The filter with an embedded transfer window (usually a high-efficiency HEPA or ULPA filter) is the core component for maintaining its clean function. The replacement process must strictly follow the aseptic and dust-free operation norms to avoid contaminating the clean environment inside and around the transfer window. The following are the detailed replacement steps and precautions:
I. Preparations Before Replacement
Confirm the replacement conditions
When the surface of the filter is damaged or deformed, or the resistance detected by the differential pressure gauge exceeds 1.5 times the initial resistance (usually the resistance of a new filter is 200-250Pa, and it needs to be replaced when it exceeds 300-375Pa), or when it reaches the manufacturer’s recommended service life (generally 6-12 months, depending on the cleanliness of the environment), replacement should be arranged.
Prepare new filters of the same model and specification in advance (pay attention to the filtration efficiency grade, such as H13 and H14 grades, which must meet the on-site cleanliness requirements), and check whether the packaging of the new filters is intact and whether there is a certificate of conformity.
Preparation of tools and consumables
Tools: Screwdriver (select cross/flat-head according to the filter fixation method), wrench, lint-free cloth, special tape (such as sealing tape or pressure-sensitive tape).
Cleaning consumables: 75% medical alcohol, sterile water, or pure water.
Protective equipment: Clean suits, gloves, masks (if operating in a clean area, the protection level of that area must be met).
Environmental and equipment preparation
Choose to replace it during non-production periods to avoid affecting normal use.
Turn off the power supply of the transfer window and ensure that the fan, ultraviolet lamp, and other equipment stop running.
If the transfer window is located in a clean area, the surrounding environment should be cleaned and disinfected (such as wiping the floor and walls with alcohol). If necessary, local clean air conditioning should be turned on to maintain a positive-pressure environment.
Ii. Replacement Steps (Taking the common “Top/Back Mounted Filter” as an example)
Disassemble the old filter.
Open one side door of the transfer window (depending on the installation position of the filter, the decorative panel or inspection door may need to be removed), and clean the frame around the filter with a lint-free cloth dipped in alcohol to remove surface dust.
Loosen the fixing device of the filter: If it is a snap-on type, simply pull off the snap-on. If it is fixed by screws, use a screwdriver to remove the screws (note to sort and store the screws properly to avoid loss).
Carefully remove the old filter to avoid shaking or tilting (to prevent the contaminants trapped inside from scattering). Immediately seal it in a sealed bag (tie the bag tightly) and dispose of it as hazardous waste (especially in scenarios such as pharmaceuticals and biological laboratories).
Clean the filter installation frame.
Thoroughly wipe the surface and gaps of the installation frame with a lint-free cloth dipped in alcohol to remove any remaining dust, sealant, or stains.
Check if the frame is deformed or rusted. If so, it needs to be repaired first (such as adjusting the flatness), otherwise it will cause the new filter to seal poorly.
Install a new filter.
Open the outer packaging of the new filter (keep the inner clean packaging and remove it as the last step before installation), and inspect the appearance of the filter: the filter paper is undamaged, the sealing rubber strip is intact, and the frame is not deformed.
Place the filter according to the airflow direction of the filter (usually marked with an “Airflow” arrow, which should be consistent with the airflow direction inside the transfer window, that is, the arrow points to the inside of the transfer window), ensuring that it is centered and closely attached to the frame.
Fixed filter: If it is a snap-on type, fasten the snap-on tightly (to ensure uniform force distribution). If it is fixed by screws, tighten the screws in diagonal order (to avoid deformation of the filter due to excessive tightening on one side). The force should be such that the filter does not loosen and there are no obvious gaps.
Seal inspection and reinforcement
Gently push the edge of the filter with your hand to make sure it is not loose. Observe the fit between the filter and the frame. If there are any tiny gaps, you can stick special sealing tape (width ≥10mm) along the edge to ensure there is no air leakage without any gaps.
If the transfer window is equipped with a pressure strip, the pressure strip needs to be reinstalled to press the edge of the filter tightly and enhance the sealing performance.
Iii. Verification and Closure after Replacement
Appearance and function inspection
Close the transfer window door, connect the power supply, start the fan (if any), and observe whether the filter has any abnormal vibration or abnormal noise.
Touch the periphery of the filter with your hand to feel if there is any air leakage (if there is obvious air flow, it indicates that the seal is not tight and the fixation condition needs to be rechecked).
Differential pressure monitoring and recording
Start the transfer window fan. After it operates stably (about 10 to 15 minutes), record the initial pressure difference (the resistance value of the new filter) as the benchmark for subsequent monitoring.
If conditions permit, a scanning leak detection can be carried out (such as using a PAO aerosol generator) to ensure that there are no leakage points in the filter.
Cleaning and resetting
Use a lint-free cloth dipped in alcohol to wipe the interior of the transfer window to remove any dust that may fall off during the replacement process.
Organize the tools, clean up the site, and dispose of the old filters as per regulations (do not discard them at will).
Fill in the replacement date, filter model, initial pressure difference, and other information in the equipment maintenance record form to facilitate subsequent traceability.
Iv. Precautions
Avoid contamination: During the replacement process, the operator must keep their hands clean (wear gloves) and avoid touching the filter paper of the filter (to prevent fingerprints from clogging the filter material or introducing contaminants).
Compatibility: It is essential to use a filter that matches the transfer window (with the same size and frame type), otherwise it may lead to unstable installation or poor sealing.
Special scenario requirements: In A/B grade clean areas (such as pharmaceutical sterile workshops), replacement must be carried out in a sterile environment. If necessary, laminar flow protective covers should be used to ensure that the entire operation is sterile.
Through a standardized replacement process, it can be ensured that the filter achieves the best purification effect, avoiding the risk of decreased cleanliness or cross-contamination caused by improper installation.