core Norms for Maintenance Operations (Pollution Prevention and Safety)
Anti-static measures:
When maintaining the electronic workshop, anti-static clothing should be worn (charge leakage < 0.1 seconds), and anti-static tweezers and screwdrivers (surface resistance 10⁶-10⁹Ω) should be used as tools.
Aseptic operation requirements:
Before replacing the filter of the medical FFU, the operation area should be disinfected with formaldehyde fumigation (10mg/m³) or hydrogen peroxide spray to ensure that the floating bacteria are less than 5CFU/m³.
Safety of High-altitude work
For the maintenance of ceiling-mounted FFU, scaffolding with a load-bearing capacity of ≥200kg/m² needs to be erected, and the workers should wear double-hook safety belts (with a hook spacing of ≥1.5m).
Iv. Typical Faults and Emergency Handling
Fault phenomenon, possible causes, temporary solutions, thorough solutions
When the wind speed drops by more than 50%, the filter is severely clogged or the motor capacitor fails. Temporarily turn on the backup FFU to maintain the pressure in the clean area, replace the filter, and test the motor starting current (normally 1.5-2.5A).
During operation, if the machine suddenly stops, the overload protector trips or there is a phase loss in the power supply, check the three-phase voltage (380V±10%) and reset the protector. Use a clamp meter to measure the three-phase current balance degree (deviation ≤10%).
Abnormal vibration of the box, unbalanced dust accumulation on the impeller, or loose fixing bolts. Temporarily tighten the bolts (torque 15-20N · m), disassemble the impeller, and clean it with ultrasonic waves (if the dust thickness is greater than 2mm, it needs to be replaced)
V. Maintain records and data management
Key Record Sheet:
Filter replacement ledger: Record the replacement date, initial/final value of pressure difference, and cumulative operating time (It is recommended to use an RFID tag for automatic recording).
Performance trend analysis: Draw the wind speed-pressure difference curve every month to predict the filter life (if the pressure difference rises by more than 50Pa every quarter, prompt to stock up in advance).
Intelligent maintenance system
Connect to the building automation system (BMS), set a pressure difference warning threshold (for example, send a text message alarm when the HEPA pressure difference is ≥350Pa), and achieve predictive maintenance (such as calculating the optimal replacement cycle based on historical data).
Vi. Cases of Maintenance and Optimization in Special Scenarios
Semiconductor lithography machine area
Because nano-sized silica dust particles are prone to clogging ULPA, the "pre-filtration + electrostatic dust collection" pretreatment is adopted, which extends the service life of the main filter from 6 months to 10 months.
COVID-19 vaccine production workshop
Nano-silver antibacterial nets (with an antibacterial rate of ≥99%) are installed at the air outlet of the FFU. Combined with weekly ozone disinfection (concentration of 0.5 ppm, action for 30 minutes), it meets the biosafety requirements of a P3 laboratory.
Summary
The maintenance of FFU/BFU should follow the principle of "prevention first and hierarchical implementation": daily inspections focus on monitoring the operational status, regular maintenance centers on consumable replacement and performance calibration, and annual maintenance requires systematic performance verification. For special scenarios such as semiconductors and medical care, it is necessary to formulate specialized maintenance plans in combination with the characteristics of contaminants (such as nanoparticles and pathogens), and at the same time, achieve intelligent management of the maintenance process through digital tools (such as Internet of Things sensors), ultimately reducing operation and maintenance costs while ensuring clean efficiency.