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Purpose and methods of ventilation duct cleaning in clean workshops
2026/8/27
The following is a detailed analysis of the purpose and specific operation methods of ventilation duct purging:
01 The purpose of ventilation duct purging
Remove construction residues: Remove welding slag, floating dust, oil stains, and other construction debris left in the duct during fabrication and installation to prevent these impurities from entering the clean area and causing contamination.
Ensure process and product purity: Avoid particles or impurities in the duct contaminating the production environment and preventing cross-contamination, thereby ensuring the quality of the final product (such as avoiding the activation of catalyst due to trace metal impurities, etc.).
Protect equipment from wear: Remove particles to prevent them from wearing out the precision components such as fan blades and valve sealing surfaces during system operation, ensuring the stable operation of the equipment.
Meet compliance and acceptance requirements: Ensure that the air cleanliness, wind speed, etc. of the cleanroom meet the relevant national standards and design requirements, laying the foundation for the installation of high-efficiency filters and system commissioning.
02 Methods of ventilation duct purging
The purging of ventilation ducts in the cleanroom is mainly divided into empty blowing during the construction stage and graded purging before completion. The specific methods and operation points are as follows:
1. Empty blowing during the construction stage (system empty blowing)
After the new air filter and pre-filter are installed and the air conditioning equipment and ducts are thoroughly cleaned, it is carried out.
Circulating empty blowing: It is advisable to close the new air inlet and use circulating air. Set a pre-filter device equivalent to a medium-efficiency filter at the return air inlet for full air blowing (usually requiring empty blowing for more than 12 hours).
Subsequent treatment: After the empty blowing is completed, the cleanroom needs to be cleaned and wiped again, and then the sub-high efficiency or high-efficiency supply end devices should be installed immediately.
2. Graded and segmented purging before completion, carried out after all ducts are installed and before connecting the high-efficiency filter.
Graded air volume control: First, start with low air volume for pre-blowing, then gradually increase to the rated air volume, and carry out regional circulating dust removal, focusing on cleaning the residual floating dust in the ceiling and the corners of equipment.
High-pressure air/nitrogen purging: Use high-pressure air or high-purity nitrogen (dew point ≤ -40℃) to perform powerful purging on the inside of the duct. The airflow velocity should be greater than 20m/s to ensure that impurities are effectively removed.
Physical mechanical cleaning: For areas with heavy dust accumulation, use robot cleaning, high-pressure water guns or dedicated cleaning equipment (such as rotating brush heads) combined with vacuum suction devices for cleaning. During the cleaning process, keep the duct internal negative pressure.
03 Inspection and qualification standards after purging
After the purging operation is completed, strict inspection must be carried out to ensure compliance:
Target plate inspection method: Set a wooden/aluminum target plate with a white cloth or painted with white paint at the exhaust port. After continuous purging for 5 minutes, if there are no rust, dust, moisture, or other visible debris on the target plate, it is considered qualified.
Dust particle detection: Conduct dust particle concentration detection on the cleaned duct system to ensure it meets the ISO 14644-1 or related cleanliness standards requirements.
Sealing protection: After the purging acceptance is qualified, immediately seal the duct opening with a sealing cover or plastic film to prevent secondary contamination until the high-efficiency filter is connected.
04 Safety and precautions
Isolation protection: Before purging, the equipment that is not allowed to be purged (such as precision instruments, regulating valves, safety valves, etc.) must be isolated from the purging system or protected by passing through a bypass, etc.
Purging sequence: Purge in the order of "main pipe → branch pipe → drainage pipe" to avoid the backflow of dirty substances into the already qualified ducts.
Safety protection: The discharge outlet of high-pressure purging should be led to a safe area outdoors, the exhaust pipe should be inclined upward and set a restricted area, and no irrelevant personnel should approach to prevent injury from rebound force or debris.
