How to troubleshoot abnormal pressure after replacing ULPA?

The filter element was replaced, but the differential pressure gauge reading was not as expected. This is common in both remodels and routine replacements.

There are two common phenomena: one is that when a new filter element is installed, the pressure difference is much lower than expected, and the site suspects that it is not installed properly; the other is that the pressure difference is higher than the old filter element, and there is suspicion that there is a problem with the product. Both of these judgments may be premature - the condition of the old filter element and the new filter element are inherently different, and direct comparison of numbers is meaningless.

The key takeaway is this: Don’t use the field readings from the old filter as a baseline for comparison with the new filter. The old filter element may be dusty, damp, or damaged, or the previous operating conditions may be different from the conditions under which the new filter element is installed. First align the comparison conditions, and then determine whether the pressure difference is really abnormal.

First align the new and old working conditions

The pressure difference is a comprehensive reflection of air volume and resistance. Before comparing the pressure difference between the old and new filters, first confirm whether the two readings were taken at the same air volume.

Is the air volume the same? After the new filter element is installed, if the fan gear does not change, but the change in the total system resistance causes the air volume to shift, the pressure difference will be different. The constant air volume system will automatically adjust the speed compensation, while the fixed speed system may experience changes in air volume. Before comparing, first measure the current air volume to confirm whether it is comparable to the air volume when the old filter element was running. For the specific air volume change rules, please refer to the relevant instructions on air volume changes after dust accumulation.

Are the operating modes consistent? The equipment may be in production mode, standby mode or debugging mode, and the air volume and pressure difference in different modes are inherently different. Record the operating mode and compare in the same mode.

Whether environmental conditions have changed. Changes in temperature and humidity will affect gas density and filter material status. Although the magnitude of the impact is usually not large, if there is a significant difference across seasons or environmental conditions before and after replacement, you should also pay attention when comparing.

Are there any changes to the pressure pipeline? If the pressure pipe is moved when replacing the filter element, the pipe may be pressed, bent or connected incorrectly. First confirm that the pressure pipeline is in normal condition, and then judge the pressure difference data. For the specific definition of measuring points, please refer to the relevant instructions for differential pressure measuring points.

After checking these items, compare the pressure difference of the new filter element with the product curve. If the on-site air volume and test conditions are consistent, the readings should be within the range corresponding to the curve. The deviation is considered an abnormality and shall be judged according to the tolerance agreed upon by the project.

What may be the reason for low pressure difference?

The pressure difference of the new filter element is obviously low, and there are several directions for investigation.

The filter element is not installed properly. The filter element is not completely seated in the installation frame, or the pressing parts are not pressed evenly, and the airflow may bypass part of the filtering surface through the gaps. In this state, the effective filter area is reduced and the pressure difference reading is low. Check the installation status and confirm that the four sides are pressed evenly.

The sealing gasket or liquid tank does not fit properly. Gasket displacement, insufficient liquid tank sealing fluid, or improper sealing structure may cause bypass air leakage. For the inspection method of liquid tank fit, please refer to the instructions related to the knife edge size.

Pressure pipeline problem. If the pipe falls off, leaks, or is connected incorrectly, the reading will deviate from reality. Especially if the pressure pipe is touched when replacing the filter element, the possibility of this type of problem is higher.

The resistance of the new filter element itself is low. If the effective filtration area of ​​the new filter element is larger than that of the old filter element, or the structure is different, the resistance may indeed be lower. In this case, it is normal for the pressure difference to be low, but you should pay attention to whether the air volume increases and whether the fan gear needs to be adjusted. involving ULPA ultra high efficiency filter or The selection of HEPA high-efficiency filter can be compared with the resistance curve of the corresponding model.

Low differential pressure is not always a problem, but sealing and measurement factors must be eliminated first. If it is confirmed that the resistance of the product itself is low, just record a new baseline and no special treatment is required.

What may be the reason for the high pressure difference?

The pressure difference of the new filter element is higher than expected, and the investigation direction is different.

The resistance of the new filter element is already high. When upgrading from HEPA to ULPA, or replacing ULPA with a different structure and different filter materials, the resistance may increase. This is a difference at the selection level, not a malfunction. For the calculation method, please refer to the instructions related to the fan operating point.

The installation is skewed or pressed too hard. Improper installation of the filter element, excessive pressing force, deformation of the frame, or pressure on the filter material may increase resistance. Check whether the outer frame is deformed and whether the filter material is pressed out.

The packaging film was not removed cleanly. Some filters have a protective film that needs to be completely removed before installation. Residual film can significantly increase drag.

There is obstruction upstream. If there are foreign objects, packaging debris or other structural parts in front of the filter element blocking part of the ventilation surface, it is equivalent to reducing the effective area and the pressure difference will increase.

The pressure tube is clogged. A clogged pressure tube can cause sluggish or high readings. Check whether the pipeline is smooth.

The air volume is on the high side. If the resistance of the new filter element is low, the air volume of the system may increase, and the pressure difference will also change accordingly. Confirm the air volume and fan speed, and compare them with when the old filter element was running. Supporting FFU fan filter unit system, unit gear change is a common reason; equipment-side applications such as EFU equipment end fan filter unit , changes in equipment operating status will also affect the pressure difference.

Complete new baseline recording

Regardless of whether the pressure difference is high or low, as long as the installation and measurement are confirmed to be normal, a new operating baseline should be established.

Record the initial resistance and corresponding air volume of the new filter element. This is the starting point for subsequent comparisons. Do not take the pressure difference value of the old filter element after dust accumulation as the standard for the new filter element. The two benchmarks are different.

Check the resistance curve. Use the air volume and pressure difference measured on site and compare it with the resistance curve of the product to confirm that it is within a reasonable range.

Complete on-site leak detection. The sealing status may change after replacing the filter element, and leak detection is a necessary step to confirm the integrity. Leak detection records are stored corresponding to the product number and installation location.

Update maintenance ledger. Record the replacement date, new filter element model, number, initial resistance and air volume. During the next maintenance, these data will be used as a reference to judge changes in the status of the filter element.

Keep following trends. After running for a period of time, compare the pressure difference changes to determine whether the dust accumulation speed of the new filter element is normal. If the differential pressure rises too quickly, go back and check the upstream load or system conditions. involving HEPA/ULPA air filters have the same record content. Products of different grades of

Project judgment example

The original H14 filter element of a certain equipment was replaced with U15 after one year of operation. After replacement, the reading of the differential pressure gauge was about 40% higher than before.

The first reaction of the operation and maintenance team was to suspect that the resistance of the new filter element exceeded the standard. When troubleshooting, first check the air volume: the fan gear is the same before and after replacement, and the measured air volume is basically the same, ruling out changes in working conditions.

Then compare the product information: the initial resistance of U15 at the target air volume is about 30% to 35% higher than that of H14. The 40% deviation measured on site is slightly higher than the data value, but considering that the old filter element has accumulated dust and the pressure difference at that time included part of the dust contribution, the actual difference may be within a reasonable range.

Further inspection of the installation status and pressure pipeline found no abnormalities. Final judgment: The increase in pressure difference mainly comes from the grade difference and is within the expected range. Record the new initial resistance data and include it in the maintenance ledger.

The key to this case is: first eliminate working conditions and installation factors, and then judge the product itself. If you directly judge the product problem based on 'the pressure difference is 40% higher' at that time, you may take a detour.

Selection and Acceptance Checklist

About Aili Industrial’s replacement package

The abnormal pressure difference after replacing the filter element often comes from the difference in specifications between the old and new filter elements, rather than a product problem. Aligning the specifications during the selection stage and recording according to the new baseline after replacement can reduce this type of misjudgment.

Aili Industry has independent manufacturing capabilities in filters, fans, control systems and sheet metal processing, and can provide ULPA ultra high efficiency filter、HEPA high-efficiency filter and supporting air supply equipment. For replacement projects, the original system parameters, new filter element specifications and target air volume can be combined to help check the resistance matching. When the filter is matched with equipment such as FFU and EFU, the impact of the resistance difference between the old and new filter elements on the fan operating point can also be evaluated together during the planning stage.

When enquiring, provide the original filter element model, operating data, reason for replacement and target operating conditions to help confirm the appropriate replacement solution. The specific configuration is subject to the technical documents confirmed by the project and the on-site measurement results.