How to configure ULPA front-end pre-filtering?

ULPA is positioned as terminal fine filtration, and the filter section in front of it should intercept most of the load. Whether the pre-filtration configuration is appropriate or not directly determines how long the terminal filter element can be used and whether the system resistance will be out of control.

The configuration plan is not determined according to a fixed formula, but must be derived from the air intake conditions. Fresh air or circulating air, dust content, particle size distribution, whether there is oil mist, and how long the operation time is - these are determined, and only then can the pre-filtration stages, form and replacement cycle be based.

Fresh air and circulating air cannot be configured in the same set

This is one of the first things to understand when configuring pre-filtering.

Fresh air : introduced directly from the outdoors, and the dust content changes with the season, region, and surrounding environment. Spring pollen, winter haze, and dust around industrial areas will all affect the front-end load. The pre-filtration of the fresh air system should be designed according to the most unfavorable conditions, or room for adjustment should be reserved.

Circulating air : Returning from the clean room, the dust content is relatively stable. However, if there are dust-producing and dust-generating equipment in the process, specific particles may be entrained in the return air. The pre-filtration configuration of the circulating air system must be combined with the characteristics of the process and cannot simply copy the fresh air scheme.

Mixed air : Fresh air plus return air is a common configuration. The dust content and composition of the two air flows are different. The pre-filtration must consider the loads on both sides at the same time. When using MAU or other centralized treatment units, you should also check the sealing and maintenance accessibility of each filter section - if the sealing is not good or replacement is inconvenient, the front-stage protection effect will be compromised.

Configuration does not only look at the filtering level

When selecting the pre-filter, the filtration level is only one of them.

Effective filtration area : The area of ​​the front-stage filter is insufficient, the wind speed is high, the dust holding capacity decreases, and replacement will be frequent. The combination of area and level should match the actual load.

Rated air volume : Check the resistance at the system design air volume. Do not just look at the superscript value in the sample. When multi-stage filtration is connected in series, the resistance of each stage must be confirmed separately.

Replacement space : The front filter is usually replaced more frequently than the end filter, and replacement channels and maintenance space must be set aside during the design stage. If the front stage is installed in a position that requires disassembly of other components to replace it, actual maintenance can easily be delayed, and the protection effect will be impossible to talk about.

Sealing status : If the front-stage filter is bypassed or installed incorrectly, even if the level is selected correctly, dusty air may bypass it and directly hit the end. For troubleshooting ideas for this type of problem, please refer to the instructions on whether the filter body is qualified but the system is leaking air.

How to divide the load at each level

There is usually more than one level of pre-filtration. How to distribute the load affects the replacement cycle of each section and the total resistance of the system.

The primary effect bears the largest particle load and intercepts coarse particles and fibers. Maintenance frequency at this level is the highest and replacement costs are relatively controllable.

The medium efficiency further reduces the concentration of fine particles, allowing the air entering the end to reach the conditions where ULPA can work stably for a long time.

The terminal ULPA is responsible for the final fine filtration. Its replacement cycle should be relatively long. If the ULPA is replaced frequently, it usually means that the front-end protection is not in place, not that there is a problem with the ULPA itself.

The principle of division of labor at all levels is: let each level bear the load it is good at. The more you do on the front end, the more stable the end will be for a longer period of time.

The total resistance must be calculated together

Adding a pre-filter section will change the total resistance of the system, which must be clearly calculated before confirming the configuration plan.

List the initial resistance and final resistance of each level of filter separately, add them up to the total resistance of the system, and then compare it with the fan performance curve to confirm whether the operating point is acceptable under the design air volume. It also depends on whether the fan still has margin when the filter element accumulates dust and reaches the final resistance. Supporting FFU fan filter unit system, the unit capacity must match this set of resistance; equipment-side applications such as The EFU equipment-side fan filter unit has a compact internal space, leaving less room for adding filter sections, and more room needs to be left during accounting.

Selecting the fan only based on the initial resistance and ignoring the increase in resistance in the later period is a common oversight when configuring pre-filtration.

How to do operation management

The completion of pre-filtering configuration is just the beginning, and operation management determines whether it can continue to function.

Record the pressure difference at each level separately . The working status of the filters at each level is different, and it is impossible to determine which level needs maintenance by mixing the records together.

Set replacement cycles individually . The replacement basis for initial effect, medium effect and terminal effect is different and cannot be processed according to the same cycle. If the front stage is replaced frequently but the reason is not recorded, it is impossible to determine whether the load exceeds expectations or the product is improperly selected.

Recheck the air volume after upgrading the front stage . After adding or replacing the pre-filter section, the system resistance may change. If the total resistance increases and the end air supply decreases, it needs to be readjusted instead of simply increasing the fan gear.

Keep records of replacements . The degree of dirtiness of the replaced front-stage filter and changes in replacement cycles are all references for judging the upstream pollution load. involving For HEPA/ULPA air filter products of different levels, the testing requirements and replacement basis for each level should also be clearly stated in the maintenance documents.

Project judgment example

During the peak dust season in the fresh air section, ULPA is frequently replaced.

Don’t rush to change to a higher grade ULPA yet. Check the actual status and maintenance records of the front-stage filter: If the replacement cycle of the primary and medium-efficiency filters is too long or has failed, it means that the front-stage protection is not in place and the load is directly pressed to the end. The adjustment direction is to resume front-stage maintenance and increase the number of pre-filtration stages when necessary, rather than letting ULPA bear a load that does not belong to it.

If the front-stage maintenance is normal, then evaluate whether the dust content in the fresh air exceeds the original design conditions, and adjust the pre-filtration configuration if necessary.

Selection and Acceptance Checklist

About Aili Industrial’s pre-filtration package

The prerequisite for pre-filter configuration is to understand the air intake conditions and load distribution. The more complete this information is, the more targeted the selection and division of labor at all levels of filters will be.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide ULPA ultra-high efficiency filters and supporting filtration products of different grades. For projects that require multi-stage filtration, the specifications, resistance and replacement methods of each stage can be checked together during the planning stage to allow the terminal ULPA to operate under appropriate working conditions.

When enquiring, provide the air intake source, dust content, operating time and existing filter section configuration, which will help determine the pre-filtration solution. The specific configuration is subject to the technical documents and operating data confirmed by the project.