Cleaning methods for combined air filters

The cleaning methods for combined air filters should be differentiated and handled based on the type of filter material, filtration level, and degree of pollution. Improper cleaning may lead to filter material failure or secondary pollution. The following are detailed cleaning guidelines and precautions for different components:
I. Cleaning Specifications for Primary Filters
1. Washable types and applicable scenarios
Common types: Plate-type primary filter (G3-G4, filter material is non-woven fabric, metal mesh, or nylon mesh), pleated primary filter (filter material is polyester fiber).
Applicable scenarios: It is suitable for scenarios with large dust particles and low pollution levels (such as the initial filtration of air conditioning fresh air systems), and it is necessary to confirm that the product instructions allow cleaning (some disposable primary filters cannot be cleaned).
2. Cleaning steps and methods
Disassembly and pre-dust removal
Turn off the power of the fan and remove the filter in the opposite direction of the airflow to prevent dust from scattering.
Blow compressed air (with a pressure of ≤0.4MPa) from the air outlet side to the air intake side to remove large particles of dust on the surface (or gently brush with a soft-bristled brush to avoid damaging the structure of the filter material).
Chemical cleaning
Neutral detergent cleaning: Soak the filter in a neutral detergent solution (concentration 1-2%) at a temperature below 50℃ for 10-15 minutes, and then wipe the stains with a soft sponge (do not use steel wool balls or hard brushes).
The primary effect of the metal mesh can be cleaned with a weakly alkaline detergent (pH≤9). When removing oil stains, a small amount of surfactant (such as dishwashing liquid) can be added.
Rinsing and drying
Rinse the filter material with clean water until no foam remains. The water flow direction should be consistent with the normal air flow direction (to avoid entanglement of the filter material fibers).
Place it in a well-ventilated area to air dry naturally (temperature ≤40℃), or dry it with hot air below 60℃. Do not expose it to direct sunlight or high-temperature baking (to prevent deformation of the filter material).
3. Cleaning limitations and replacement indications
Cleaning frequency: For the primary effect of non-woven fabric, it should be no more than 5 times; for the primary effect of metal mesh, it should be no more than 10 times. If the frequency exceeds the limit, the filter material fibers will wear out or the pore size will increase, and the filtration efficiency will drop by more than 20%; it must be replaced.
Damage repair: If the filter material has holes (diameter > 5mm) or the frame is deformed, it cannot be used any longer and needs to be replaced as a whole.
Ii. Precautions for Cleaning Medium Efficiency Filters
1. Washable types and limitations
Only some types allow cleaning:
Among the medium-efficiency bag-type filters (F5-F8, with synthetic fibers or glass fibers as filter materials), some manufacturers' "washable" bag-type filters (such as polyester fiber filter bags with support frames) can be cleaned, but the instructions should be referred to.
Most of the plate-type medium-efficiency filters (F7-F9) are for single use only and are not allowed to be cleaned (the filter material has a high density, and it is difficult to restore the filtration efficiency after cleaning).
2. Cleaning Process (Taking a washable bag-type medium efficiency as an example)
Low-intensity cleaning
Rinse the bag from the inside out with low-pressure water flow (≤0.2MPa) to prevent the filter bag from expanding and bursting.
Use neutral detergent (pH=7-8), and soak for no more than 5 minutes. Do not rub or wring out (deformation of the filter bag may cause air leakage).
Drying requirements: Lay the filter bags flat to air dry, avoiding folding or heavy pressure. After drying, check if the filter bags have returned to a fluffy state. If they become hard or have fiber lumps, replace them immediately.
3. Situations where cleaning is prohibited
The filter material is glass fiber or electrostatically charged material (such as F9 grade medium efficiency). Cleaning it will damage the fiber structure or electrostatic layer, causing a sudden drop in filtration efficiency.
When the resistance of the medium-efficiency filter exceeds 50% of the final resistance (for example, the final resistance is 250Pa, and the current resistance is ≥125Pa), cleaning cannot effectively restore the filtration performance, and it needs to be replaced directly.
Iii. Principles for Handling High-Efficiency and Special Function Filters
1. High-efficiency filters (HEPA/ULPA
Prohibited from cleaning:
The filter material is made of superfine glass fiber or polypropylene fiber, presenting a folded and closely pleated structure. Cleaning may cause:
The filter material fibers break, creating gaps of ≥0.3μm, and the filtration efficiency drops from ≥99.97% to < 90%.
The sealing rubber strip expanded and failed when exposed to water, causing air leakage from the filter frame.
The correct handling method: Replace the entire device when the final resistance or service life is reached. Waste filters should be treated as general solid waste (for non-medical scenarios) or special waste (for medical/biological scenarios).
2. Activated carbon filter (Deodorization/Chemical Filtration section)
Non-washable regeneration: Once activated carbon reaches adsorption saturation, cleaning cannot restore the pore adsorption capacity, and moisture will cause the activated carbon to clump, increasing resistance.
Replacement cycle: Depending on the concentration of pollutants, it is usually replaced every 3 to 6 months. If it is used for formaldehyde purification, it can be determined by weighing (replacement is required when the weight increases by 15% to 20%).
3. Antibacterial/anti-mold filter
Cleaning surface antibacterial coatings (such as nano-TiO₂ or silver ion coatings) can damage the coating structure and lose their antibacterial effect. It is recommended to use ultraviolet irradiation (wavelength 254nm, irradiation time ≥30 minutes) or ozone disinfection (concentration ≤0.3ppm, action time 1 hour) instead of water washing.
Iv. Key Points for Performance Verification and Maintenance after Cleaning
1. Cleaning effect detection
Visual inspection: After cleaning and drying, the surface of the filter material should be free of obvious stains, damage, or fiber shedding, and the metal frame should be free from rust.
Resistance test: The initial resistance of the filter after cleaning should not exceed 110% of the original initial resistance (for example, if the original initial resistance is 50Pa, it should be ≤55Pa after cleaning). Otherwise, it indicates that the filter material is clogged or structurally deformed.
2. Cleaning frequency and record management
It is recommended that the primary filter be cleaned every 1 to 2 months (depending on the air quality; on hazy days, it can be shortened to 2 weeks), and the medium filter be cleaned every 3 to 6 months.
Establish a cleaning ledger, recording the time, method, resistance data, and frequency of each cleaning. Replace promptly when the replacement threshold is reached.
3. Alternative solutions for special scenarios
In high-humidity environments, such as basement air conditioning systems, washable metal mesh filters (such as G4 grade aluminum mesh filters) can be selected as the primary filters to reduce mold on the filter materials caused by moisture.
Fume environment: The primary efficiency section of the kitchen exhaust unit can adopt an "automatic winding filter" (the filter material can be automatically replaced), avoiding the trouble of manual cleaning of grease.
V. Cleaning Safety and Protection
Personal protection: When cleaning filters in medical/industrial Settings, wear a dust mask (N95 grade) and rubber gloves to prevent dust or contaminants from coming into contact with the skin.
Wastewater treatment: When cleaning filters containing oil stains or chemical pollutants, the wastewater must be separated from the oil stains or neutralized before being discharged, meeting environmental protection standards (such as COD≤500mg/L).
Summary
The cleaning of combined air filters must strictly follow the principle of "graded treatment and type matching": primary filters can be cleaned to a limited extent (controlling the frequency and method), medium-efficiency filters only allow low-intensity cleaning for some types, and high-efficiency and functional filters are prohibited from cleaning. The core of cleaning is to restore the filtration performance without damaging the structure of the filter material. At the same time, it is necessary to ensure the filtration efficiency through resistance monitoring and cycle management to avoid an increase in system energy consumption or a decline in air quality due to improper cleaning.