How to detect pinholes and holes in ULPA filter media?

Pinholes and holes are two forms of filter material damage, but their discovery methods and treatment judgments are different.

Pinholes are usually very small and may not be visible to the naked eye. It may be on the surface of the filter material or inside the pleats. The holes are more obvious and larger in scope, and can sometimes be judged from their appearance. In either case, visual inspection can only be used as a preliminary judgment and cannot replace integrity testing. Where the surface of the filter material appears to be intact, the actual penetration rate may have exceeded the limit due to changes in fiber structure or tiny pores.

Let us first clarify a principle: complete the test before touching the filter material with hands or tools. Pressing with fingers, stirring with tools, or blowing can expand the pinhole into a hole, or make the damage that could have been determined impossible to assess. For specific structural features, please refer to the relevant instructions for the structure without partitions.

What can be found by visual inspection?

Visual inspection is the first step in detection, but it is not the final basis.

What can be found: obvious tears, holes, fold breaks, foreign matter indentations on the surface of the filter material, and damage to the protective net. These injuries are usually extensive and can be judged by their appearance.

What is not easy to find: tiny pinholes, local damage inside folds, areas with changes in fiber structure but intact surfaces. These require detection methods to identify.

Check method. In a well-lit environment, observe the surface of the filter material from different angles. You can use a magnifying glass to assist in inspecting edges and glue seams. Be careful not to touch the filter material directly with your hands, and do not blow or slap on the filter material. involving The inspection of ULPA ultra-high efficiency filter can be checked with the product information of the corresponding model.

If obvious holes are found through visual inspection, the location and range should be noted in the record, and then leak detection and confirmation should be carried out according to project requirements. The location of the hole and the surrounding area are the focus of scanning.

How to locate pinholes in integrity testing

Pinholes and tiny local damage are mainly located by scanning and leak detection.

Scan method. According to the testing standards and plans adopted by the project, use the specified aerosol, instrument and scanning parameters to scan point by point along the filter surface. The reading characteristic of a pinhole is usually a local peak with a small range, and the reading returns to normal after leaving this position.

Positioning requirements. After an abnormality is discovered, mark the location coordinates to confirm whether the signal reappears. The difference between a single reading fluctuation and a stable leak is repeatability. If there are abnormalities in multiple scans at the same location, it can be initially determined that there is a leak. For specific scanning methods, please refer to the relevant instructions for leak detection at the interface between the filter material and the frame.

The difference from glue seam leakage points. The pinhole is on the surface of the filter material, and the glue seam leakage point is at the junction of the filter material and the frame. Combine position and structure judgment when positioning. If it is abnormally close to the glue seam, check the glue seam first; if it is in the middle of the filter material, suspect damage to the filter material first. For specific positioning methods, please refer to the relevant instructions for leak positioning.

Detection capabilities must match. The local judgment limits of ULPA are stricter than HEPA, and the instrument's range, sensitivity and background control must meet the requirements. Zero counts do not equate to absolutely no penetration and may be lower than the detection capability of current methods. For specific differences, please refer to the relevant instructions for leak detection requirements.

Hole processing boundaries

The treatment of holes depends on the scope, location and project acceptance requirements.

Small damage. Some projects allow the repair of local defects in the filter material within a limited range, but the repair materials, methods and re-inspection requirements need to be carried out in accordance with the model description and project documents. Doing it yourself without permission is not recommended.

Extensive holes. If the range exceeds the allowable repair limit, or involves multiple pleats or edges, the filter element usually needs to be replaced. Forcible repair may affect filtration efficiency and structural stability.

Accompanied by structural damage. If the hole is accompanied by deformation of the outer frame, cracking of the glue seam, or damage to the protective net, it means that the degree of damage has exceeded the filter material itself. In this case, even if the filter media is repaired, there may be issues with the sealing and structural integrity of the entire product. For specific inspection methods, please refer to the relevant instructions on frame deformation.

Location sensitive situation. If the hole is located at the edge of the filter material, near a glue seam, or near the installation sealing surface, the treatment requirements may be more stringent. These locations not only affect filtration but may also affect sealing.

After the treatment is completed, re-test according to the same working conditions, covering the repaired location and surrounding areas. Keep inspection records and location information before and after treatment. involving HEPA/ULPA air filter has the same logic. The processing judgment of

How to avoid damage during installation and use

The source of pinholes and holes is often during installation or operation.

Support the outer frame when transporting. Do not press the surface of the filter material or the protective screen. Device-side applications such as The EFU equipment-side fan filter unit has a compact internal space, making it easier to touch the filter media during transportation and assembly.

Protect the filter surface during installation. If tools, screws or structural parts are close to the filter material, avoid collision during operation. After confirming the installation direction, install it in the correct direction and do not force it in. To determine the specific direction, please refer to the instructions related to the inlet and outlet wind direction.

Avoid foreign matter entering during operation. If foreign objects fall off upstream, they may hit the filter material and cause damage. Pre-filtration and protection measures must be taken. For specific configuration, please refer to the instructions related to pre-filtering.

Do not purge the filter material during maintenance. Purging with compressed air may enlarge the pinholes or press particles into the filter material. If there is dust on the surface of the filter material, follow the product instructions and do not blow it away by yourself. For specific maintenance requirements, please refer to the instructions related to cleaning and purging.

Monitor data during operation. Supporting In the FFU fan filter unit system, if the pressure difference suddenly drops or the air volume changes abnormally, it may indicate damage to the filter material. Judge together with the leak detection results.

Project judgment example

During an on-site leak detection on a certain project, a ULPA found a stable abnormal reading in the middle of the filter material surface. Visual inspection revealed no obvious damage.

Upon further observation with a magnifying glass, there is a very small dark spot at this location, which may be a pinhole or fiber damage. After recording the location, evaluate the treatment as required by the project. Since this location is in the middle of the filter material and the scope is very small, the project allows repair according to regulations. After repairing and retesting, the abnormality disappeared.

In another product, a large hole was found on the edge of the filter material, covering two pleats, and there was slight deformation at the corners of the outer frame. This situation was beyond the scope of repair and it was decided to replace the filter element. After replacement, check the installation frame and compression structure to confirm that there are no abnormalities.

This case illustrates: The treatment of pinholes and holes must be based on the judgment of location, scope and structural status. Not all damage can be repaired, and not all abnormalities require replacement.

Selection and Acceptance Checklist

About Aili Industrial’s filter material damage detection package

The difficulty in detecting pinholes and holes lies in 'how to judge areas that are invisible to the naked eye.' This requires the coordination of product structure data, testing methods and on-site records.

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 integrity of the filter material and the quality of the glue seams are included in the testing scope. For projects with filter material damage, product structure information and on-site photos can be combined to help determine the type of damage and inspection points. When the filter is matched with equipment such as FFU and EFU, the installation space and disassembly path can also be checked together during the planning stage to reduce damage to the filter material caused by structural interference during operation.

Provide damage information, installation records and inspection data during inquiry or inspection to help confirm the appropriate treatment direction. The specific handling method shall be subject to on-site inspection results and project acceptance conditions.