The relationship between the initial resistance of a filter and the filtered particles, filtration class, and filtration precision is an interrelated influence. The particle size and proportion of filtered particles determine the trend of initial resistance change. A higher filtration class generally leads to a greater initial resistance, and a finer filtration precision usually also results in a higher initial resistance. These three factors interact to jointly affect the initial airflow resistance characteristics of the filter.
I.Relationship with Filtered Particles
The initial resistance of a filter is directly affected by the particle size and proportion of the filtered particles:
1.Large particles (≥5μm): Such particles are mainly captured by the filter media through inertial collision and interception. They tend to clog the surface pores of the filter media, directly causing an increase in initial resistance. The larger the particles and the higher their proportion, the more obvious the increase in initial resistance. For example, primary filters that filter a large amount of large particles such as dust and hair will have a faster increase in initial resistance due to particle clogging.
2.Small particles (<5μm): Small particles need to be captured by diffusion or electrostatic adsorption of the filter media. They have little effect on the initial resistance in the initial stage. However, the higher the proportion of small particles, the more likely they are to cause deep clogging of the filter media over time, accelerating the growth rate of initial resistance in the later stage.
II.Relationship with Filtration Class
Filtration class represents the efficiency level of a filter. Generally, a higher filtration class leads to a greater initial resistance, and the two are positively correlated:
1.Primary filters (G1-G4): The initial resistance of G1 class is ≤30Pa, G2 class is ≤45Pa, G3 class is ≤60Pa, and G4 class is ≤75Pa. As the class increases by one level, the interception efficiency of particles improves, and the density of the filter media also increases, resulting in an increase in the resistance to airflow.
2.Medium efficiency and above filters: The initial resistance of medium efficiency filters (F5-F6) is 70-90Pa, and that of high efficiency filters (H13) can reach 180-300Pa. As the filtration class increases to medium efficiency and high efficiency, the structure of the filter media becomes denser, the resistance to airflow increases significantly, and the initial resistance also increases substantially.
Relationship with Filtration Precision
Filtration precision refers to the minimum particle size that a filter can retain. Generally, the finer the precision (the smaller the retained particle size), the higher the initial resistance, and the two are also positively correlated:
1.Filters with low filtration precision (such as those retaining particles ≥5μm) have larger pores and loose structures in the filter media. When airflow passes through, the resistance is small, and the initial resistance is generally between 20-50Pa.
2.Filters with high filtration precision (such as high efficiency filters retaining particles ≥0.3μm) have extremely small pores and dense structures in the filter media. When airflow passes through, the friction and resistance increase, and the initial resistance will increase significantly, reaching more than 200Pa. However, some filter media using special processes (such as PTFE-coated filter cartridges) can achieve high-precision filtration while reducing the initial resistance.
