Bag filter refers to the dust removal equipment that uses fibrous filter bags to capture dust. When the dusty gas passes through the filter bag, the dust is separated on the outer surface of the filter bag, and the clean gas is discharged through the filter bag, so as to achieve the purpose of dust removal. When the dust outside the filter bag accumulates to a certain extent, the wind resistance increases, and it needs to be cleaned. The commonly used cleaning methods include pulse injection, etc. Pulse injection can be divided into two types: "online injection" and "offline injection". 

Online blowing is to place all the filter bags of the bag filter in a box, the filter bags are arranged in several rows, and the dust cleaning is to spray the filter bags row by row. At this time, the remaining rows of filter bags in the bag filter are still in the filtering state, which is called online cleaning. During online ash cleaning, although the filter bag being cleaned has no filtering effect, the filtration effect can almost be regarded as continuous because the injection time is very short and the filter bags are cleaned row by row in sequence. Therefore, it is not necessary to adopt the sub-chamber structure, but for the convenience of maintenance, for large and medium-sized dust collectors, even for online injection, the design of the sub-chamber structure is adopted.

Off-line blowing is to divide the bag filter into several filter bag chambers, and then spray and clean the dust one by one. The off-line cleaning pulse bag filter is usually divided into multiple filter chambers. When cleaning is required, the exhaust valve of the filter chamber is closed, the chamber stops working, and the high-pressure injection gas quickly enters the chamber, causing the filter bag to vibrate. The dust lumps accumulated outside the filter bag shatter and fall, usually after a few minutes, after all the dust has fallen, the exhaust valve opens and the chamber starts to work again.

During online blowing, the filter bag adjacent to the filter bag to be cleaned is still in the filtering state, and the cleaned dust is easily reabsorbed by the adjacent filter bag, resulting in insufficient cleaning. The dust is cleaned by blowing, and the cleaning time is long, so the dust is cleaned thoroughly. At the same time, when cleaning off-line, the pressure of compressed air for blowing is lower than that of on-line blowing under the condition of achieving the same cleaning effect.