The primary filter is the basic filtering equipment in air filtration systems, mainly used to intercept large particulate pollutants (such as dust, hair, debris, etc.) in the air. It is the "first line of defense" in central air conditioning, ventilation systems, industrial pretreatment and other scenarios. The following provides a detailed analysis from the aspects of definition, classification, application scenarios, performance characteristics, and maintenance points:

1、 Core Definition and Filtering Principle

-Definition:

The primary filter belongs to the primary filtration level of air filters, with a filtration accuracy of usually 5-100 μ m (based on particle size with a filtration efficiency of ≥ 80%), and can filter visible large particulate pollutants.   

-Filtering principle:

Purification is achieved through physical interception (such as fiber pores of filter materials blocking particles) and inertial collision (particles in the airflow are captured by inertial impact on the filter material), without the need for complex chemical or electronic mechanisms.

2、 Classification and Typical Structure

Initial filters can be classified into various types based on their structure and material, suitable for different scene requirements:

Classified by filter material material

-Non woven fabric: affordable and suitable for general environments such as offices and shopping malls.   

-Fiberglass: High temperature resistant (up to 250 ℃), used in industrial high-temperature ventilation systems.   

-Polyurethane sponge: washable and reusable, suitable for high humidity environments (such as bathroom ventilation).   

-Metal wire mesh: high strength and impact resistance, used in high dust or mechanical debris scenarios (such as metal processing workshops).

3、 Application scenarios and selection criteria

1. Core application scenarios

-Central air conditioning and ventilation system:

Installed at the air inlet of the air conditioning unit, it filters dust and pollen in the air, protects the subsequent high-efficiency filter, and extends its service life.   

-Industrial pretreatment:

-Primary filtration in clean workshops such as electronics and food factories reduces the load of subsequent precision filtration.   

-Spray lines, welding workshops, etc. filter oil mist and metal particles in the air to improve the working environment.   

-Commercial and civilian scenarios:

-The fresh air system in office buildings and hotels improves indoor air quality.   

-Pre filter layer of household air purifier (equipped on some models).   

-Special environment:

-Primary filtration in laboratories and hospitals to prevent large particulate pollutants from entering clean areas.   

-Reduce equipment wear and tear in places with high dust such as warehousing, logistics, and garages.   

2. Key parameters for selection

-Filtration efficiency:

According to international standards such as ISO 16890, the efficiency level of primary filters is usually G1-G4 (G1 lower, G4 higher), corresponding to filtration efficiencies (for particles ≥ 5 μ m) of:

- G1：20%-50%  

- G2：50%-70%  

- G3：70%-85%  

- G4：85%-95%  

-Airflow: It is necessary to match the airflow of the ventilation system (such as 1000-10000m ³/h) to avoid a decrease in filtration efficiency due to high wind speed.   

-Resistance and dust holding capacity:

-Initial resistance: generally<50Pa, excessive resistance will increase energy consumption.   

-Dust holding capacity: refers to the larger amount of dust accumulated when the filter reaches its final resistance (such as 100-150Pa). The higher the dust holding capacity, the longer the replacement cycle.   

4、 Performance characteristics and advantages/disadvantages

advantage

-Low cost: The price is only 1/5-1/3 of that of medium/high-efficiency filters, suitable for large-scale applications.   

-Easy maintenance: Most of them are designed for one-time use and easy to replace; Some washable filter materials (such as sponges) can be reused.   

-Strong compatibility: can adapt to various ventilation systems, with low requirements for installation space.   

disadvantage

-Limited filtration accuracy: unable to remove tiny particles such as PM2.5 and bacteria, it needs to be used in conjunction with medium efficiency and high-efficiency filters.   

-Short service life: In high dust environments (such as near construction sites), it may be necessary to replace it once a month.   

5、 Key points for maintenance and replacement

1. Determination of replacement cycle:

-Observation method: When the surface of the filter material is significantly blackened and the dust accumulation thickness is greater than 2mm, it needs to be replaced.   

-Differential pressure method: By monitoring with a differential pressure gauge, when the resistance reaches twice the initial resistance (such as increasing from 50Pa to 100Pa), replace it in a timely manner.   

2. Cleaning precautions:

-Only filters labeled as "reusable" (such as polyurethane sponge) can be cleaned. Gently rinse with neutral detergent, air dry, and then install.   

-Disposable filter materials such as non-woven fabrics and fiberglass should not be cleaned to avoid damaging the fiber structure and reducing filtration efficiency.   

3. Environmental protection treatment:

If the discarded primary filter is made of ordinary materials (such as non-woven fabric), it can be treated as dry waste; If exposed to harmful pollutants (such as chemical dust), they must be treated according to hazardous waste standards.   

6、 Collaborative application with medium/high efficiency filters

The primary filter is usually used as the "first stage" of a three-stage filtration system, in conjunction with medium efficiency and high-efficiency filters

-Initial effect (G grade): Filter large particles (≥ 5 μ m) to protect subsequent filter materials.   

-Medium efficiency (F-grade, filtration accuracy 1-5 μ m): Filter medium particles to further purify the air.   

-Efficient (H-level, filtration accuracy ≥ 0.3 μ m): Filters small particles (such as bacteria, viruses, PM2.5), used in high-precision scenarios such as cleanrooms.   

Example: Air filtration process in electronic chip workshop:

Outdoor air → Primary filter (G4) → Air conditioning unit → Medium efficiency filter (F8) → Fan → High efficiency filter (H13) → Workshop air supply

Summary: The core value of primary filters

The primary filter is the "pre barrier" of air filtration. Although the filtration accuracy is not high, it significantly prolongs the service life of medium and high efficiency filters by intercepting large particulate pollutants, and reduces the overall operating cost of the filtration system. When selecting, it is necessary to choose the appropriate structural form and efficiency level based on the specific dust concentration, air volume requirements, and budget of the scene, and regularly maintain and replace them to ensure the efficient operation of the ventilation system.