How to arrange the aerosol upstream of ULPA leak detection?

During on-site leak detection, the scan readings were abnormal, and many people's first reaction was that there was a problem with the filter element. But there is one situation that is often overlooked: the upstream aerosol itself is not arranged properly, and the downstream readings will also be distorted.

The aerosol concentration is low, and the leak signal may not be obvious; the concentration is uneven, and the reference readings at different locations are different, and the scanning results cannot be compared horizontally; the concentration fluctuates greatly, and the readings of multiple scans at the same location are inconsistent, and it is impossible to determine whether it is a leak or a change in conditions. The upstream layout was not in place, and subsequent scans were based on unstable judgments. To confirm the specific leak detection conditions, please refer to the instructions related to unstable air volume during leak detection.

First determine the concentration according to method requirements

The aerosol concentration is not set at random, nor is the higher the better.

Determine according to the detection method and instrument range. Different detection methods and different instruments have different requirements for upstream concentration. The local judgment limit of ULPA is stricter than that of HEPA, and the instrument needs to have a suitable upstream concentration to distinguish signals near the target limit. If the concentration is too high, it may exceed the instrument's range; if the concentration is too low, it may fall below the detection capability. For specific differences, please refer to the relevant instructions for HEPA and ULPA leak detection requirements.

Different specifications cannot mix concentration requirements. EN 1822 and ISO 29463 have their own regulations on the generation and measurement of aerosols. During on-site testing, it should be carried out according to the standards and plans adopted by the project, and the concentration under one standard cannot be directly applied to another standard.

The aerosol type should match the filter material. Different filter materials have different suitability for aerosols. Especially for PTFE membrane materials, certain aerosols or test conditions may have an impact on the material. Before testing, you should confirm with the supplier the aerosol type that the product is suitable for, and do not replace it yourself. involving The leak detection method of ULPA ultra-high efficiency filter should be confirmed according to the corresponding product information.

Injection point and mixing distance

The location of aerosol injection and the length of the mixing section directly affect the uniformity of the upstream concentration.

Injection point location. The aerosol should be injected into the upstream side of the filter, usually after the fan, in the pipe section before the filter, or in the plenum. The injection point should avoid local high-speed areas, elbows and valves. The air flow in these locations is unstable and the mixing effect is poor.

Mixed distance. There needs to be enough straight pipe section or mixing space from the injection point to the windward side of the filter to allow the aerosol and air to be fully mixed. If the mixing distance is insufficient, the local concentration may be too high or too low. If the system space is limited, you can consider adding a mixing device, but you need to confirm that it will not add additional resistance. Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space and the mixing section may be short, so special evaluation is required during layout.

The impact of obstacles. Obstacles, diameter reduction, and guide plates in the pipe section may affect the mixing uniformity. Try to avoid these locations when laying out, or verify that the impact is within the acceptable range.

When multiple filters share upstream. If multiple filter elements share an upstream mixing section, the concentration on the windward side of each filter should be confirmed separately and cannot be completely consistent by default. Supporting FFU fan filter unit system, the air volume distribution between units will also affect the concentration distribution.

Uniformity and stability need to be verified

After the layout is completed, it cannot be assumed that the concentration has been uniform and stable, and actual verification is required.

Uniformity verification. Divide measuring points into equal areas on the windward side of the filter and measure the aerosol concentration at each point. If the readings at each point have a large deviation, it means that the mixing is insufficient and the injection point position needs to be adjusted or the mixing distance needs to be increased. For specific measurement point layout methods, please refer to the relevant instructions for surface wind speed calculation.

Stability verification. Continuously monitor the concentration within a specified period of time to confirm that there is no significant drift or fluctuation. If concentration fluctuations exceed the allowable range of the method, the comparability of scan results will be affected. When the fluctuations are large, the influence of the aerosol generating device, pipeline connections and ambient air flow should be investigated.

Sampling point settings. The upstream sampling point should be set at a location that represents the average concentration on the windward side of the filter, avoiding local high-speed areas or low-speed retention areas. The sampling tube must be sealed and unobstructed to avoid clogging or water accumulation.

Monitor continuously during the scan. During leak detection, upstream concentrations may change due to aerosol consumption, temperature changes, or system disturbances. It is recommended to keep monitoring during the scanning period and record concentration changes if necessary as a reference for result interpretation. For specific recording requirements, please refer to the relevant instructions for leak detection report records.

Layout conditions and records

The layout parameters and verification results of upstream aerosols should be included in the detection records.

Record content. Aerosol type, injection point location, mixing section length, upstream concentration value, uniformity verification results and stability monitoring data.

Corresponds to the filter element number. The testing conditions of each unit or each area should be associated with the corresponding product number and installation location. During subsequent retests or troubleshooting, the same conditions can be restored.

Exception handling. If an abnormal concentration is found during scanning, the detection should be suspended and the cause should be investigated before restarting. Do not continue scanning under unstable concentration conditions, as the data obtained cannot be used as a basis for judgment.

Cooperate with other conditions for on-site leak detection. Aerosol layout is only part of the leak detection conditions. Stable air volume, background control and probe distance are equally important. For specific control methods, please refer to the instructions related to the scanning probe distance. involving For on-site leak detection of HEPA/ULPA air filters , the condition confirmation method is the same.

Project judgment example

During an on-site leak inspection on a certain project, it was found that the benchmark readings of the same ULPA at different locations were quite different. When scanning the filter surface, some areas have higher readings and some have lower readings.

The investigation found that the aerosol injection point was too close to the windward side of the filter and the mixing was insufficient. The upstream concentration is unevenly distributed on the windward side, causing the scan datum itself to be biased.

Treatment method: Adjust the position of the injection point, increase the mixing distance, and re-verify the concentration uniformity at each point on the windward side. After confirming that the uniformity meets the requirements, scan again. After adjustment, the reference readings tend to be consistent and leakage signals are easier to identify.

This case illustrates that improper arrangement of upstream aerosols will affect the reliability of the entire leak detection results. involving HEPA high-efficiency filters are the same. The leak detection and layout principles of

Selection and Acceptance Checklist

Regarding the leak detection conditions of Aili Industry

The upstream aerosol arrangement essentially provides a stable and comparable testing condition for leak detection. If this condition is planned during the planning stage, the on-site inspection 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. For projects that require on-site leak detection, the system structure, installation method and detection plan can be combined to help confirm the aerosol injection location, mixing section conditions and sampling point layout. When the filter is matched with equipment such as FFU and EFU, the upstream space and interface conditions can also be evaluated together during the planning stage.

Explaining the leak detection method, system structure and acceptance requirements when enquiring, will help confirm suitable testing conditions. The specific testing methods and judgment standards are subject to the project plan.