Should ULPA accept the air volume first or check for leaks first?

The order of these two actions is often reversed at the scene.

Let’s talk about the conclusion first: usually the air volume should be adjusted to the design working condition and run stably before on-site leak detection. If the order is reversed, with leaks detected first and air volume adjusted later, the previous leak detection data will most likely be invalid and need to be redone.

The reason is not complicated: leak detection readings are greatly affected by airflow conditions. If the air volume is not stable and the upstream concentration distribution is uneven, the scanning results will not be comparable. Neither 'qualified' nor 'unqualified' measured under such conditions can be used as the basis for final judgment.

Why stable air volume is the prerequisite for leak detection

On-site leak detection is generally carried out under operating conditions. When the probe scans the filter surface and interface, the change in readings is directly related to the air flow state.

If the air volume is unstable, the upstream concentration will be unstable. The aerosol generating device works normally, but fluctuations in air volume will change the concentration distribution. If the probe scans to the same position, it may read different values ​​at different times, making it impossible to determine whether it is a leak or a fluctuation in operating conditions.

If the air volume is incorrect, the leakage signal may be masked or amplified. When the air volume is low, some small leakage signals may not be obvious; when the air volume is high, local readings may be high, resulting in misjudgments. Only when the air volume is stable near the design conditions can the testing conditions correspond to the acceptance plan.

Changes in air volume will also affect the sealing state. After the system pressure distribution changes, the compression status of some interfaces may change. If you check for leaks first and then adjust the air volume, the sealing state may be different after adjusting the air volume than when you checked for leaks.

Therefore, the reasonable sequence is: the installation inspection is completed, the system is cleaned in place, the air volume is adjusted to the design value and operates stably, and then leak detection is started. Supporting FFU fan filter unit system needs to record the unit gear and operating mode; equipment-side applications such as For the EFU equipment-side fan filter unit , it is also necessary to confirm that the equipment itself is in stable working condition.

Recommended acceptance sequence

In actual operation, the acceptance can be broken down into several consecutive links:

Step one: Installation check. Check the filter element model, serial number, installation direction, and sealing structure. Check whether the installation frame is flat, whether the pressing parts are in place, and whether the filter element is fully seated.

Step 2: System cleaning confirmation. Whether the air duct and box have been cleaned. If there will be dust-generating construction such as grinding and welding in the future, it is recommended to postpone the leak detection, or to take protective measures and evaluate whether re-inspection is needed.

Step 3: Air volume debugging. Start the system, adjust the fan gear or damper, and adjust the air supply volume to the design working condition. Measure the surface wind speed or air volume to confirm that the distribution of each branch is reasonable. This link may require repeated adjustments until the system is stable.

Step 4: Stable operation. After the air volume is adjusted, let the system run for a period of time to confirm that the readings do not drift and the fan status is normal. For systems with large fluctuations in air volume, wait until it stabilizes before proceeding to the next step.

Step 5: On-site leak detection. Scan the filter material surface, edge sealing and installation interface according to the project plan. Record the test air volume, upstream concentration and scan path. If a leak is found, mark it first and then retest after processing.

Step 6: Regional particle testing. After passing the leak detection, measure the particle concentration in the protected area according to project requirements. This step does not have a one-to-one relationship with the filter grade, and is also affected by airflow organization and pollution sources.

This order is not fixed, but the logic is clear: first let the system enter a stable state, then verify the integrity, and finally confirm the spatial results. involving The acceptance method of HEPA/ULPA air filters is the same, and the criteria are implemented according to the corresponding standards.

Under what circumstances is retesting necessary?

After the air volume is adjusted, whether to re-check for leaks depends on the extent and method of the adjustment.

Situations that require retesting:

• The air volume adjustment range is large, and the system pressure distribution changes significantly.

• The fan gear or control parameters have been changed, and the operating status is different from before.

• The filter has been disassembled and installed, the compression parts have been adjusted, or the seals have been replaced.

• After leak detection, the leak was found and repaired or replaced.

• The system operating mode switches and the status corresponding to the design working conditions changes.

Situations that do not necessarily require retesting:

• Only minor corrections were made to the air volume, while the system pressure and sealing status remained basically unchanged.

• What is being adjusted is the branch air valve that has nothing to do with the filter interface, and it has been confirmed that this adjustment does not affect the pressure relationship before and after the filter.

• After the leak detection, no operations were performed to affect the sealing structure.

The judgment principle is: as long as the adjustment may change the air flow conditions or sealing status before and after the filter, the test should be retested. Record the time and content of each adjustment to facilitate subsequent traceability.

Special considerations for on-device applications

Device-side applications such as The EFU equipment-end fan filter unit has a compact internal space, and there are several additional points to note in the acceptance sequence.

There is little room for adjustment of air volume. The available height and fan capacity inside the equipment are limited, and the range of air volume adjustment may be narrower than at the end of the clean room. It is necessary to clearly confirm the air volume target during the planning stage to avoid repeated adjustments on site.

Leak detection routes must be planned in advance. There may be mechanical arms, cables or structural parts inside the equipment. Whether the probe can reach all the positions that need to be scanned must be confirmed during the planning stage. Locations that cannot be scanned should be stated in the record and cannot be qualified by default.

The operating status of the equipment must be stable. Equipment startup and shutdown, mode switching, or mechanical movement may affect local airflow. During leak detection and area testing, it is necessary to confirm that the equipment is in stable operation and record the working conditions at that time.

Project judgment example

During the ULPA acceptance of a certain piece of equipment, a leak test was first performed on-site and the result was satisfactory. Later, in order to adjust the air volume, the fan gear was raised from 60% to 80%. After running for a period of time, I retested and found that the reading on the border was too high.

The investigation found that after the air volume was increased, the system pressure distribution changed, and the sealing surface that was in the original compaction state was slightly bypassed under the new working condition.

If the air volume was adjusted first and then the leak was detected, the problem would have been discovered during the first leak detection, and there would be no need for secondary disassembly and re-testing. This case shows that the order is not just a process issue, it directly affects the validity of the test results.

In another project, after the air volume debugging was completed, the system ran stably for two days, and then leak detection and area testing were performed. All data passed once, and no abnormalities occurred in subsequent operations. The extra time spent in the early stage is saved in subsequent maintenance.

Selection and Acceptance Checklist

About Aili Industrial’s acceptance cooperation

The acceptance sequence seems to be an on-site operation arrangement, but if the products, fans and control parameters are correct in the planning stage, the on-site operation will be much smoother.

Aili Industry has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. When the filter is matched with equipment such as FFU and EFU, the air volume target, resistance data and interface conditions can be uniformly confirmed during the planning stage, which facilitates on-site leak detection and area testing under stable working conditions.

Provide design air volume, operating mode, installation conditions and acceptance requirements when enquiring, which will help confirm the appropriate configuration and testing plan. The specific acceptance methods and judgment standards are subject to the project plan.