How to check if the cleanliness is not up to standard after replacing the filter?
After replacing the HEPA, a retest found that the cleanliness was not up to standard, which was a difficult situation in operation and maintenance. The most common judgment at this time is 'the new filter element is not efficient enough'. But this conclusion is too early.
Direct answer: First confirm that the test status is consistent with the original acceptance conditions, and then separately check the filter seal, actual air supply volume, air flow organization and on-site pollution sources. It cannot be immediately concluded that the new filter element is not efficient enough.
Step one: Check filtration and air supply first
Check the grade, installation direction, serial number and on-site leak detection record of the new filter element; measure the actual air volume and local surface wind speed to confirm that the resistance change after replacement does not push the fan operating point away from the target range.
The key to this step is whether the comparison is in the same operating gear before and after replacement. If the resistance of the new filter element is different from that of the original filter element, and the fan gear has not been adjusted, the air supply volume may have deviated from the original design value, and the cleanliness will naturally be affected. Supporting In the case of FFU fan filter unit , it is recommended to measure the wind speed on a single table first, and then determine whether the unit gear needs to be adjusted.
Step 2: Look at the room operating conditions again
The entry of people, equipment, and materials may change dynamic particle levels; blocked return air vents, air leaks through door gaps, and local airflow short circuits may also affect the results.
Determine whether the problem is concentrated in a single air supply outlet or the entire area based on the distribution of measuring points. If only one If there is an abnormality under the HEPA/ULPA air filter , the scope of troubleshooting can be narrowed to the unit and its interface; if multiple locations are abnormal at the same time, the total air volume and return air path of the system should be reviewed instead of replacing the filter elements one by one.
Step 3: Form a repeatable adjustment plan
After adjusting the air volume, repairing the interface or controlling the pollution source, retest under consistent operating conditions.
Record the parameters before and after each treatment to avoid multiple variables changing at the same time and making it impossible to determine effective measures. Device-side applications such as For the filter inside the fan filter unit at the EFU equipment end , when retesting, it should also be confirmed that the equipment itself is in normal production or debugging status, otherwise the measured local wind speed will not be comparable.
Step 4: Partition analysis of measurement point results
If the non-compliance is only concentrated under one air supply outlet, check the filter element and air flow path of that unit first. If multiple locations are abnormal at the same time, review the total air volume, return air, construction residue and personnel operations of the system.
Conducting investigations by region instead of just by a single filter element is more conducive to narrowing down the cause. For the position of the liquid tank sealing structure, if there are abnormalities in the four corners after replacement, please refer to Interface instructions for liquid tank seal HEPA check the blade edge and tank body; use For the location of the ULPA ultra-high efficiency filter , the testing data and on-site leak detection requirements should be rechecked according to the corresponding level.
quick checklist
project |
Confirmation method |
Abnormal measurement point distribution |
Determine single point or entire area |
Air volume before and after replacement |
Actual measurement comparison at the same gear |
On-site leak detection |
Execute and mark according to project plan |
Room operating status |
Record the status of personnel, equipment and materials |
Application background and judgment boundaries
A single abnormal signal usually cannot directly locate the HEPA fault. It is recommended to compare the particle count, air volume, pressure difference, leak detection and fan control records on the same timeline. First find out the area and time when the change occurred, and then arrange targeted inspections.
Failure to meet cleanliness standards and whether the filter itself is qualified are two issues that need to be verified separately. The former involves system operating status, while the latter has factory testing data to correspond to. Mixing the two things together and discussing them will make it easy to go back and forth in the direction of investigation.
About Aili Industrial’s post-replacement troubleshooting support
Aili Industry covers the production of filters, fans and air supply equipment, and can help troubleshoot problems by comparing filter resistance, sealing and air volume of the entire machine. The processing results should be confirmed by on-site re-testing.
Aili Industrial produces HEPA/ULPA filters and supporting FFU fan filter unit , EFU and high-efficiency air supply outlet. When the filter and air supply equipment are matched in the same system, the matching relationship between the filter element resistance and the fan operating point can be checked uniformly before leaving the factory to reduce air supply deviations caused by resistance changes after replacement. For occasions such as semiconductors and pharmaceuticals that require high particle control, it is recommended to archive replacement records, leak detection results and retest data together.
