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Filter common sense and maintenance management

Views: 1     Author: Site Editor     Publish Time: 2021-12-03      Origin: Site

1. Basic knowledge of the filter

filterIt is the main purification device of the clean room, which is the main means of air purification. Therefore, it is very important for the basic knowledge of clean room design, construction, and maintenance management to understand and master the filter.

a, classification of filters

According to the performance of the filter (efficiency, resistance, dust removal), it is usually divided into a 20-class filter that is coarse, alive, high-efficient, sub-efficient, efficient (HEPA) and ultra efficient (ULPA).


The efficiency and resistance of different filters in my country's national standard \"air filter\" GB / T 14295-93 is as follows:

Filter efficiency and resistance (GB / T 14295-93)


Performance category

Air dust limit counting efficiency under rated air volume


First resistance under rated air volume



≥ 5.0μm

80> e> 20

≤ 50


≥ 1.0μm

70> e> 20

≤ 80


≥ 1.0μm

90> e> 70

≤ 100

Asia high efficiency

≥ 0.5μm

99.9> E> 95

≤ 150

The National Standard \"High-efficiency Air Filter\" GB 13554-92 provides that the high-efficiency filter is divided into four categories of A, B, C, D in performance. Class D is also known as a super high efficiency filter (or a 0.1 μm high efficiency filter or ultra-low transmittance filter).

Filter efficiency and resistance (GB 13554-92)


Performance category



First resistance (PA) under rated air volume


Sodium flame efficiency under rated air volume

≥ 99.9

≤ 190


Rated air volume and sodium flame efficiency under 20% rated air volume

≥ 99.99

≤ 220


Rated air volume and sodium flame efficiency under 20% rated air volume

≥ 99.999

≤ 250


Rated wind content and ≥0.1 μm particle efficiency under 20% rated air volume

≥ 99.999

≤ 280

The filtering efficiency indicator of ultra-efficient filter (ULPA) is specified in the filtering efficiency of ≥ 0.12 μm particles E≥99.9995%.

About my country and European and AmericanfilterThe classification comparison is as follows:

Filter classification table

my country standard

GB / T 14295

General ventilation

Clean room




Asia high efficiency

High efficiency

Super efficient


ASHRAE standard





















European new standard


















European old standard















Efficiency E (%)

65 80 90

60 80 90

85 95 99.5 99.95 99.995 99.9995 99.99995



MPPS method (DOP method)

B, filter of the filter

The filter mechanism mainly has interception (sieving), inertial collision, Brown diffusion, and static electricity.

1 Interception: That is, it is sieved. The particles greater than the sieve holes are intercepted by filtration, smaller than the screen of the screen.

Generally, the large particles have a function, the efficiency is low, and it is a filter mechanism of a coarse filter.

2 inertial collision: The particles are particularly larger particles flow with the gas stream, and there is no regular movement. Due to the inertia of the particles or a certain field force deviates from the airflow direction, it is not filtered from the obstacle, and is bonded to the obstacle, and stick it. The larger the particles, the greater the inertia, the higher the efficiency. Generally, the filter mechanism of a coarse effect and a neutral filter.

3 Brown diffusion: Tiny particles in the airflow do not have a regular Brown movement, and the hit is hooked with the obstacle, and is filtered out. The smaller the particles, the stronger the brown movement, the more the obstacle hits, the higher the efficiency. This is also called diffusion mechanism. This is the filter mechanism of sub-efficient, efficient and ultra-efficient filters. And the closer the diameter of the fiber, the better the particle diameter.

C, the performance of the filter

Filter performance generally includes filtration efficiency E; initial resistance Hc; dust collector g.

1 Filtering efficiency E = total particle amount of particle / unfiltered in front of filter filtered down × 100%

In general, ≤0.1 μm particles are mainly Brown diffusion movement, the smaller the particle size, the higher the efficiency.

> 0.5 μm particles are mainly inertial collision motion, the greater the particle size, the higher the efficiency.

Particles between 0.1> D> 0.5 μm had a minimum point in which the filtering efficiency has a minimum penetrating rate.

2 initial resistance HC: gas stream winding fiber motion produces small resistance, countless minor resistance and the resistance of filter materials to air. The resistance of the filter is related to the airflow speed, the greater the speed, the greater the resistance.

The resistance of the filter is divided into primary resistance (HC) and final resistance (Hz).

The primary resistance (HC) is the resistance of the filter when the filter is started.

The final resistance (Hz) is the resistance of the filter replacement. General Hz = 2 × HC.

3 Cavity G: The filter is received on the filter material when the filter reaches the final resistance.

d, filter speed

The filter speed refers to the speed of the air passing through the filter material perpendicular to the direction of the filter. It is not a filter that is windy.

The larger the filter speed, the larger the particle inertia, the higher the efficiency of the thickness, and the medium-effect filter, the larger the filter speed, the greater the resistance of the filter to the air. Therefore, a generally coarse-efficient filter speed is 1 to 2 m / s, and the filter speed of the neutral filter is 0.2 to 1 m / s.

The larger the filter speed, the brown movement of the small particles, so the filter speed of the high efficiency and super efficient filter is generally controlled at about 0.02 m / s.

e, filter filter and structural form

The filter material of the coarse filter is generally: glass fiber, chemical fiber, non-woven fabric, and other structural types, folded and bag type.

Filtering of the mid-range filter is generally glass fiber, chemical fiber, non-woven fabric, and other structural types, and a wedge fold type.

The filter material of the high efficiency filter is mainly ultra-fine glass fiber filter paper. The structural type is folded. There is a separator and a separator.

f, the use and replacement of the filter

1 Filter use

Coner, high-altitude, high-altitude, sub-efficient, efficient, super efficient 6 filters have their own uses, must be used correctly, if used is improper, not only does not work, but also produce poor or even opposite effects. Therefore, those who design, construction, and maintenance management clean room should pay special attention.

The coarse filter is used as a pre-filter. It is generally arranged in the air conditioner, which function is filtered to filter the particles of large particles to protect the subsequent air-conditioning equipment (such as a semoller and heater, etc.) and Advanced filter. Generally, a coarse-efficient filter cannot be used as a terminal filter.

The mid-range filter is typically provided in the positive pressure segment of the air conditioner, which is to protect the terminal filters such as high efficiency, high efficiency filters. It removes medium and small particles of ≥1.0 μm. In general, the alternating filter is an intermediate filter and cannot be used for pre-filters, and does not do a terminal filter.

Efficient and super efficient filters are used as a terminal filter for purifying systems. Generally placed on the ceiling of the clean room. The high efficiency filter (HEPA) is a must-have end filter for a clean room. The ultra-efficient filter is a terminal filter that must be 0.1μm, 10, 1 or higher level clean room.

2 replacement of the filter

After a period of operation, when the filter is resistant to the final resistance Hz, it will be replaced in general, otherwise its performance will decline, and it will not achieve the role of the response, and even affect the normal operation of the system. .

For coarse, mid-range filters, there is also a disposable use, there is also a cleaning, but the coarse, the resistance of the coarse filter after cleaning is much larger than its initial resistance, and the efficiency has improved.

However, As high efficiency, efficient and super efficientfilterThey are all one-time, and the final resistance needs to be replaced in time after use.

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