Why is the differential pressure unstable in modular cleanrooms?

I. Air Leaks at Module Joints: The Most Common "Hidden Flaw"

Modular cleanrooms are constructed from prefabricated panels, and the airtightness of their joints is the weakest link in the entire enclosure structure. Statistics show that over 70% of pressure differential instability problems originate here.

Key areas to check include:

Joints between wall panels, between wall panels and ceiling panels, and between ceiling panels.

The installation frames of pass-through windows, observation windows, and HEPA filters.

The areas around openings through the enclosure structure, such as those for lighting fixtures, conduits, and fire detectors.

The sealing strips between door frames and wall panels.

Typical symptoms: Large fluctuations in pressure differential, with rapid drops, and difficulty stabilizing even after closing all doors and windows. If this occurs, use a smoke pen or thin cotton thread to test the joints to find the leak point, then reapply sealant or install additional sealing strips.

II. Imbalance Between Supply and Exhaust Air Volume: A System-Level "Power Imbalance"

Pressure differential is essentially the pressure generated by the difference between the supply air volume and the return/exhaust air volume. When this difference changes, the pressure differential naturally fluctuates. Airflow imbalance is usually caused by the following reasons:

1. Damper and Inverter Issues: The opening of regulating valves on the supply, return, and exhaust ducts may be incorrectly adjusted, or the inverter parameters controlling the fan speed may be improperly set or have a delayed response, leading to fluctuating airflow.

2. Filter Clogs: After a period of use, the resistance of pre-filters, medium-efficiency filters, and high-efficiency filters gradually increases. When the resistance rises to a certain level, the actual airflow will significantly decrease, a common reason for the pressure differential "slowly dropping."

3. System Design Defects: In a multi-room shared air conditioning system, if reasonable zoning or constant airflow valves are not installed, adjusting the airflow in one room will "steal" airflow from other rooms, causing mutual interference and cross-pressure in the entire system's pressure differential.

Typical Manifestations: The pressure differential fluctuates wildly and irregularly; or after people enter or exit, the pressure differential takes a long time to return to the set value.

III. Personnel and Operational Disturbances: "Human Interference" in Dynamic Operation

This is the most common dynamic cause, directly related to the operator's habits, and is also the most easily overlooked factor.

1. Frequent Door Openings

Each door opening instantly disrupts the room's pressure balance. Especially in buffer rooms, if two doors are opened simultaneously, creating a "through draft," the pressure differential can instantly drop to zero or even cause backflow.

2. Airflow Disturbances

When personnel move quickly, turn around, or move items within the workshop, they disrupt the originally stable unidirectional or non-unidirectional airflow, causing temporary pressure fluctuations near the differential pressure sensor.

Typical Manifestation: Pressure differential fluctuations are highly correlated with the rhythm of personnel activity; stable when no one is present, but fluctuating when someone is operating. These problems require more management intervention, such as strengthening the standardized use of interlocking doors and controlling the number of people entering the workshop simultaneously.

IV. Control System and Instrument Failures: Misleading "Judgment Basis"

Sometimes the problem does not lie in the purification system itself, but in the monitoring and control环节. Incorrect readings can lead maintenance personnel to misjudge the nature of the problem, wasting significant troubleshooting time.

1. Sensor Issues: Improper installation of the differential pressure sensor (e.g., directly facing the air supply or return vent), blocked or leaking pressure lines, or the sensor itself not being calibrated periodically or experiencing zero-point drift can all cause erratic readings that do not match the actual pressure.

2. Actuator Failure: If the electric actuator controlling the opening of the air valve is stuck, has worn gears, or has lost feedback signals, the system may display that it is adjusting, but the valve is not actually moving, and the airflow will not change.

Typical Symptoms: The differential pressure value on the panel fluctuates erratically, but no noticeable change can be felt by hand feeling the airflow at the door seam or observing the direction of the door curtain's movement. In this case, a differential pressure gauge should be used on-site for comparative measurement to confirm whether the problem is with the instrument or the system.

Quick On-Site Troubleshooting Guidelines

To facilitate rapid problem location by on-site personnel, troubleshooting can be conducted according to the specific manifestations of differential pressure fluctuations, following these directions:

Conclusion

Instant differential pressure in modular cleanrooms is rarely caused by a single factor; more often, it is the result of multiple factors combined. It is recommended to establish the following mechanisms in daily management: regularly conduct airtightness checks using smoke generation or ultrasonic leak detectors; periodically clean or replace filters at all levels; calibrate differential pressure sensors quarterly; and provide operators with standardized training on the use of interlock doors. Only by combining hardware maintenance with personnel management can the problem of unstable differential pressure be fundamentally solved.