Why might the system still leak air even if the filter body is qualified?

The filter element that arrived had a factory inspection report and the efficiency level also met the requirements. After installation, the on-site leak test failed. This situation is not uncommon in projects.

The reason is not complicated: the factory report proves the performance of the filter element body under specified test conditions, and the installed system includes the filter element, frame, sealing gasket, box seams and access openings. Air may bypass the filter media from any of these connections. There is nothing wrong with the filter element itself, the leak is somewhere else.

The air leakage path is more than just the filter material

During on-site inspections, there are more places to check than you think.

Filter material surface : damage to the filter paper itself, pinholes, or damage to the pleats.

The junction between the filter material and the frame : whether the glue line is continuous and whether the colloid is firmly bonded to the filter material and frame.

The sealing surface of the frame and the mounting frame : the pressing state of the gasket and the matching state of the liquid tank and the knife edge are all on this layer.

Box connections : box joints, flange connection surfaces, and access doors.

Pipes and other openings : If there are other openings or connections in the system, they may also become bypasses.

If you only scan the surface of the filter material during on-site leak detection, you may miss the real problem location. The complete scanning path should cover the entire air supply path from the filter material to the box. Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space and poor interface accessibility. It is necessary to plan the scan path in advance during troubleshooting.

Factory inspection and on-site leak detection solve different problems

These two tests are often conflated and have different practical effects.

Factory testing verifies the performance of the product under specified conditions, and the test object is the filter element body or the complete product. On-site leak detection verifies the actual sealing state after installation, and the test object is the combination of the filter element and the installation structure.

The two are not substitutes for each other. If the product is qualified, it does not mean that the installation is qualified; if the on-site leak test is passed, it does not mean that the factory test is OK. Both materials have their own purposes during project acceptance, and it is recommended to file them separately. involving For products of different grades of HEPA/ULPA air filters , the testing requirements and judgment standards may be different. The verification shall be carried out according to the corresponding documents.

Just replacing the filter element cannot solve the frame problem

When a leak is discovered on site, many people’s first reaction is to replace the filter element. But if the leakage point is in the frame or box, it won’t matter how many times you replace the filter element.

Common frame problems include: uneven sealing surface caused by deformation of the installation frame, loose or uneven distribution of pressing parts, aging and loss of rebound of the gasket, bent edge of the liquid tank or bulging seams. These issues require dealing with the structure first and then considering the filter element.

Specific to the sealing structure of the liquid tank, the matching state of the knife edge and the tank body is the focus of the investigation. For the verification method, please refer to the relevant interface instructions. in the case of For the box supporting the FFU fan filter unit , it is also necessary to confirm whether the box itself has any joints or openings that are not closed.

Reasonable order of investigation

After discovering air leakage, it is recommended to proceed in this order:

First confirm the location of the leakage point and mark it on the filter element number and location diagram. Then determine which category the leakage point belongs to - filter material, edge sealing, sealing surface or box. Then deal with it in a targeted manner: for filter material problems, consider replacing the filter element, for sealing surface problems, check the pressing structure and gasket status, and for box problems, structural defects need to be dealt with.

After the treatment is completed, re-inspect according to the project plan and record the results before and after treatment. Repairing the filter paper without positioning it or replacing the filter element repeatedly will prolong the problem. For the location after the sealing material is replaced or the structure is adjusted, the leakage should be re-tested according to the conditions agreed on the project, and the original acceptance conclusion should not be used.

About Aili Industrial’s leak detection cooperation

Aili Industrial produces HEPA/ULPA filters and supporting FFU fan filter unit、EFU equipment-side fan filter unit and high-efficiency air supply outlet. The filter and air supply equipment are matched in the same manufacturing system, and the sealing structure and interface size can be checked uniformly before leaving the factory to reduce leakage points caused by mismatched interfaces on site.

For items that fail on-site leak detection, the filter element number, installation location and leak point record can be provided to facilitate the determination of whether the problem lies on the product side or the installation side. The specific testing methods and judgment standards are subject to the project plan.