Generally new filter efficiency is not high enough. Filter used for a period of time, due to screening such as stranding, collision, and diffusion, electrostatic effects, a layer of dust accumulation on the surface of the filter bag, this layer of dust called the first layer, after this process, layer filter main filter at the beginning, relying on the role of early, large mesh filter can also obtain high filtration efficiency. With the accumulation of dust on the filter surface, corresponding increases efficiency and resistance of the filter when filter pressure difference on both sides of a large, attached some squeezed past tiny dust particles on a filter, filter efficiency decreases. In addition, higher dust resistance will cause significant drop of air cleaning system. Therefore, the filter resistance to reach a certain value, cleaning in time. Cannot be damaged when cleaning to avoid inefficiency.