Is it normal for the pressure difference to suddenly become low while the chemical filter is running?

Direct answer: It may not be normal, and the cause needs to be investigated.

When the pressure difference becomes lower, some people will think that 'the resistance is small, which means the filter material is still clean, which is a good thing.' However, a sudden drop in the pressure difference of the chemical filter often indicates that a change has occurred in some link in the system. It may be that the air volume has decreased, the measurement is abnormal, the installation is loose, or there may be a problem with the filter material structure. If ignored directly, it may cause the outlet concentration to exceed the standard or the system operation to be unstable.

First confirm the system air volume

The pressure difference is directly related to the air volume. When the air volume decreases, the pressure difference will naturally decrease.

Fan status. Check whether the fan speed has slowed down, stopped or malfunctioned. If a certain unit in the group control system is running at reduced speed, you may not be able to detect it just by looking at the panel. For detailed investigation, please refer to Discussion of what to check if the pressure difference before and after the chemical filter suddenly rises .

Air damper and valve opening. If there is a damper in the system, changes in opening will affect the air volume passing through the filter section. If the valve is misadjusted, stuck, or has abnormal automatic adjustment, the air volume may decrease.

Switch operating mode. Switching the equipment from production mode to standby mode, adjusting the fresh air ratio, and starting and stopping other branches will all affect the air volume passing through the chemical filtration section. Record the current operating status and determine whether the pressure difference changes are synchronized with the changes in operating conditions.

Actual air volume measurement. If conditions permit, measure the actual air volume passing through the filter section. The air volume decreases and the pressure difference decreases simultaneously, indicating that the change comes from the system rather than the filter material itself.

Check bypass and location

There is no significant change in air volume, but the pressure difference decreases. Check the filter section itself.

The filter element is displaced or loose. Vibration during equipment operation may cause the filter element to slowly deviate from the installation position. When a gap appears between the filter element and the installation frame, part of the air bypasses the filter material, reducing the actual air volume passing through the filter material and reducing the pressure difference.

The gasket is detached. A bypass path may also be formed if the sealing gasket is displaced, broken or aged. After bypass, the pressure difference decreases, but the outlet concentration may increase. For specific inspection methods, please refer to Discussion on how to check frame bypass after chemical filter installation .

The access door or interface is loose. If the access door, observation window, and pipeline interface of the filter section are not properly sealed, bypasses will also be formed. These locations need to be checked along with the filter element seal.

The hold-down piece is loose. If the compression piece becomes loose due to vibration, the sealing gasket may not be able to maintain a compressed state, forming a local bypass. For specific impacts, please refer to Discussion of the use problems that may occur if the chemical filter has insufficient pressing force .

Distinguish measurement faults from real changes

The differential pressure reading itself can also be problematic.

Zero point of differential pressure gauge. The meter may drift after long-term operation. When the reading is low, first confirm the zero point status of the instrument.

Pressure pipe. If the pressure guide tube falls off, leaks, is clogged or bent, the reading will deviate from the actual value. Check whether the high and low pressure side pipeline connections are normal.

sensor signal. For differential pressure sensors with signal output, it is necessary to confirm whether the signal transmission and display are normal. If a certain unit in the group control system communicates abnormally, the panel reading may not reflect the actual status.

Compare with other measuring points. If the pressure difference of other filter sections in the same system is normal and only this section is abnormal, the scope of investigation can be narrowed down.

Media structure may vary

After eliminating system, installation and measurement factors, consider the filter media itself.

The filter material shrinks or settles. Some filled or composite media may shrink or settle due to vibration, air flow or changes in temperature and humidity during operation, resulting in enlarged channels and reduced pressure difference. This condition is often accompanied by a decrease in processing power.

The media is powdery or damaged. If the medium is pulverized, broken or structurally damaged, the air flow may be short-circuited and the pressure difference may be reduced. Such changes require unpacking and inspection for confirmation.

Dry after getting wet. If the pressure difference increased due to moisture before, then the water evaporates and the medium dries, the pressure difference may fall back. However, this does not mean that the condition of the filter material has been completely restored and needs to be evaluated according to the product instructions. For specific environmental impacts, please refer to Discussion of how long chemical filters last .

Verify outlet concentration after structural changes. Changes in the medium state may affect the treatment effect, and you cannot continue to use it just to see the pressure difference recover. For specific methods, please refer to Discussion of sampling points for chemical filter performance verification .

processing and review

After confirming the cause, handle it accordingly.

Air volume problem. Restore the status of the fan or damper, and re-measure the pressure difference and air volume.

Bypass problem. Adjust the pressing parts, replace the sealing gasket or repair the interface according to the structural requirements. After correction, check the frame bypass and re-measure the pressure difference and outlet concentration. For specific methods, please refer to Discussion on how to check frame bypass after chemical filter installation .

Measurement issues. Calibrate or replace the instrument, repair the pressure pipe, and retest the reading.

Filter material problem. If it is confirmed that the media shrinks, pulverizes, or is structurally damaged, evaluate whether to replace it according to the product description and project requirements. Re-establish pressure differential and outlet concentration baseline after replacement.

Review content. After treatment, it is recommended to re-measure the air volume, pressure difference and outlet concentration at the same time. Only by looking at the three together can we judge whether the system is truly back to normal. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

Project judgment example

The pressure difference of the chemical filter in a certain project suddenly dropped, and the site believed that 'lower resistance is a good thing.'

During the investigation, we first checked the air volume and found that the fan gear did not change, but the actual air volume dropped. Checking the filter section, it was found that the sealing gasket on one side of the filter element was detached and some air passed through the bypass path. The actual processing air volume of the filter material decreases and the pressure difference decreases, but the outlet concentration increases.

Treatment method: Replace the sealing gasket, re-tighten it, and re-measure the pressure difference and outlet concentration. After adjustment, the pressure difference recovered and the outlet concentration returned to the normal range.

In another project, after the pressure difference decreased, it was found that the pressure pipe joint was loose and the pressure difference gauge read low. After reconnecting the pipeline, the reading returned to normal and there was no problem with the filter material itself.

These two cases illustrate: if the pressure difference suddenly becomes low, check the air volume, bypass and measurement first, and then evaluate the condition of the filter material. involving When selecting chemical filter product series , it is recommended to provide pressure difference records, air volume data and installation conditions to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s pressure difference investigation and supporting services

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 with abnormal pressure differences, pressure difference records, air volume data, installation status and operating conditions can be combined to assist in checking the investigation direction and treatment plan. When the filter is matched with MAU, FFU, EFU and other equipment, the location and maintenance method of the sampling port can be confirmed uniformly.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . Providing differential pressure records, system conditions and operating data when enquiring, to help confirm a suitable solution. The specific selection is subject to the technical documents and test results confirmed by the project.