What is the reason for the sudden decrease in ULPA pressure difference?

An increase in pressure difference makes people nervous, but a decrease in pressure difference is easy to be ignored - some people may think, 'Isn't it a good thing if the resistance is less?'

uncertain. A sudden drop in pressure differential may result from a drop in fan air volume, filter element replacement, instrument abnormalities, or system bypass. The latter two need to be taken seriously: bypass air leakage means that unfiltered air bypasses the ULPA, and the actual protection capability of the clean side may have been compromised. For specific troubleshooting methods, please refer to the relevant instructions on pressure difference increase. The two judgments are logically connected.

First distinguish between air volume and resistance changes

This is the first step in the investigation, and it is also the most likely place to go wrong.

When the air volume decreases, the pressure difference naturally decreases. Stopping the fan, closing the air valve, reducing the rotational speed, and switching the system to duty mode will all reduce the air volume passing through the filter element. The decrease in the reading of the differential pressure gauge is the result of changes in working conditions, not an improvement in the condition of the filter element.

The way to judge is to look at the air volume and pressure difference together. If both decrease simultaneously, check the fan, damper and control status first. If the air volume is approximately unchanged but the pressure difference is significantly reduced, you need to suspect the filter element or sealing link.

In matching FFU fan filter unit system, group control gear adjustment is a common reason. In the Device-side applications such as EFU equipment side fan filter unit , equipment operating mode switching will also affect the air supply volume. The pressure difference fluctuation caused by such changes in working conditions does not require replacement of the filter element.

Check measurement link

After confirming that there is no change in the working conditions, the next step is to check the measurement link.

Pressure pipe. If the pressure guide tube falls off, leaks, is connected incorrectly or is blocked, the reading will deviate from the actual value. Check whether the high and low pressure side connections are correct and whether the pipeline is damaged.

Instrument zero point. After long-term operation, the zero point of the differential pressure gauge may drift. Compare with a standard instrument or check the zero point status according to the instructions. If the gauge itself reads low, the actual differential pressure may be normal.

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

Measuring point location. The reading may also change if the pressure tap or line routing has been recently adjusted. Confirm that the measuring point has not changed, or record the new measuring point position as a baseline. involving For HEPA/ULPA air filter products of different grades, the measurement link inspection methods are the same.

Check filter element and installation status

The measurement is normal, the working conditions are stable, and the pressure difference has indeed decreased. At this time, focus on checking the filter element and seal.

Has the filter element been replaced? If you have recently replaced a new filter element, the resistance of the new filter element may be lower than the original old filter element, and it is normal for the pressure difference to decrease. Especially when upgrading from HEPA to ULPA, if the new filter element has a larger effective area or a different structure, the resistance may be lower. Record the filter element model and resistance data before and after replacement to facilitate judgment.

Is the filter element installed in place? The filter element is not completely seated in the installation frame, or the pressing parts are not pressed evenly, and the airflow may bypass the gap. This type of problem will reduce the effective filter area and cause the pressure difference reading to be low.

Whether the seal has failed. Gasket displacement, lack of sealing fluid or aging of the liquid tank seal will lead to bypass air leakage. For the method of checking the fitting status of the liquid tank seal, please refer to the relevant instructions.

Whether the filter material is damaged. When the filter material has holes or tears, the air passes through the damaged area in a short circuit and the resistance decreases. Such damage may result from foreign object impact during transportation, installation or operation.

Bypass leaks need to be taken seriously. As the pressure differential decreases, the particle concentration on the clean side may increase. On-site leak detection is a necessary step to confirm the sealing status, and cannot be judged based on the pressure difference alone. For specific troubleshooting methods, please refer to the relevant instructions for inspection after reverse installation.

How to create a new baseline after replacement

If it is confirmed that the pressure difference is reduced due to filter element replacement, the operating baseline needs to be re-established.

Record the initial resistance of the new filter element. Measure and record at the same air volume as a starting point for subsequent comparisons.

Check the resistance curve of the new filter element. Compare it with the data on the product information to confirm that the on-site reading is within a reasonable range.

Reconfirm the air volume and face speed. Changes in filter element resistance may affect the system operating point, so it is necessary to confirm whether the air supply volume still meets the design requirements. involving ULPA ultra high efficiency filter or For the selection of HEPA high-efficiency filters , please refer to the corresponding product information.

Complete on-site leak detection. The sealing status after replacement needs to be re-confirmed, and leak detection records must be saved corresponding to the product number and installation location.

Update maintenance ledger. 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.

Project judgment example

During the operation of a certain equipment, the ULPA pressure difference dropped from 200 Pa to 120 Pa. The first reaction at the scene was that the filter element might be damaged.

When troubleshooting, first look at the operation records: at the same time, the equipment switched from production mode to standby mode, and the fan speed automatically decreased. After the air volume decreases, the pressure difference decreases, which is normal and is not a problem with the filter element.

When the equipment is restored to production mode, the pressure difference returns to about 195 Pa, which is basically the same as before the switch. This shows that the filter element is in normal condition and the change in pressure difference comes from the switching of operating modes.

Another situation: If the air volume does not change, but the pressure difference decreases, and on-site leak inspection finds leaks in the frame, then the sealing problem needs to be dealt with instead of replacing the filter element. The order of judgment is: first look at the working conditions, then look at the instrument, and finally check the filter element and seal.

Selection and Acceptance Checklist

About Aili Industrial’s pressure difference investigation cooperation

To investigate the sudden decrease in pressure difference, operating data, product parameters and sealing status need to be judged together.

Aili Industrial's manufacturing system covers filters, motors, fans, control systems and complete machine assembly, and can provide HEPA/ULPA products of different grades and supporting air supply equipment. filter with FFU fan filter unit、When the EFU equipment-end fan filter unit is matched in the same system, the filter element resistance and fan operating point can be calculated together during the planning stage to facilitate comparison and judgment during operation.

When the pressure difference is abnormally low on site, it is recommended to record the air volume, rotation speed and pressure difference readings first, and then contact the supplier for verification after completing the on-site leak detection. The specific handling method shall be subject to on-site inspection results and project maintenance requirements.