What should I do if fibers and particles appear downstream of ULPA?

If fibers or abnormal particles are found downstream of the filter, the first reaction is usually 'the filter element is broken.' This judgment may be correct, but by directly assigning responsibility to the filter element, the real cause will often be missed.

Fibers and particles appearing downstream may come from more than one source. The filter material itself, the protective screen, the box material, the seals, the residue from the installation process, and the dust generated by the downstream equipment are all possible. It was found that fibers do not necessarily come from the filter element and need to be located based on changes in morphology, position and operation. For specific troubleshooting ideas, please refer to the instructions related to overall and local efficiency.

Confirm sampling and distribution first

Before tracing the source, first confirm whether the thing collected is really abnormal.

Sampling location. Is it collected directly on the outlet surface of the filter, or is it collected at a downstream station or pipeline? Different locations may point to different sources. If it is collected directly below the air outlet surface, the filter element is more likely to be collected; if it is collected at the end of the pipe, the intermediate links may also contribute.

background level. What are the background particles in the test environment? Will the sampling process itself introduce contamination? Wiping materials, sampling containers, and operators may all be sources of contamination.

distribution characteristics. Are the abnormal particles concentrated in a certain location, or are they evenly distributed? Concentrated at a certain point, it points to local damage or air leakage at the interface; evenly distributed, it may be an overall problem or an upstream source. Comparing the sampling results at the center of the filter surface, at the edge and near the workstation can help narrow down the scope.

Appearance and composition. If there are conditions for morphological analysis, you can initially determine whether it is glass fiber, PTFE fiber, metal shavings or other materials. Fibers from different sources have different shapes and compositions. This step is not necessary, but it can reduce the blindness of the investigation.

Check filter element and structure

After sampling to confirm anomalies, the next step is to examine the filter itself and related structures.

filter surface. Check for breaks, tears, pinholes or tuck damage. Pay special attention to the joint between the filter material and the frame, the roots of the pleats and the corners of the outer frame. These locations are prone to damage during transportation or installation.

Netting and support structures. The function of the protective net is to protect the filter material, but if the protective net itself is loose, deformed, or made of improper material, fibers or particles may be produced. Check whether the protective net is damaged, whether it is firmly fixed, and whether the distance from the filter material is appropriate.

Edge sealing glue. If the colloid cracks, falls off or ages, it may produce particles. Check whether the glue seam is continuous and whether there is any abnormal peeling off.

Frame and seals. The surface treatment of the outer frame and the material and condition of the gasket may also produce particles. Especially after the gasket is aged, debris may fall off.

The installation process remains. Debris from installation, fragments of packaging materials, and particles from tool wear may all be found downstream. Check the installation records to confirm whether there are any leftovers that have not been cleaned up. involving HEPA/ULPA air filter products of different grades have the same inspection methods.

Downstream equipment may also be the source

Even if the filter element and installation are normal, fibers and particles may still be present downstream.

Equipment moving parts. Mechanical arms, transmission belts, guide rails, and cables may generate wear particles during operation. If these components are downstream of the filter, the particles generated can directly enter the protected area. Device-side applications should pay special attention to this.No matter how clean the air supply from the EFU equipment-side fan filter unit is, it cannot stop the continued wear of downstream mechanical parts.

Downstream piping and structural components. The coating on the inner wall of the air duct is peeling off, the flange sealing material is aging, and the valve is worn, which may produce particles.

Maintenance operations are introduced. When replacing the filter element, cleaning the equipment, or adjusting the structure, if the operation is improper, external particles may be brought downstream. Record the time and content of each maintenance operation and compare it with the time when the exception occurred.

The process produces dust. Some processes inherently produce fibers or particles. If the morphology of the abnormal particles matches the process material, the source may point to the process rather than the filter. For specific differentiation methods, please refer to the relevant instructions for troubleshooting substandard cleanliness.

How does evidence form a closed loop?

The process of locating the source requires a combination of on-site observation, sampling analysis and operating records.

Keep samples and photos. When an abnormality is found, the sample should be retained and photos should be taken to record the location and appearance. These are the basis for subsequent analysis.

Log operational changes. When did the exception occur? Has the filter been replaced, system adjusted, or equipment repaired before? Comparing these time nodes with the time when the exception occurred can help determine the source.

Compare historical data. If there was no similar anomaly before, what has changed recently? Air volume, pressure difference, operating mode, and maintenance operations may all be related.

Retest after correction. After processing or replacing relevant parts, retest under the same conditions. The rectification is completed only after confirming that the exception no longer occurs. You cannot just clean the surface and ignore the source, otherwise it may reoccur over time. Supporting FFU fan filter unit system, unit status and downstream environment should also be recorded together.

Project judgment example

After a piece of equipment has been running for a period of time, a small amount of fibrous particles are found at the downstream station.

Troubleshooting process: First confirm the sampling location and background to eliminate sampling contamination. Checking the surface of the filter element, it was found that there was a slight crease in a corner of the air outlet surface, but there was no obvious damage. Further inspection revealed that there was a cable tray near this location, which had slight contact with the surface of the filter element during installation. During operation, the equipment vibrates and the bridge frame rubs against the filter element, causing local fibers to fall off.

Treatment method: Adjust the position of the cable tray, replace the affected filter element, and clean the downstream pipelines. After processing and retesting, the exception no longer occurs.

This case shows that downstream fibers do not necessarily come from the filter element itself, and the installation structure may also be the source. involving ULPA ultra high efficiency filter or The method for troubleshooting HEPA high-efficiency filters is the same.

Selection and Acceptance Checklist

About Aili Industrial’s pollution traceability package

When fibers and particles appear downstream, the difficulty of investigation often lies in the multiple sources and dispersed evidence. If product information, installation records and operating data can be matched, positioning will be much faster.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For projects with downstream pollution, product structure data, installation drawings and on-site records can be combined to assist in checking possible sources and inspection points. When the filter is matched with equipment such as FFU and EFU, the interface design and material configuration can also be evaluated uniformly.

Providing abnormal sample information, installation records, and equipment structure during inquiry or troubleshooting can help narrow down the cause. The specific treatment plan is subject to on-site testing results and project acceptance conditions.