How to choose U15, U16 and U17 filters?

Putting these three levels together, it is easiest to simplify it into 'the bigger the number, the better'. When it comes to actual selection, things are not that simple.

The difference between U15, U16, and U17 is the proportion of penetration allowed under specified test conditions. According to the common classification of EN 1822, the lower limit of the overall efficiency of MPPS (the most easily penetrable particle size) among the three increases in turn. This means that the higher the grade, the fewer particles are allowed to pass through.

But grade is only one input for selection. It does not automatically solve air leakage, pollution sources or airflow organization problems. A U17 that is not properly sealed may not be as effective as a U15 that is well sealed. This point has been mentioned repeatedly in the previous articles, and you still need to confirm it again when selecting.

First unify the grade evaluation caliber

Before comparing the three levels, first confirm whether everyone is talking about the same set of standards.

Grade markings under different standards may not be directly interchangeable. Standard systems such as EN 1822 and ISO 29463 have different classification methods for high-efficiency filters, and the labeling methods are not exactly the same. If it says 'U16 required' in the procurement document, it is best to indicate the standard version and test method at the same time.

Overall efficiency and local efficiency should be looked at separately. Ratings usually correspond to overall efficiency, but the determination of local leak detection is a different set of requirements. Only if both data are qualified can the product be complete. For the implementation method of specific testing items, please refer to the relevant instructions of ULPA factory testing.

The test particle size should be clear. Is it MPPS efficiency or the efficiency of a certain fixed particle size? The two cannot be mixed. MPPS itself is not a fixed value, it is related to the filter material and air flow conditions. For details, please refer to the relevant instructions of MPPS.

Consider resistance along with equipment capabilities

As the level increases, the resistance usually changes - but doesn't necessarily increase linearly.

For products of the same size and structure, the resistance of U16 is generally higher than that of U15. If the system fan margin is insufficient, the air volume may decrease after the upgrade, and the actual air supply effect will become worse.

The difference in resistance between products may be greater than the difference in grade. A well-designed U16 may have lower resistance than another poorly designed U15. When comparing, use data under the same air volume, and check the effective filtration area and filter material type. For specific comparison methods, please refer to the relevant description of the relationship between efficiency and resistance.

The final resistance condition must also be taken into account. After the filter element has been running for a period of time, the resistance will rise. Whether the fan still has margin under the final resistance determines how long the filter element can be used and whether the air volume will decrease.

When is a higher level required?

Grade selection should be driven by process requirements, not 'the higher, the safer'.

Situations that require a higher level:

• The process is particularly sensitive to particles of certain particle sizes and the penetration level of U15 may not be sufficient

• Project acceptance criteria clearly require reaching a certain level

• The control objectives of the protected area are stricter than those of general clean rooms

Situations that do not necessarily require a higher level:

• The system itself has air leakage or airflow organization problems, and there is limited improvement by upgrading the level.

• The source of pollution is within the protected area and the particles are generated after filtration

• Insufficient air volume is currently the main bottleneck, and upgrading the filter element may exacerbate the problem.

Different process areas can have different requirements. Use U16 for key workstations and U15 or HEPA for general areas. This zoning configuration is reasonable. There is no need to upgrade all locations simultaneously.

Confirmed by installation verification

After the level is selected, the final judgment criterion is the actual performance after installation.

Air volume measurement : Confirm that the actual air supply volume is within the design range, and confirm one by one when multiple terminals are connected in parallel.

On-site leak detection : Scan the filter material surface and interface according to the project plan. The higher the level, the more sensitive it is to local leakage. The detection method and judgment standard must correspond.

Area test : Whether the particle concentration in the protected area meets the design requirements. This item does not have a one-to-one relationship with the filter grade, and is also affected by air flow organization, pollution sources and operation management.

involving Products of different grades of HEPA/ULPA air filters have the same verification methods, and the criteria are implemented according to corresponding standards. Supporting FFU fan filter unit system, the matching of fan operating point and filter element resistance must also be checked; equipment-side applications such as The EFU equipment-side fan filter unit has a compact internal space and few available solutions, so you need to leave room for selection.

Project judgment example

A certain device originally used U15, but after process adjustments, it was considered to be upgraded to U17.

There are several things to confirm before upgrading: whether the existing fan can maintain the target air volume under the resistance of U17; whether the installation space allows the thickness or structure of U17; whether the sealing structure needs to be adjusted accordingly; whether the on-site leak detection methods and instruments meet the detection requirements of U17.

If these conditions are met, you can configure it according to U17. If the air volume margin is insufficient, it may be necessary to adjust the fan or box together instead of just replacing the filter element. If the project only states the room cleanliness level and does not specify local process requirements, U17 should not be selected for all terminals by default.

Selection and Acceptance Checklist

About Aili Industrial’s ULPA grade selection and cooperation

The choice between U15, U16 and U17 is essentially a matching issue between 'process requirements' and 'system capabilities'.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide ULPA ultra-high efficiency filter and supporting air supply equipment. Different grades of products are available with FFU fan filter unit and EFU matching confirmation, filter element resistance and fan operating point can be calculated together in the planning stage.

Providing particulate control targets, design air volume, available static pressure and installation conditions with your inquiry will help confirm the appropriate grade and configuration. Specific performance is subject to the testing data of the corresponding model.