Initial equipment filter:
  When installing the initial equipment filter, the new filter unit is pushed directly into the filter box body along the track and locked in place. Then, the PVC bag device is placed on the specially designed flange opening and secured with a safety belt to ensure a seal between the PVC bag and the flange. Finally, the PVC bag is folded and the maintenance door is closed to ensure that the PVC bag and the filter unit are all enclosed within the bag-in-bag-out box.
Filter unit replacement:
  When replacing the filter unit, the staff opens the maintenance door, inserts their hands into the gloves on the PVC bag, releases the locking device of the filter unit, slides the used filter unit into the PVC bag, then secures the bag at the center and cuts off some of the bag to remove the discarded filter unit from the box. Next, the new filter unit is placed in a new PVC bag, the new PVC bag is placed over the flange opening and secured, remove the remaining flange opening, put the new bag's gloves inside, secure it and cut it off, then roll up the new bag and close the maintenance door and press it down to complete the entire replacement process.
Equipment features:
  The bag-in-bag-out filter not only uses a safe and quick replacement technology, but its overall strength and air tightness are also highly commendable. Currently, the production of bag-in-bag-out filters in the international community mainly follows the nuclear industry standards of various countries, such as: ASME N509 (air purification equipment and components for nuclear power plants), ASME N510 (testing of nuclear air handling systems), DIN 25496 (ventilation components for nuclear facilities), etc. The equipment box body is usually fully welded in stainless steel, the air tight isolation valve is connected to the box body with a flange, and the connection area is usually sealed with chloroprene sealing gaskets and chloroprene flange gaskets. In special cases (such as high-risk, high-pathogenicity environments), the equipment can withstand earthquakes. The box body and the air tight isolation valve follow the same sealing standards. Under the condition of the isolation valve being closed, the American standard requires a pressure attenuation leakage test under a stable pressure difference of 2500 Pa, and the German standard requires a leakage rate less than 10 l/(hm2) under a stable pressure difference of 2000 Pa. There are two methods for the sealing between the filter unit and the box body structure. In North America, liquid (gel) sealing is usually used, with a special gel ring around the filter unit. When the filter unit is pushed into the filter box, the box structure sinks into the gel and ensures the sealing between the two; in Europe, an inflatable airbag is set between the filter unit and the box body structure. After the filter unit is installed, the airbag is inflated, and a professional device is used to check its sealingity to ensure full sealing. 
  The number of filter units in the bag-in-bag-out filter determines the combination method. The number of filter units placed horizontally is called W, and the number of filter units placed vertically is called H. If a bag-in-bag-out filter is of the 2H2W type, it indicates that there are 2 sets of filter units in both the horizontal and vertical directions, and there are a total of 4 sets of filter units in the box. At the same time, the number of filter units also determines the air volume of the bag-in-bag-out filter. Taking the most commonly used 24-inch × 24-inch (610mm×610mm) HEPA as an example, its filtration air volume at a 250 Pa resistance is 1700 m3/h. Then, the air volume of the 2H2W type filter is 6800 m3/h. When assembling the filter units, the number of filter units in the horizontal direction is limited. For example, the maximum number of groups (3W) that can be placed in a 610 mm × 610 mm filter unit is three. This ensures that during replacement, the operator can smoothly replace the deepest group of filter units. In the vertical direction, there are usually no specific constraints, and they can be determined based on the actual situation on site.
  The greatest feature of bag-in-bag-out filtration is that all operations, replacements, and inspections of the filter are carried out under the protection of PVC bags (or high-temperature bags). The filter units do not come into contact with the outside air, thus ensuring the safety of personnel and the environment, making the replacement process convenient and fast.

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