How to prevent air leakage in spliced ​​ULPA modules?

For large-area filter arrays or special-sized air supply surfaces, ULPA often needs to be made into modules and spliced ​​on site. This solution is flexible, but the risk of air leakage is also more dispersed than that of a single filter element.

The core of module leakage prevention is not at the level of the single filter element, but at the joints, support, compression and installation sealing between modules. The single-piece filter element is factory-qualified. If the seams are not properly handled after splicing, air will bypass between the modules and the overall filtration effect will be compromised. Moreover, this kind of bypass is often not as obvious as the damage to the filter material, and it is easy to be ignored during troubleshooting. For specific leak detection boundaries, please refer to the relevant instructions for leak detection parts of FFU and EFU with ULPA.

First distinguish the connection level

There are more than one kind of joints in spliced ​​modules, and inspection and processing must be carried out in layers.

Internal splicing of modules. Some modules themselves are composed of multiple filter units with internal seams. These types of seams are usually processed during the manufacturing stage and cannot be adjusted on site.

between modules. This is the main seam that is spliced ​​on site. When modules are installed side by side, sealing is required between the frames of adjacent modules. The sealing method may be strips, gaskets, liquid tanks or special connectors.

Between the module and the box or mounting frame. The connection between the module group and the external box, ceiling or installation frame also falls within the scope of joints. If this layer is not properly sealed, air will also bypass it.

The significance of differentiating levels is that different handling methods lead to different responsible parties. The internal joints of the module are controlled by the manufacturer, the on-site joints are handled by the installer, and the box interface involves system design. involving For the splicing scheme of ULPA ultra-high efficiency filter , the seam design should be written into the technical documents.

Dimensional tolerance accumulation needs to be controlled

When multiple modules are spliced ​​together, dimensional deviations will accumulate.

Single module size deviation. Each module's outer frame has manufacturing tolerances. If the deviation of a single piece is close to the upper limit, after multiple pieces are spliced, the cumulative deviation may make the total size exceed the accommodation range of the installation frame.

Seams are uneven in width. Cumulative deviations can also result in inconsistent seam widths—wider in some locations and narrower in others. If the seal is designed to have a uniform width, it may not be compacted or over-compressed in joints with uneven widths.

The accumulation in the four corners is more obvious. At the corner position of module splicing, the deviations in the two directions are superimposed, and local gaps are prone to occur. Pay special attention to corners when checking.

Control methods. In the planning stage, the single module tolerance and cumulative tolerance range are clearly defined, and they are spliced ​​in order during installation to avoid concentrating the deviation on one side. If the cumulative deviation exceeds the range, the module size or installation sequence needs to be adjusted. For specific size measurement methods, please refer to the relevant instructions for high-efficiency filter size measurement.

Support and compression should be even

The effectiveness of seam sealing depends on the uniformity of the pressing force.

Frame deflection. When splicing long rows of modules, if the supporting structure is not rigid enough, the middle position may sink or bend. Frame deflection will cause joint widths to vary and the compression force to be distributed unevenly.

Pressure point arrangement. The compression piece should cover the entire length of the seam, not just the two ends. If there is a missing compression point in the middle, the seam may open.

Pressing sequence. Press it sequentially from one end to the other, or press it symmetrically from the middle to both sides to avoid the module being deflected due to force on one side first.

Support flatness. The installation surface should be flat and the bottom support of the module should be even. If the support is uneven, the module itself may tilt and the condition of the seams will be affected. At the equipment end or in large filter arrays, the accuracy of the support structure needs to be confirmed in advance. involving Modular solutions for HEPA/ULPA air filters , support and compression requirements should be incorporated into the installation plan.

Verify seams and intersections are covered

When detecting leaks in splicing modules, you cannot just scan the filter material surface.

Seam scan. Scan point by point along the seams between modules to confirm that the seal is continuous. The start, end and corners of the seams are important.

Interchange inspection. Where multiple modules meet, seams may cross. The sealing structures at these locations are more complex and are areas where leaks are prone to occur and need to be confirmed separately.

interface with the cabinet. The connection position between the module group, the cabinet and the installation frame must also be scanned. If this layer of interface is not properly sealed, air will bypass the periphery of the module group.

Inspection after replacing a single module. When replacing a module in a large-area array, in addition to inspecting the new module itself, it is also necessary to inspect the seams between it and adjacent modules. You can’t just scan the filter surface of the new module and end it. For specific leak detection methods, please refer to the relevant instructions for on-site leak detection.

Record unreachable locations. If some joints are obscured by structural members and cannot be scanned directly, this should be noted in the record. Cannot be qualified by default. Supporting FFU fan filter unit or For the modular air supply system of the EFU equipment end fan filter unit , joint accessibility should be confirmed during the planning stage.

Project judgment example

A large clean room uses spliced ​​ULPA modules to form the air supply surface. Leak detection after installation showed that the filter material surface of the single-chip module was normal, but the overall cleanliness test was slightly high.

After further scanning the module seams, it was found that there was a period of continuous abnormal readings in the seams between two rows of modules. The inspection found that the distance between the compression points at this location was too large and the seam in the middle was open. At the same time, the cumulative tolerance causes the joint width in this section to be slightly larger than other locations, resulting in insufficient compression of the gasket.

Treatment method: Add an intermediate compression point, adjust the installation sequence of adjacent modules, re-compact and then retest. Seams disappear abnormally. Mark this joint in the record as the focus of inspection for subsequent maintenance.

This case shows that air leakage from spliced ​​modules often comes from the seams and compression, rather than the filter material itself. involving HEPA high-efficiency filters has the same leakage prevention logic. The splicing scheme of

Selection and Acceptance Checklist