What should I check if the pressure difference before and after the chemical filter suddenly rises?

When the pressure difference of a chemical filter suddenly increases, the first reaction is often 'the filter material is blocked and it is time to change it.' This judgment may be correct, but it may also lead to a biased direction.

The pressure differential reflects air flow resistance, not gas handling capacity. The increase in pressure difference may be caused by dust accumulation on the filter material, hardening due to moisture, filling displacement, blockage of the pre-filter, increased air volume, abnormal measurement pipeline, or even changes in the system valve. Treatments vary. Directly replacing the filter material sometimes cannot solve the fundamental problem.

The order of troubleshooting is recommended to start with measurement and working conditions, then check the filtration path, and finally judge the gas treatment effect.

Check the measurement and working conditions first

If the differential pressure gauge reading rises, first confirm whether the reading itself is reliable.

Differential pressure gauge status. Check zero point, span and calibration status. The meter may drift after long-term operation, and the reading may not necessarily reflect the actual pressure difference.

Pressure pipe. Check whether the pressure port is blocked, whether the pressure guide tube is bent or water accumulated, and whether the high and low pressure sides are connected correctly. Abnormalities in the pipeline will cause the reading to deviate from the actual value.

Actual air volume. Record the current air volume and fan gear. When the air volume increases, the pressure difference will naturally increase. If the fan gear or damper has been adjusted recently, the change in differential pressure may simply be the result of changes in operating conditions. For the specific relationship between air volume and pressure difference, please refer to Discussion on whether the chemical filter air volume should be selected based on the total air volume of the system or the air volume of a single unit .

operating mode. Starting and stopping equipment, switching production modes, and adjusting the proportion of fresh air will all affect the air volume passing through the filter section. Record the working conditions at that time to avoid misjudgment of changes in working conditions as filter material clogging.

Check pre-filtration and particle load

After the measurement and working conditions are confirmed to be normal, check the front end first.

Pre-filter status. Are the primary and medium-efficiency filters seriously dusty, damaged, or have bypasses installed? If the front end fails, dust will directly enter the chemical filter section, causing the pressure difference to increase. Many problems with increased pressure difference are rooted in pre-filtration.

Particle load changes. Has there been any recent construction, repairs or process adjustments that have resulted in additional dust? If so, address the source of the particles first and then evaluate the status of the chemical filtration section.

Surface dust treatment. If there is only dust on the surface of the filter material, it is not recommended to wash or blow it directly. Check the pre-filter first, and then handle it according to maintenance requirements. For specific methods, please refer to Discussion on how to deal with dust falling on the surface of chemical filters .

Check for moisture, condensation and droplets

Moisture is one of the common causes of abnormal pressure differentials in chemical filters.

Operating temperature and humidity. Check the temperature and humidity records before and after the filtration section. High-humidity environments may cause some media to absorb moisture, solidify, or expand, increasing airflow resistance.

Risk of condensation. Is there condensation or droplet entrainment after the surface cooler, behind the humidification section, or near the cold surface? After liquid droplets enter the filter material, the media may agglomerate and the pressure difference rises. Please refer to the specific layout Discussion on how the chemical filter of the air conditioning box should be arranged before and after the humidification section .

Drainage and retain water. Check whether the drainage is smooth and whether the water baffle is effective. Chemical filters cannot replace water removal structures. If the system itself presents a risk of droplets, the source of the moisture should be addressed first.

Judgment after getting wet. The dry appearance of the filter element does not mean that the internal condition is normal. After getting wet, you should evaluate whether to continue using it according to the product description and project requirements. For specific life span judgment, please refer to Discussion of how long chemical filters last .

Check the condition of filter media and structure

After eliminating the front-end and moisture factors, check the chemical filter section itself.

Media status. Check whether the filter material is hardened, pulverized, unevenly filled, or shrinks significantly. Some media may change their structure after absorbing moisture or reacting, resulting in increased resistance.

Padding and support. The media of a packed filter may shift, causing local channel blockage. Loose support structures may also cause changes in media distribution.

Frame and seal. Is the outer frame deformed? Has the gasket shifted or become dislodged? Please refer to the frame bypass inspection method after installation. Discussion on how to check frame bypass after chemical filter installation .

Filter segment structure. Are there any abnormalities in the box, air valve, and baffle? Looseness or changes in position of structural members may also change local resistance.

Distinguish between drag problems and gas failure

Increased pressure difference and decreased gas handling capacity are two types of problems.

The increase in differential pressure mainly reflects airflow resistance. It may affect air volume and system operation, but does not directly indicate how much adsorption capacity is left. For specific differences, please refer to Discussion on whether the chemical filter can be replaced based on the pressure difference .

The gas handling capacity depends on the outlet concentration. If the pressure differential rises but the outlet concentration is still normal, it may just be a resistance problem, and the prefiltration or moisture source can be dealt with first. If the outlet concentration is also rising, filter replacement needs to be evaluated.

Troubleshoot abnormal outlet concentration. If the outlet concentration is higher than the inlet or fluctuates greatly, please refer to why the concentration at the outlet of the chemical filter is higher than that at the inlet . Discussion on

Don't just replace the filter material based on the pressure difference. If the increased pressure differential comes from pre-filtration or moisture problems, the same problem may recur after changing the chemical filter material.

Treatment and retesting

After locating the cause, handle it accordingly.

Pre-filtering issue. Clean or replace the pre-filter, repair and install the bypass, and record the pressure difference changes.

Moisture issues. Repair drainage, water blocking or dehumidification measures to confirm that the air entering the chemical filtration section no longer entrains droplets.

Air volume problem. If the air volume itself is high, evaluate whether the fan gear or damper needs to be adjusted. Do not cover up filter media problems by reducing air volume.

Filter material problem. If the media is confirmed to be hardened, pulverized or exhausted, replace it according to product instructions and project requirements. After replacement, check the installation seal and tightness.

Retest content. After treatment, re-measure the air volume, pressure difference and outlet concentration. Only by looking at the three together can we judge whether the problem is truly solved. 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 increased, and the site was ready to replace the filter material.

During the investigation, first check the air volume and pressure difference gauges, and no abnormalities are found. Checking the pre-filtration, it was found that the medium-efficiency filter was seriously dusty and the installation frame had a bypass. Dust enters the chemical filter section, causing the pressure difference to rise.

Treatment method: Replace the medium-efficiency filter, repair the installation frame seal, and clean the surface of the chemical filter section. After retesting, the pressure difference returned to the normal range, the outlet concentration did not change, and the filter material was not replaced.

Another item is an increase in differential pressure accompanied by fluctuations in outlet concentration. The inspection found that there was condensation in front of the filter section, and the media became damp and hardened. After the drainage and water retaining measures were repaired, the pressure difference dropped, but some media had agglomerated. The affected filter media was replaced after evaluation.

These two cases illustrate that if the pressure difference suddenly rises, check the measurement, pre-filtration and moisture first, and then judge the filter material itself. involving When selecting a chemical filter product series , it is recommended to provide the pressure difference record, air volume, temperature and humidity, 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, temperature and humidity, pre-filtration status and installation 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.