How to detect leaks at the junction of ULPA filter material and frame?

The junction between the filter material and the frame is a section that is easily skipped in ULPA leak detection.

When scanning the filter surface, the probe moves from the center to the edge, and often slows down or stops when it gets close to the frame - because the probe may hit the frame, or the scanning angle is limited. In order not to affect the progress, some operators will skip this section and go directly to the next one. But this location is precisely the high-risk area for leaks.

The filter material and frame are connected by edge sealing glue. If there are discontinuities, bubbles, partially uncured parts, or interface peeling in the glue seam, air may bypass the edge of the filter material. This kind of leakage point is not as obvious as the pinhole in the center of the filter material. The signal may be continuously high along the edge rather than a sharp peak. For specific glue joint failure modes, please refer to the relevant instructions on glue joint cracking.

Define the boundaries clearly first

Before detecting leaks, first clearly define the range of 'junction between filter material and frame'.

Filter media edge. The end of the pleated filter material is usually embedded in colloid or attached to the frame. When scanning, it is necessary to cover the root of the pleats, not just the flat part of the filter material.

Glue seam interface. There may be leakage points at the bonding surface between the colloid and the filter material, and between the colloid and the outer frame. During inspection, the position and width of the glue seam need to be confirmed, and the scanning path must cover these two interfaces.

Border corners. The four corners are where discontinuities in glue seams tend to occur. Pleats are treated differently at corners than straight edges, and the gel may flow and solidify differently at corners.

sealing surface. The sealing surface of the frame and the installation frame belongs to another detection range, but when detecting leaks on the filter element body, if the sealing surface has been installed in place, the scanning range may also extend to this position. Boundary demarcation should be clear in the project plan to avoid duplication or omission. For specific sealing methods, please refer to the relevant instructions for liquid tank sealing.

How to move the probe

The scanning path at the junction of the filter material and the frame is different from the center of the filter surface. There are a few points to pay attention to during operation.

The probe distance should be stable. When approaching the frame, the probe may change distance due to structural obstruction. As the distance increases, the sensitivity decreases; if the distance is too close, it may hit the glue seam and cause damage. The operating space at this location should be considered when planning the path.

The scanning speed needs to be controlled. The leakage signal at the edge and glue seam position may be continuous, and the probe may move too fast and there may be no time to respond. The speed must be controlled according to the method requirements and cannot be accelerated just because it is close to the border.

Coverage should overlap. When sweeping from the filter surface to the edge, there must be a certain overlap between the paths to avoid unscanned gaps at the intersection.

The four corners should be treated separately. After the straight edge scan is completed, the four corners need to be confirmed individually. The rotation and positioning of the probe at the corners may be limited. Adjust the scanning angle or use auxiliary tools if necessary. If certain locations are truly unscannable, this should be clearly marked in the record and should not be deemed qualified by default. involving For on-site leak detection of ULPA ultra-high efficiency filters , the recording requirements are the same.

How to deal with structural occlusion

In equipment-side applications and certain installation forms, the interface between the filter material and the frame may be blocked by structural components.

Netting and supports. If the protective net covers the glue seam, the probe may not be able to make direct contact. It is necessary to confirm the distance between the protective net and the glue seam, and whether the probe can approach the opening of the protective net.

Diffuser plates and guide structures. High-efficiency air supply vents or If there is a diffuser plate inside the FFU fan filter unit , it may block the frame area after installation. The timing and sequence of leak detection should be confirmed at the planning stage - whether to remove the diffuser plate and check again, or verify through other methods.

Internal structure of the device. Device-side applications such as The EFU equipment-side fan filter unit has a compact internal space, and the robotic arm, cables or transmission parts may block part of the frame. Evaluate scanning accessibility before installation, and adjust the installation sequence or design detection channels if necessary. For the specific installation sequence, please refer to the instructions on whether to adjust the air volume first or detect leaks first.

How to handle occlusion positions. If some interfaces are indeed unscannable, alternative verification methods should be agreed upon in the acceptance plan, or recorded as unreachable areas. Just because it is not scanned does not mean that the seal is qualified by default.

How to deal with leaks found

When an abnormality in the junction position is detected during scanning, locate it first and then determine the type.

Distinguish between glue joint problems and installation problems. Cracked glue seams and discontinuous colloids are problems with the filter element itself; air leakage between the frame and the installation frame is a problem with the installation interface. The two are handled differently. When positioning, the leakage point coordinates and structural position are combined to determine.

Record the distribution of leak points. Is it a single point, continuous along an edge, or all four corners? Distribution characteristics can help determine the cause. A single point may be a local defect, continuity along the edge may be an overall problem with the glue joint, and the appearance of four corners at the same time may be related to frame deformation or installation and compression methods.

The processing method is based on project requirements. Whether the leakage point at the junction of the filter material and the frame can be repaired, the repair scope and re-inspection requirements shall be carried out according to the model description and project acceptance conditions. It is not recommended to continue using the product after refilling it without permission. For specific repair boundaries, please refer to the instructions related to glue seam cracking.

Retest after correction. After the processing is completed, the location and surrounding area are rescanned under the same conditions. Confirm that leaks are eliminated and keep records before and after treatment. involving HEPA/ULPA air filters are the same. The requirements for leak detection and retesting of

Project judgment example

During on-site leak detection in a certain project, the center scan of the filter surface was normal, but there was a period of continuous abnormal readings on the right border of one filter element.

Further positioning revealed that the anomalies were concentrated at the glue seam, with a range of approximately 150 mm. Inspecting the appearance, no obvious cracks can be seen on the surface of the glue joint, but when observed with a magnifying glass, slight discontinuities can be seen locally. After removing the filter element, confirm from the back that there are bubbles in the colloid at this location.

Treatment method: The glue joint in this section exceeds the allowable repair range, and the filter element must be replaced. After the new filter element is installed, focus on scanning the junction position to confirm that the glue seam is continuous. This location is noted in the record as a key area for subsequent leak detection.

The key point in this case is: passing the center of the filter surface does not mean passing the entire filter surface, and the junction positions must be covered separately. involving ULPA ultra high efficiency filter or The acceptance of HEPA high-efficiency filters has the same judgment logic.

Selection and Acceptance Checklist

About Aili Industrial’s junction leak detection package

Whether leak detection can be done at the junction of the filter material and the frame is related to the structural design of the filter element and the accessibility of the probe. If the product takes scan paths into consideration during the design phase, on-site operations will be much smoother.

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. During the filter manufacturing process, the quality of the glue seams and edge sealing are included in the inspection scope. For on-site leak detection projects, the product structure, installation method and project leak detection plan can be combined to help confirm the scanning path and recording requirements. When the filter is matched with equipment such as FFU and EFU, the impact of the installation sequence and blocking position can also be evaluated together during the planning stage.

Specifying leak detection requirements, installation conditions and acceptance methods when enquiring, will help confirm the appropriate structure and recording scheme. The specific testing methods and judgment standards are subject to the project plan.