Cleanroom Differential Pressure Control and Positive Pressure Maintenance Methods

As a core control parameter in cleanrooms, differential pressure directly influences airflow direction and the effectiveness of contamination containment, thereby playing a pivotal role in the overall environmental control of the facility.

The cleanroom differential pressure primary function is to prevent contamination. Since the airtightness of a cleanroom cannot be absolutely perfect, air naturally flows from areas of higher pressure to those of lower pressure, carrying contaminant particles along with it. Furthermore, airflow disturbances caused by opening doors and the movement of personnel can easily lead to the contamination of clean zones. Consequently, cleanrooms must maintain an appropriate differential pressure relative to their surrounding areas: a positive pressure state minimizes the ingress of external dust, while a negative pressure state prevents harmful internal dust from contaminating adjacent zones, thereby safeguarding the integrity of the clean environment.

Establishing the required differential pressure in a cleanroom necessitates a process of systematic testing and commissioning, primarily involving the adjustment of airflow volume, cleanliness levels, and differential pressure. Airflow commissioning is conducted in accordance with design blueprints. Cleanliness testing is categorized into three operational states—"as-built," "at-rest," and "in-operation". The core objective of differential pressure commissioning is to maintain the required pressure gradient and prevent cross-contamination. During this process, efforts are made to avoid altering the supply airflow volume or the exhaust volume from process equipment; instead, the differential pressure is primarily established by adjusting the return airflow volume and the system's general exhaust volume.

The internal pressure of a positive-pressure cleanroom must be higher than that of the external environment, while a negative-pressure cleanroom operates in the reverse manner. Furthermore, the differential pressure between clean zones of different classifications—as well as between a clean zone and a non-clean zone—must be no less than 5 Pa; the differential pressure between a clean zone and the outdoor environment must be no less than 10 Pa. Personnel purification zones must maintain an appropriate pressure gradient, sequenced from the non-clean corridor to the clean inner corridor; specifically, the clean inner corridor must maintain a positive pressure of at least 30 Pa relative to the non-clean zone. The fundamental principle underlying the establishment of differential pressure is that the supply airflow volume must exceed the sum of the return airflow volume, the exhaust airflow volume, and the air leakage volume. Regardless of whether a system utilizes 100% fresh air or recirculated air, the final configuration must satisfy the equilibrium equation wherein the fresh air intake volume equals the sum of the exhaust airflow volume and the airflow volume required to maintain the differential pressure. The differential pressure within a cleanroom is susceptible to interference from a variety of factors. Fluctuations in outdoor wind pressure and velocity, a reduction in supply air volume caused by increased resistance in the HVAC system's filters, and a deterioration in sealing integrity resulting from personnel movement and the frequent opening of doors and windows—all can compromise the stability of the differential pressure. To maintain positive pressure, six specific measures may be implemented: installing air damping layers at return air vents; fitting exhaust ducts with motorized airtight valves and medium-efficiency filters; positioning residual pressure valves on the downstream walls of the cleanroom; adjusting return air or exhaust valves; adjusting fresh air valves; and establishing an interlock control system between the fans and the air valves.

Mastering the control mechanisms for cleanroom positive pressure—and executing the design and commissioning phases with precision—is fundamental to ensuring the system operates stably and energy-efficiently, thereby meeting the clean environment requirements of modern industrial production. This necessitates aligning the cleanroom's cleanliness classification with the specific characteristics of the industry, while strictly adhering to standardized design and construction protocols to guarantee that the cleanroom environment consistently meets regulatory standards.

Suzhou Pharma Machinery Co.,Ltd.

2026/05/04

Icey