The previous old customer came to ask me recently: Our high-efficiency HEPA filter has been in use for five or six years, and our production leader ask me to replace it. I feel the filters are all good, and the cleanliness can be achieved. Why do we need to replace it? In this post, we will share with you about air filter replacements.

air filter (1)

By the way, you all said that the final resistance of the high-efficiency filter is replaced when the final resistance of the high-efficiency filter reaches 1, 5~2 times the initial resistance. The initial resistance is marked on the label of the filter. How to measure it? Ok, let me answer this question here.

The filtration efficiency of primary, medium, and high-efficiency filters.

The initial resistance of the filter has a great relationship with the airspeed and the thickness of the filter material. Generally speaking, the airspeed is high, the resistance is large, the filter material is thick, and the resistance is small (except the bag type).

The filtration efficiency of the primary filter: G1:40%@5.0μm G2:65%@5.0μm

air filter (2)

G3: 85%@5.0μm G4: 90%@5.0μm

The filtration efficiency of the medium-efficiency filter: F5:45%@1.0μm F6:65%@1.0μm (or M5 M6) F7:85%@1.0μm F8:90%@1.0μm F9:95%@0.5μm

The filter of medium efficiency filter: H10:85-90%@0.3μm H11:95-99%@0.3μm H12: 99.5-99.9%@0.3μm

The filtration efficiency of the high-efficiency filter: H13: 99.97-99.99%@0.3μm H14: 99.995-99.999%@0.3μm

The filtration efficiency of the ultra-high efficiency filter: U15: 99.9995%@0.12μm U16: 99.99995%@0.12μm U17:99.999995%@0.12μm

Suggested values for the initial resistance and final resistance of the primary, medium, and high-efficiency filters

The initial resistance is the initial resistance of the filter in the clean state, and the final resistance is the resistance at the end of the filter life. At the end of the life, the pressure difference or pressure drop value according to the standard or the agreement between the two parties is used to calculate the resistance according to the mathematical model or design. The resistance value calculated by the empirical formula of materials, etc. is generally only used as a reference.

Recommended initial resistance (Pa) for primary, medium, and high-efficiency air filtration:
G3 (initial effect) 30~40Pa
G4 (initial effect) 40~50Pa
F5~F6 (medium efficiency) 70~90Pa

F7~F8 (high and medium efficiency) 70~90Pa
F9~H11 (sub-high efficiency) 110~150Pa
H13 (high efficiency) 180~300Pa
(The average value can be selected)

Recommended final resistance (Pa) for primary, medium, and high-efficiency air filtration:
G3 (initial effect) 100~200Pa
G4 (initial effect) 150~250Pa
F5~F6 (medium efficiency) 250~300Pa
F7~F8 (high and medium efficiency) 300~400Pa
F9~H11 (sub-high efficiency) 400~450Pa
H13 (high efficiency) 400~600Pa
(The average value can be selected)

The resistance of the new filter (under the lowest airspeed) is called the “initial resistance”, and the resistance when the filter is scrapped is called the “final resistance”. In most cases, the final resistance is the initial resistance. The resistance value is generally its average value.

There are many suggested replacement times on the Internet, which I summarize as follows.

1, Differential pressure gauge reading method for air filter.

Just put the two tubes of the differential pressure gauge at one inlet and one outlet of the high-efficiency filter, and read them directly (of course, if there is no place to put them, this method will not work)
2, Airspeed test method.
Use the airspeed tester to measure the airspeed to see if it does not meet the design requirements. For example, the standard specification of a 500 air volume filter is 320*320, and the calculation is 500/3600/0(0.320*0.32)=1.356m/s.
If the airspeed is lower than this…the air volume will not be reached. Of course, sometimes there is a margin in the design, and even 300 air volume can be used.

3. The pressure difference method between the cleanroom.

No matter how it is adjusted, the pressure difference in the purification room does not meet the original requirements. The filter is likely to be replaced.

4. Time method, because the material of the filter has a certain safety life and the inevitable growth of bacteria and aging after installation. The primary filter is generally replaced once after 3 months of use. The medium-efficiency bag filter should be replaced within 6 months of use.
The high-efficiency HEPA filter can be replaced after use for about 1 year. If the primary filter is replaced frequently, the service life of the rear filter can be appropriately extended and the operating cost can be reduced.

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