Appropriate methods for designing positive and negative differences in clean room



Maintaining a positive positive pressure in a clean room is one of the prerequisites for a clean room to be cleaned or not to maintain a clean level. Even in a vacuum-free workshop, it must maintain a positive positive pressure in adjacent rooms or suites that are not below its cleanliness level, and the cleanliness of the vacuum-cleaning workshop can be maintained.



China's plan standard [6] rules: the static pressure difference between the clean room and the clean area and the non-clean area of ​​different grades should be no less than 0.5mmH2O (~5Pa), and the static pressure difference between the clean area and the outdoor should be not less than 1. OmmH2O (~l0Pa). There are three reasons for this:



1. Positive pressure is the ability to indicate that the clean room can suppress the indoor atmosphere through the door and window loopholes, or to eliminate the purification of the infiltration room to the minimum limit when the door and window are opened, and the positive pressure to suppress the strength of the purification. Of course, the bigger the positive pressure, the better (the back will be mentioned).



2. The air volume required for positive pressure is infinite. The air volume required for positive pressure of 5Pa and positive pressure of 10Pa is only about 1 time/h. Why not do it? Obviously, the positive pressure value is lower than l0Pa.



3. United States Federal Regulations (FS209A~B): When all revenue and expenditure ports are closed, the minimum positive pressure difference between the clean room and any adjacent low-clean areas is 0.05 inches of water (12.5Pa). Has been applied in many countries.



However, the positive pressure value of the clean room is not as large as possible. According to the unit's 30 years of practical engineering tests, when the positive pressure value is ≥30Pa, it is more difficult to open the door, and the door is slightly unstable, slamming! Scary; When the positive pressure value is ≥50~70Pa, the door and window loophole will recover the whistle, and the infirm or the person with some kind of discomfort will feel uncomfortable. However, the relevant standards or specifications of many countries in the mainland and foreign countries do not have the lower limit of the positive pressure of the rule. As a result, many units only ask for the upper limit to satisfy the request, and no matter how much the lower limit is reached, the practice encountered by the author is not. The positive pressure value in the dust workshop is as high as 100Pa or more, which results in very poor results.



Data reference (portal):

Air shower: http://

High efficiency air filter: http://

Clean room: http://

High efficiency filter leak detection: http://

Operating room purification project: http://

Cleanliness level standard: http://

Cleanroom testing standards: http://

Clean factory design specifications: http://

Cleanroom management system: http://

Clean room ventilation frequency standard: http://

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