What are the installation and disassembly methods of the laminar flow hood HEPA filter?

The installation and disassembly of laminar flow hood high-efficiency filters must follow strict clean operation norms to avoid contamination risks and ensure filtration efficiency. The following are detailed operation steps and precautions, applicable to laminar flow hood equipment in most cleanroom/laboratory scenarios:
I. Preparations before installation
Personnel and environment preparation
Personnel protection: Wear dust-free suits, shoe covers, gloves, masks, and goggles if necessary to ensure that no hair or dander is exposed all over the body.
Environmental cleanliness
Start the laminar flow hood pre-filtration system 30 minutes in advance to purify the air in the operation area.
Wipe the laminar flow hood frame, installation interface, and surrounding areas with 75% ethanol or a special lint-free cloth to remove dust and particles.
2. Tool and material preparation
Tools: Dust-free tweezers, torque wrench (if fastened with bolts), explosion-proof screwdriver, leakage detector (such as PAO detector).
Materials: New high-efficiency filter (model, size, and filtration efficiency grade, such as H14, need to be confirmed), sealant (silicone rubber or polyurethane), dust-free gasket, alcohol cotton pad.
3. Filter inspection
Before unpacking, make sure the packaging is intact without any signs of damage or moisture.
After unpacking, check the appearance of the filter: the filter material is not deformed or damaged, the frame is free of burrs, the sealing rubber strip is intact, and the label information (model, production date, test report) is complete.
Ii. Disassembly Steps of High-Efficiency Filters (Taking Vertical Laminar Flow Hood as an Example)
Shutdown and safety confirmation
Turn off the power supply of the laminar flow hood fan, hang the "Under Maintenance" warning sign, and ensure that the equipment is in a power-off state.
If it is a negative-pressure laminar flow hood, the exhaust system should be turned on first to maintain a slight negative pressure inside the hood and prevent the spread of contaminants during disassembly.
Remove the old filter.
Loosen the fixing device: Unscrew the fixing bolts of the filter frame in a diagonal sequence (if it is a snap-fit type, gently lift the snap-fit) to avoid deformation of the frame caused by unilateral force.
Remove the old filter: Use dust-free gloves to support the bottom of the filter and slowly take it out vertically upwards, avoiding tilting (to prevent dust from falling).
Temporary sealing interface: After removing the old filter, immediately cover the installation interface with a lint-free cloth to prevent outside air from entering.
Interface cleaning and inspection
Wipe the surface of the installation frame with alcohol cotton pads to remove the residual sealant, dust, and particles.
Check the flatness of the frame. If there is any deformation or scratch, it should be repaired or replaced in time to avoid affecting the sealing of the new filter.
Iii. Installation Steps of High-Efficiency Filters
Positioning and alignment
Gently place the new filter above the installation interface, adjust the direction (note the arrow marking, usually "upward" or "airflow direction" points to the air supply side), and ensure that the frame is completely aligned with the frame.
For pleated filters, it is necessary to confirm that the folding direction of the filter material is perpendicular to the direction of the airflow (for example, the filter material of a vertical laminar flow hood should be folded horizontally, and the airflow should be vertically downward).
Fixation and sealing treatment
Bolt fixation: Tighten the bolts in a diagonal sequence in several steps, with uniform force each time (refer to the torque value in the equipment manual, usually 5-8N · m), to avoid excessive local pressure that may damage the filter material.
Sealant treatment: Evenly apply a sealant (about 2-3mm thick) at the joint between the filter frame and the frame to form a continuous sealing line without bubbles or breaks.
Sealing gasket installation: If sealing gaskets are used, it is necessary to ensure that the gasket material is intact and undamaged and that the edges are closely attached to the frame to avoid misalignment.
Preliminary inspection and startup test
Check whether the filter is installed firmly, the frame is not loose and the sealant is not overflowing.
Connect the power supply, turn on the fan to the rated wind speed, and observe whether there is any shaking or abnormal sound on the surface of the filter (it may be due to uneven installation).
Iv. Leakage Test after Installation (Key Step)
PAO aerosol Testing (Common Methods)
Aerosol occurrence: Inject PAO aerosol (with a particle size of about 0.3μm) upstream of the filter (on the air intake side of the fan), and maintain the concentration at 10-20μg/L;
Downstream detection: Use a particle counter to scan along the surface of the filter and the seam of the frame at a distance of approximately 2-3cm, with a scanning speed of ≤5cm/s.
Qualified standard: Downstream particle concentration ≤0.01μg/L (i.e., filtration efficiency ≥99.99%), no significant increase in particle concentration at the seam of the frame (leakage rate ≤0.01%).
Airflow velocity test
Measure the wind speed at multiple points in the working area of the laminar flow hood with an anemometer (such as a nine-square grid layout). The average wind speed should be within the range of 0.36-0.54m/s, and the wind speed deviation at each point should be no more than 20%.
V. Precautions for Disassembly and Installation
1. Operational taboos
It is strictly forbidden to touch the surface of the filter material with bare hands to avoid contamination of the filter material by sweat and grease.
During the installation process, it is strictly prohibited to forcefully squeeze or impact the filter to prevent damage to the filter material or deformation of the frame.
In a humid environment (humidity > 60%), operations should be postponed to prevent poor curing of the sealant or moisture absorption of the filter material.
2. Safety protection
If the old filter may come into contact with contaminants (such as microorganisms, and harmful dust), the surface of the filter should be disinfected (sprayed with 75% ethanol or fumigated with formaldehyde) before disassembly, and a gas mask should be worn.
The disassembled old filters should be put into sealed bags and treated as hazardous waste. They must not be discarded at will.
3. Special scene handling
Horizontal laminar flow hood: When installing, it should be noted that the self-weight of the filter may cause sagging, and additional support parts (such as metal brackets) need to be used for fixation.
Explosion-proof area: Use explosion-proof tools to avoid generating static electricity or sparks. Before installation, test the concentration of flammable and explosive gases in the environment.
Vi. Common Problems and Solutions
Possible causes and solutions for problem phenomena
If the leakage test is not qualified, the sealant is not evenly applied or there are bubbles. Clean the interface again, reapply the sealant, or replace the gasket
If the wind speed is abnormal and the filter is installed in the wrong direction, stop the machine and adjust the direction of the filter to ensure that the airflow is marked correctly
After installation, if the force on the fixing bolts is uneven, retighten the bolts in a diagonal sequence
The frame seepage sealant has not fully cured or has been exposed to moisture, which prolongs the curing time (usually 24 hours). Operate in a dry environment
Summary
The installation and disassembly of laminar flow hood high-efficiency filters are key links in maintaining a clean environment. The core lies in strictly controlling the risk of contamination and ensuring the reliability of sealing. When operating, the standardized process of "preparation - disassembly - cleaning - installation - testing" should be followed. At the same time, the details (such as explosion-proof and anti-corrosion requirements) should be adjusted in combination with the equipment model and usage scenarios. It is recommended to conduct visual inspections of the filter installation status every quarter and carry out a comprehensive leakage test at least once a year to ensure the long-term efficient operation of the laminar flow hood.