What are the other reasons for the sudden surge in resistance of high-efficiency filters?

A sudden surge in the resistance of a high-efficiency filter (exceeding the final resistance by more than 20%, such as a sudden increase from 400Pa to 500Pa) may be caused by various abnormal factors. Besides the basic clogging of the filter material, it is also necessary to investigate the dimensions of system operation, installation and maintenance, and environmental changes. The following are the common causes and countermeasures:
1. The pre-filtering system has failed
The pre-filter (primary/medium efficiency) was not replaced in time
Principle: The pre-filter is responsible for intercepting large particle contaminants (such as dust and hair). If it is not replaced for a long time, the high-efficiency filter will directly bear the load at the front end, accelerating clogging.
Troubleshooting method:
Check whether the resistance of the pre-filter exceeds its final resistance (usually 200-250Pa for the primary efficiency and 300-400Pa for the medium efficiency).
Observe the appearance of the pre-filter. If the filter material turns black and the dust accumulation thickness exceeds 5mm, it indicates that it has failed.
Solution: Replace the pre-filter immediately. If necessary, shorten the replacement cycle of the pre-filter (for example, from 3 months to 1 month).
2. The pre-filter is installed incorrectly or leaks
Phenomenon: The sealing strips of the pre-filter frame have fallen off, and the filter material has not been aligned with the frame, causing a "short circuit" in the airflow. The upper-filtered air directly impacts the high-efficiency filter.
Troubleshooting method: Use the smoke method to detect whether there is smoke leakage upstream and downstream of the pre-filter (especially at the joints of the folded filter material).
Solution: Reinstall the pre-filter, replace the aged rubber strips, and ensure a tight seal.
Ii. Abnormal system operation
1. Fan malfunction or improper adjustment of air volume
Fan overload/speed increase
When the belt of the fan becomes loose and slips, the motor will automatically increase its speed to maintain the air volume, resulting in a sudden increase in the wind speed passing through the high-efficiency filter and an instant rise in resistance.
Troubleshooting: Measure whether the current of the fan exceeds the rated value and listen for any abnormal sounds (such as howling) during the fan's operation.
Frequency conversion system failure
A malfunction of the frequency conversion controller may cause the fan to suddenly increase its speed, with the air volume exceeding the designed value by 120%, forcing the high-efficiency filter to bear an excessive load.
Troubleshooting: Check the parameter Settings of the frequency converter and compare the actual air volume with the designed air volume (a measured air volume hood can be used).
Solution: Inspect and repair the fan and the frequency conversion system, and calibrate the air volume to the designed value (such as 0.45m/s±20%).
2. Sudden blockage of pipelines or valves
Common scenarios:
Foreign objects (such as tools or screws) in the air duct get stuck in the regulating valve, causing a sudden decrease in the downstream air volume and pressure accumulation upstream of the high-efficiency filter.
Fire dampers and check valves close due to misoperation or rust, creating a "back pressure" that acts on the filter.
Troubleshooting method:
Check whether there is any abnormal noise or vibration at each node of the pipeline (especially at elbows and valves).
Compare the pressure difference before and after the high-efficiency filter with the total pressure difference of the system. If the proportion of the former suddenly increases (for example, from 50% to 80%), it may be due to pipeline blockage.
Solution measures: Shut down the machine to clear foreign objects in the pipeline, and repair or replace the faulty valve.
Iii. Issues with the filter itself
The filter material is damaged or the structure has collapsed
Reason:
During transportation/installation, the filter paper was hit, causing the pleated area to break (commonly seen in foldable high-efficiency filters).
Under long-term high-humidity conditions, the filter material gets damp, softens, and adheres, and a "dense layer" forms locally, hindering the airflow.
Troubleshooting method:
The aerosol leak detection method is used to detect whether there is any leakage downstream. (In the PAO test, when the particle concentration downstream is greater than 20 particles/L, it is judged as damage.)
Remove the filter to observe the filter material. If through holes, large-scale collapses, or mold spots are found, it needs to be replaced immediately.
Note: In biosafety scenarios, damaged filters may release contaminants and should be treated as hazardous waste to avoid direct contact.
2. The sealant ages and cracks
Phenomenon: The polyurethane or silicone rubber on the filter frame develops cracks due to high temperature and oxidation. The airflow rapidly erodes the edge of the filter material through the gaps, causing a sharp increase in local resistance.
Troubleshooting method: Shine a flashlight on the side of the filter frame to observe if there are any hair-like cracks or bulges in the rubber layer, especially at the stress concentration points at the four corners.
Solution: If the crack length exceeds one-third of the perimeter of the frame, the entire filter needs to be replaced. If it is a local small crack, it can be temporarily repaired with sealant, but the next inspection cycle needs to be shortened.
Iv. Sudden environmental Changes
1. Short-term high-pollution impact
Scene:
Outdoor dusty weather (such as sandstorms) and temporary welding/grinding operations in workshops have led to a sudden increase of more than ten times in dust content.
The cleanroom was opened for too long and the self-cleaning system was not turned on, causing a large amount of unfiltered air to flood in.
Impact: The high-efficiency filter retains excessive dust within several hours, and the resistance increases linearly and rapidly (for example, by 20-30Pa per hour).
Countermeasures:
Temporarily close the fresh air valve and activate the return air system to maintain the internal circulation.
After the pollution ends, if the resistance does not exceed 90% of the final value, it can be observed for 1-2 days. If the resistance stabilizes and no longer rises, it can be temporarily not replaced. If it keeps rising, it needs to be replaced.
2. Chemical corrosion or adhesion of sticky substances
Chemical corrosion
The presence of acidic gases (such as SO₂, HCl) or disinfectants (such as ozone) in the environment can erode the filter material fibers over a long period of time, causing the fibers to break and engage with each other, forming "lumps" that impede the airflow.
Characteristics: The resistance increases, accompanied by the filter material becoming brittle and yellowish, and even breaking at the slightest touch.
Viscous substance
Oil mist, glue mist, and other contaminants adhere to the surface of the filter material, forming a sticky layer (similar to "oil sludge"), which leads to a sharp drop in air permeability.
Scene: Food processing workshop (fume), spraying line (paint particles), laboratory (organic solvent evaporation).
Solution:
In a chemically corrosive environment, use corrosion-resistant filter materials (such as PTFE material) instead.
In a viscous environment, add a pre-oil removal filter (such as a glass fiber mat primary filter + activated carbon filter), and regularly clean the pre-filter layer with a dedicated solvent.
V. Human operational errors
1. Incorrect cleaning or maintenance
Prohibited behavior:
"Blowing" or "washing" the high-efficiency filter may cause the filter material fibers to fall over, the structure to be damaged, and the local resistance to increase sharply.
Pry the filter frame with a sharp tool (such as a screwdriver) to cause the sealant to crack.
Troubleshooting: Inquire about the recent maintenance records. If there is any improper operation, physical damage to the filter should be inspected first.
2. The system was not re-debugged after the transformation
Scene:
The addition of new equipment led to changes in the air duct layout or the replacement of higher-power fans without recalculating the filter load.
Consequence: The actual air volume exceeds 150% of the designed air volume of the filter, and the resistance increases exponentially (the resistance is proportional to the square of the air velocity).
Solution: Re-conduct the system air volume balance adjustment. If necessary, replace it with a larger-sized high-efficiency filter (such as increasing the filtration area).
Vi. Emergency Response Procedures
Stop the machine immediately: To prevent the filter material from cracking or the fan from overloading due to a continuous increase in resistance.
Quick troubleshooting:
Check the resistance of the pre-filter, the operating parameters of the fan, and the status of the pipeline valves within 5 minutes.
Complete smoke leakage detection or particle concentration detection within 30 minutes to locate the leakage point or damage location.
Graded processing
Mild abnormality (resistance increase < 30%): If the pre-filter fails, observe for 2 hours after replacing the pre-filter. If the resistance decreases, there is no need to replace the high-efficiency filter.
Severe abnormality (resistance increase > 50% or leakage detected): Immediately replace the high-efficiency filter and disinfect/clean the surrounding environment (in a biosafety scenario).
Record and archive: Write the cause of the anomaly and the handling process into the maintenance log as a reference for subsequent preventive maintenance (such as increasing the frequency of pre-filter checks).
Summary: The "Three-dimensional Troubleshooting Method" with Soaring Resistance
Key typical tools for dimensional screening
The pre-filtering system includes the resistance of the pre-filter, installation sealing performance, dust holding capacity differential pressure gauge, and smoke generator.
The system operation fan current, air volume, pipeline valve status anemometer, multimeter
The filter material of the filter body is damaged, the sealant is aged, and there is corrosion/viscous contamination of the particle counter. Visual inspection
Through systematic investigation, the root cause of the soaring resistance can be quickly identified, avoiding excessive replacement or delayed maintenance due to misjudgment, and ensuring the stable operation of the clean system. For scenarios where abnormal resistance frequently occurs, it is recommended to install an online resistance monitoring and alarm system (such as an automatic alarm when the set resistance exceeds the final value by 10%) to achieve preventive maintenance.