Can the chemical filter be replaced based on the pressure difference?

Direct answer: Don’t just look at the pressure difference. The pressure difference can reflect the air flow resistance, but does not directly reflect the gas handling capacity.

This distinction is critical in operations and maintenance. The pressure difference increases after the particle filter accumulates dust, so the replacement basis is relatively intuitive. Chemical filters are different. After the medium is absorbed or consumed by reaction, the outlet concentration may gradually increase, but the pressure difference may not change much during the lifetime. If you only wait for the pressure difference alarm to change, the outlet may have already exceeded the standard.

Conversely, an increase in pressure differential is not necessarily a sign of media consumption. Prefilter blockage, moisture hardening, and filling displacement may cause the pressure difference to increase, but the gas processing capacity may not reach the point of replacement. Changing the filter material in the wrong direction wastes costs and does not solve the fundamental problem.

Pressure difference reflects flow resistance

Let’s first explain the role of pressure difference clearly.

The pressure difference is the pressure difference before and after the filter section, which reflects the resistance of air flow through the filter section. The greater the air volume, the denser the filter material, the narrower the channel, the higher the pressure difference.

In chemical filters, differential pressure can be used to:

• Find out if the filter section is clogged or damp

• Determine if pre-filtration requires maintenance

• Monitor the impact of changes in air volume on the system

But the pressure difference cannot tell you:

• How much adsorption capacity is left in the medium?

• Whether the outlet concentration can still meet the requirements?

• Whether the target gas has begun to penetrate

For specific troubleshooting methods for increased pressure difference, please refer to Discussion of what to check if the pressure difference before and after the chemical filter suddenly rises .

Gas capabilities require corresponding evidence

Determining whether the chemical filter should be replaced depends on the gas processing capacity.

The export concentration trend is the most direct basis. The efficiency is usually higher when new filter material is put in. As the running time increases, the outlet concentration may gradually increase. When the outlet concentration approaches or exceeds the allowable value of the project, replacement should be considered.

Residual capacity detection can also be used to assist judgment. If conditions permit, the remaining capacity of the filter material can be evaluated to understand how long it can last. For specific life assessment, please refer to Discussion of how long chemical filters last .

The penetration curve can reflect the change of outlet concentration with time or cumulative load. Trends tell a better story than single data. For specific concepts, please refer to Discussion of what breakthrough concentration means in a chemical filter report .

Smell can be used as a reference, but it cannot be used as the only criterion. Some gases have no obvious odor, and some gases have an impact on the process at low concentrations. For specific differences, please refer to Discussion of whether chemical filters can remove ammonia from the air .

Protect system operation at the same time

Even if the gas effect is acceptable, excessive resistance may affect the air volume.

If the pressure difference increases causing the air volume to decrease, the system may not be able to maintain the designed air supply volume. In this case, even if the outlet concentration is still normal, the resistance problem still needs to be dealt with.

Directions may include: cleaning or replacing the pre-filter, repairing the moisture problem, and adjusting the damper or fan speed. If the resistance problem comes from the chemical filter section itself, the filter media may need to be replaced. For specific troubleshooting methods, please refer to Discussion of what to check if the pressure difference before and after the chemical filter suddenly rises .

Even if the pressure differential is normal, the outlet may no longer meet the requirements. The two types of problems require separate measures, and we cannot just focus on one indicator.

How to determine replacement criteria

The replacement criteria for chemical filters are recommended based on several conditions.

outlet concentration. Arrange replacement when the replacement threshold agreed upon by the project is reached. The threshold corresponds to the protection target, not the penetration criterion in the test report. For specific differences, please refer to Discussion of what breakthrough concentration means in a chemical filter report .

Remove efficiency trends. The outlet concentration continues to increase and the removal efficiency decreases, indicating that the medium is approaching the end of consumption. For specific calculations, please refer to Discussion on how to calculate the removal efficiency of chemical filters .

Cumulative load. Combined with the inlet concentration, air volume and operating time, estimate how much pollutants the filter material has processed. When the cumulative load approaches the media capacity, arrange replacement in advance.

Differential pressure changes. If the pressure difference rises significantly, investigate the cause first. If it's a pre-filtration or moisture issue, deal with the front end first. If it is confirmed that the resistance of the filter material itself is abnormal, then evaluate and replace it.

Operation record. The reason, date and operating conditions for each replacement should be recorded. This information can help optimize the next replacement plan. For specific management methods, please refer to Discussion on why the chemical filter replacement cycle cannot be calculated as half a year .

Project judgment example

The pressure difference of the chemical filter of a certain project has been stable for a long time, and the operation and maintenance personnel believe that it does not need to be replaced. It was not until the equipment showed signs of corrosion that the outlet concentration was detected and found to have exceeded the standard.

In another project, the filter material was directly replaced after the pressure difference increased, but the pressure difference was still high after replacement. The investigation found that the pre-filtration section was heavily dusted and a bypass was installed. Dust entered the chemical filtration section, causing resistance to rise. After cleaning the pre-filter and repairing the installation, the pressure difference returned to normal, and the new filter material was not replaced.

These two cases illustrate that stable pressure difference does not mean sufficient gas capacity, and rising pressure difference does not necessarily indicate a problem with the filter material. involving When selecting a chemical filter product series , it is recommended to provide the outlet concentration data, pressure difference records and operating conditions to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s replacement criterion package

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 the formulation of replacement criteria, the target gas, outlet requirements, operating data and testing plans can be combined to assist in checking maintenance and replacement methods.

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