How to check the frame bypass after the chemical filter is installed?

After the chemical filter is installed, the frame bypass is an item that needs to be confirmed. Bypass means that part of the air does not pass through the filter material, but bypasses the gap between the filter element and the mounting frame. No matter how well the filter material is selected, the outlet concentration may not be able to decrease even if a bypass exists.

To check the frame bypass, it is recommended to proceed in two steps: first perform a structural inspection, and then perform a leakage inspection suitable for the system. Structural inspection covers gaskets, compression parts, frame contact surfaces and access doors; leakage inspection selects methods such as smoke, pressure or concentration comparison according to project conditions. Abnormal outlet concentration is not necessarily due to bypass, but bypass will allow untreated air to mix into the clean side, which needs to be eliminated first.

First look at the sealing and compression status

Structural inspection does not require sophisticated equipment, but it does require careful inspection.

Is the gasket continuous? Check the four sides and corners to see if the gasket is broken, displaced, detached or compressed unevenly. The sealing gasket of the chemical filter may be located on the air inlet side or the air outlet side. Check the product instructions for details. To confirm the position of the gasket, please refer to Discussion of whether the chemical filter gasket should face the inlet or outlet side .

Whether the pressing piece is in place. The number, location and tightening status of the hold-down parts should be checked. The four corners and the midpoint of the long side are places where it is easy to compact. Insufficient pressing force may cause the sealing gasket to fail to fit continuously. For specific performance, please refer to Discussion of the use problems that may occur if the chemical filter has insufficient pressing force .

Whether the frame contact surface is flat. Check whether the mounting frame is deformed, bulging solder joints, foreign matter or old seal remains. If the contact surface is uneven, there may be local gaps no matter how tight the pressing parts are.

Access doors and connections. The access doors, observation windows, pipeline interfaces, and joints of the splicing modules of the filter section should also be inspected together. Bypass does not necessarily only occur at the filter element frame, air leakage may also occur at these locations. For specific installation inspection, please refer to Discussion of what appearance and labels to check before installing a chemical filter .

Then choose a leak detection method suitable for your system

Leak inspection methods can be used when no problems are found during structural inspection, or when further confirmation is required.

Smoke check. Smoke is emitted upstream of the filter section, and observe whether there is smoke flow around the downstream border. The smoke-generating medium should be chosen to be of a type that does not pollute the filter material and does not affect subsequent processes. This method is suitable for quick judgment on site.

Pressure or air volume comparison. If there are pressure difference measuring points before and after the filter section, the pressure difference can be compared under stable air volume. However, normal pressure difference does not mean that there is no local bypass and can only be used as a reference.

Concentration comparison between upstream and downstream. Take samples at the inlet and outlet of the filter section to compare the target gas concentration. When the outlet concentration is high, it may be due to bypass, media consumption or inlet load changes. It needs to be judged together with structural inspection. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

Local concentration or wind speed scan. Measure the wind speed or target gas concentration at the edge of the air outlet surface, at the four corners, or near the access door. If a location has significantly abnormal readings, it may be a bypass path. For specific concentration pairing measurements, please refer to Discussion on whether the concentration before and after the chemical filter should be measured at the same time .

Contaminated tracers cannot be used. When chemical filters are used in clean or process environments, tracers must not contaminate the filter material or subsequent processes. The inspection method should be specified in the project plan.

Record leaks and locate them

After an exception is discovered, record it first and then handle it.

Mark the location. Mark clearly with a diagram or coordinates whether the leakage point is on which side, which corner, close to the gasket or access door. Multiple missing points are numbered separately.

Document inspection conditions. Air volume, operating gear, inspection methods, and environmental conditions must be recorded. During subsequent retests, the conditions should be as consistent as possible.

Distinguish between bypass and media failure. If the leakage points are concentrated on the frame, four corners or access door, bypass is more likely. If the overall concentration on the air outlet surface is high and there are no local abnormalities, it is more likely to be media consumption or inlet load changes. For detailed investigation, please refer to why the concentration at the outlet of the chemical filter is higher than that at the inlet . Discussion on

Do not change the filter material before positioning it. If bypass is the root cause, changing the filter material will not solve the problem. For specific life assessment, please refer to Discussion of how long chemical filters last .

Re-verify after correction

After locating the bypass position, correct it according to structural reasons.

Adjust the hold-down piece. If the pressing points are insufficient, add or adjust the pressing points; if the tightening sequence is unreasonable, tighten them gradually according to the design requirements. Do not tighten one corner first or over-tighten.

Replace or adjust gasket. If the gasket is displaced, broken or aged, replace it according to the product instructions. If the gasket is in the wrong position, reinstall it in the correct direction. Please refer to the specific directions to confirm Chemical filter airflow arrow unclear discussion on how to confirm.

Dealing with frameworks and interfaces. If the installation frame is deformed, the access door is poorly sealed, or the module joints are not tight, address the structural issues first. Adjust frame or replace seals if necessary.

Retest after correction. Recheck the frame bypass according to the same conditions to confirm that the leakage point is eliminated. If required by the project, retest the outlet concentration and air volume. involving FFU with chemical filter or The system, connections and maintenance methods of the MAU box-type chemical filter can be confirmed during the planning phase.

Project judgment example

After the chemical filter of a certain project was installed, the outlet concentration was higher than expected. Initial suspicion is that there is a problem with media selection.

During the investigation, we first conducted a structural inspection and found that the distance between the pressing points in the middle section of the long side on the right side of the filter element was too large, and the sealing gasket was under-compressed at this location. The smoke inspection confirmed that some air was bypassed here and did not pass through the filter material.

Treatment method: Add a compression point in the middle of the long side and re-tighten in sequence. The outlet concentration of the retest returned to the normal range, and the medium was not replaced. Mark this location in the record as the focus of subsequent maintenance inspections.

This case illustrates: Check the frame bypass after installation. You can start with tightening and sealing, and then use appropriate methods to confirm. involving When selecting a chemical filter product series , it is recommended to provide the installation sealing requirements and product information to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s installation and sealing packages

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide chemical filter product series and supporting air supply equipment. For projects that require on-site installation inspection, the installation frame structure, compression method and sealing requirements can be combined to assist in checking the filter element interface and inspection points.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . The specific technical documents and test results confirmed by the project shall prevail.