Pocket filter and primary filter are adopted aluminum frame and synthetic filter media. It will not be deformed, cracked, twisted under normal operating conditions. In addition, the filter box is diagonally fixed before and after the frame. Filter and the frame close adhesion frame to prevent any air leakage. This series of products folding filter can be larger dust accumulated in the bottom of the fold, both sides can effectively filter other dust. In general, the deeper the fold, the longer the service life. This series of products have the following characteristics: Solid structure Filtering effect is stable, extending service life Rugged, efficient and easy to handle Low initial resistance Filtration efficiency and stability Primary filter include panel primary filter, pleated type filter, washable filter and other primary filter.