In order to prevent external pollutants from entering the clean room and increase the indoor cleanliness, it is required that the indoor pressure be kept higher than the external pressure, that is to say, in the clean room, rooms with different cleanliness must maintain a certain pressure gradient, so that a certain pressure difference can be maintained indoors Effectively prevent the clean room from being polluted or polluted by the adjacent room. The process of differential pressure debugging is to ensure the number of air changes in the clean room and the effect of equipment exhaust and dust removal, and try not to change the air supply volume and the air volume of the equipment exhaust fan and dust removal fan.
The pressure difference is adjusted mainly by adjusting the return air volume and the system exhaust air volume. The "Code for Clean Room Design" clearly states that the indoor pressure of the clean room is kept higher than the external pressure, which is called a positive pressure clean room, otherwise it is called a negative pressure clean room. Positive pressure and negative pressure are relative terms. A clean room is a positive pressure clean room to the atmosphere, but it may be a negative pressure clean room to another room. It is also stipulated that the pressure difference between clean rooms of different grades and the clean area and the non-clean area shall not be less than 5Pa, and the pressure difference between the clean area and the outside shall not be less than 10Pa.
Each functional room in the man-cleaning area should follow the man-cleaning route: unclean corridor, changing shoes, primary changing room, secondary changing room, buffer room, and clean inner corridor. Maintain a positive pressure difference of at least 30Pa between the clean room corridor and the unclean area. The basic principle of this pressure difference is that the supply air volume is greater than the return air volume, exhaust air volume, and leakage air volume to maintain positive pressure. The pressure difference is established through the balance between the air volume sent into the clean room and the exhaust air volume + differential air volume (residual air volume).
For fresh air system: fresh air volume = exhaust air volume + differential pressure air volume
For circulating air system: fresh air volume + return air volume = return air volume + exhaust air volume + differential air volume
In the final analysis, the pressure difference in the clean room, that is, fresh air volume = exhaust air volume + differential air volume, and a balanced relationship between them is established.
In short, design, construction and commissioning are three important links to ensure the normal operation of the purification system. Through commissioning, we can understand the problems that arise during the operation of the system, so that we can improve the design plan, standardize the construction operation, and avoid the above problems. The commissioning work is an important and necessary link to ensure whether the indoor pressure difference and cleanliness of the clean room are up to standard. The normal operation of the system belongs to the normal use and production process. The method of maintaining positive pressure: 1. Install an air damping layer at the air return port.
2. The exhaust pipe is equipped with an electric airtight valve medium-efficiency filter.
3. The residual pressure valve is generally located on the downwind side wall of the clean room. When taking such measures, it is required that there must be sufficient residual air volume in the room.
4. Adjust the return air valve or exhaust air valve.
5. Adjust the fresh air valve.
6. Fan and air valve interlock control.
7. Regularly replace some necessary filters.
