The medium efficiency filter is mainly used to filter 1~5 μm dust particles, as intermediate filtration of central air conditioning and centralized air supply system, to protect the after end filters and the system itself, in places where the air cleanliness requirements are not strict, the air treated by the medium filter can be directly sent to the user. Medium efficiency filters are divided into two types: pocket type and non-pocket type, of which pocket type includes G4, M5, M6, F7, F8, F9, and non-pocket type includes FB (panel medium efficiency filter), FS (separator type medium efficiency filter), FV (combined medium efficiency filter), etc.