If the cleanliness is not up to standard, should I upgrade the ULPA or make rectifications first?

If the cleanliness test fails to meet the standard, the first reaction is often 'the filter element grade is not enough'. Sometimes this judgment is correct, and sometimes it leads to a wrong direction.

Upgrading ULPA is to improve the filter penetration control capability. It cannot solve the problem of air leakage, dust generation and air flow short circuit. If the problem lies in these links, replace the filter element with a higher grade, and the test results may still be unqualified. It is more effective to first understand the source of substandard filters and then decide whether to upgrade them than to directly replace the filter element.

Don’t be in a hurry to upgrade yet, decide according to the symptoms.

If the test is not up to standard, look at the abnormal distribution first.

If abnormalities are concentrated near the edge of the filter, box seams or access openings , first suspect air leakage in the seal and bypass. This type of problem belongs to the integrity of the installation and has nothing to do with the grade of the filter element.

If the abnormality is concentrated inside a certain workstation or equipment , and the air outlet test is normal, give priority to checking whether there are dust sources in this area and whether the airflow is blocked.

If the entire area is generally high , check the air volume, number of air changes and return air path first, and then consider the filtration level.

If only a few measuring points are abnormal and their locations are not fixed , the influence of sampling methods, instrument status and personnel operations must be eliminated. The test conditions themselves are unstable and the data cannot be used as a basis for decision-making.

involving To judge the integrity of HEPA/ULPA air filters , you should look at the on-site leak detection records together, and you cannot rely solely on the particle count results to infer the filter element grade.

Leakage investigation should cover the complete air supply path

The factory inspection of the filter only proves that the product body is qualified. The installed system also includes the frame, sealing gasket, box seams and inspection openings. Air may bypass the filter material from these interfaces and directly enter the clean side.

It is recommended to cover during investigation:

Filter material surface. Scan the filter paper and pleats for tears or pinholes.

The junction between filter material and frame. Check whether the glue filling line is continuous and whether the glue is cracked or detached.

The sealing surface between the frame and the mounting frame. The compressed state of the gasket or the mating state of the liquid tank is a high-risk location for air leakage on site. For the verification method of the liquid tank structure, please refer to the instructions related to the knife edge size.

Box connection. Seams, flange surfaces, and access doors may all become bypasses.

Pipes and other openings. Unsealed holes and places where cables pass through walls are also easily overlooked.

If abnormality is found during leak detection, locate it first and then deal with it. Do not repair the filter paper without positioning it, and do not replace the filter element if the interface problem is not solved. Supporting FFU fan filter unit system, the interface between the unit and the ceiling should also be included in the scope of inspection; equipment-side applications such as The EFU equipment-end fan filter unit has a compact internal structure, and the interface accessibility needs to be confirmed during the planning stage.

Airflow and dust production should also be looked at together

There is no problem with the seal and the filter element is qualified, but the cleanliness may still not be up to standard. At this time, the focus turns to airflow organization and pollution sources.

Insufficient air volume. If the number of air changes or unidirectional flow coverage is insufficient, the efficiency of particle dilution and removal will be low. Compare the actual measured air volume with the design value to confirm whether it is within the design range.

Airflow short circuit or eddy current. Incomplete coverage of the air supply surface, unreasonable position of the return air outlet, and obstruction of equipment or structural parts may form local stagnation areas. Particles accumulate in these areas, and the measurement point results are naturally higher.

The source of dust generation is within the protected area. Particles may be generated from equipment moving parts, transmission mechanisms, personnel operations, and material entry and exit. If particles are generated after filtration, increasing the filtration level will provide limited improvement. This is especially important for equipment-side applications. No matter how clean the EFU air supply is, it cannot stop the mechanical friction next to the workstation from continuing to generate dust.

Dynamic and static differences. Passing the static test does not mean passing the dynamic test. The impact of personnel, equipment and materials under production conditions should be reflected in the test plan.

When will we discuss upgrading again?

After checking for leaks, airflow and dust production, if these links are normal, it is time to discuss the filtration level.

The process requirements have indeed improved. The particle control objectives are more stringent than the original design, or the acceptance criteria specifically require lower penetration.

The system has margin support. Upgrading ULPA usually increases the resistance. Whether the fan can maintain the target air volume must be calculated based on the initial resistance and final resistance of the new filter element. For specific methods, please refer to the relevant instructions on resistance calculation.

The installation interface can match. The thickness, sealing structure and disassembly and assembly path of the new filter element must be compatible with the existing box or equipment. Don’t just look at length and width.

Leak detection conditions can keep up. ULPA's local leak detection requirements are more stringent than HEPA, and the on-site instrument range, aerosol conditions, and scanning methods must match the new level.

Re-verification is required after upgrading. Air volume, leakage detection and regional particle testing must be redone, and the data before the upgrade will be retained as a baseline for comparison. involving For the selection of ULPA ultra-high efficiency filter , please refer to the corresponding product information.

Project judgment example

The particle monitoring in a certain clean area continues to be high. It is initially judged that the end filter level is not enough, and it is planned to upgrade H14 to U15.

After investigation, it was found that there were multiple bypasses in the end seal, there was equipment blocking near the return air outlet, and people moved frequently during the test. If these three items are not solved, the effect of directly replacing U15 will not be ideal.

The processing sequence should be: first repair the seal, adjust the return air path or equipment layout, clarify the test status, and then retest. If the retest is still high and the system conditions are confirmed to be met, then evaluate whether the filtering level needs to be upgraded. Upgrading is the last step, not the first.

Selection and Acceptance Checklist

About Aili Industrial’s investigation and configuration cooperation

The investigation of substandard cleanliness often requires checking the data on filters, air supply equipment and system conditions.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide HEPA/ULPA products of different grades and supporting air supply equipment. Filter can be used with FFU fan filter unit、Check the installation interface and sealing method of the EFU equipment-side fan filter unit together to facilitate the determination of whether the problem lies on the product side or the system side.

Provide the distribution of abnormal measuring points, air volume records, leak detection results and equipment structure during inquiry or troubleshooting, which will help narrow the scope of the cause. The specific treatment plan is subject to on-site testing results and project acceptance conditions.