News Center
Your current location：Home > News CenterNews Center
Cleanroom pressure differential requirements and control
2026/5/25
Air always flows from areas with a higher absolute pressure difference to areas with a lower absolute pressure difference. Therefore, we must ensure that the higher the cleanliness level of a room, the higher the absolute pressure difference; and the lower the cleanliness level of a room, the lower the absolute pressure difference. In this way, when the clean room is operating normally or the airtightness of the room is compromised (such as opening the door), the air can flow from the area with higher cleanliness to the area with lower cleanliness, so that the cleanliness of the high-cleanliness level room is not contaminated or interfered with by the air from the lower-level room.
1. Pressure Difference and Air Exchange Rate
The air change rate of the clean room has no relation to the pressure difference between the clean room and the outside. The air change rate is the quotient of the total incoming air volume in a certain clean space divided by the volume of the space. The more pollutants there are in the space and the higher the cleanliness level, the more air changes are required. The pressure of the space is the excess amount of incoming air volume over the return air volume to maintain a certain pressure level. The pressure difference is the difference in pressure between adjacent spaces.
II. Maintenance of Pressure Differential Stability
1. Filter system management:
Regularly replace the fresh air filter to reduce the pressure drop caused by the blockage of the fresh air filter. Regularly replace the primary and secondary filters to minimize the pressure fluctuations caused by the changes in the supply air volume.
2. Door Opening and Closing Management:
Do not open and close the door frequently, as this may cause the self-control system to repeatedly adjust and result in malfunction and pressure imbalance. Reduce the time for each door opening and closing to prevent air leakage and a pressure drop exceeding the system's adjustment range. The door must be closed tightly; otherwise, excessive air leakage will cause pressure imbalance. Using automatic doors allows for setting the opening time, holding time, and closing time, ensuring that the pressure difference is not greatly affected by fluctuations.
3. Daily Inspection:
Regularly check the sealing performance of each door. Regularly inspect the pressure differential devices and display data on site. Continuously monitor the data of the online pressure differential display system, keep abreast of the on-site conditions at any time, and promptly alert the operators to pay attention to maintaining the stability of the pressure differential.
III. Measures for Maintaining Pressure Difference
Basic principle: In general, the ventilation system mostly adopts a constant air volume mode. That is, it first ensures that the air supply volume of the cleanroom remains relatively constant, and then adjusts the return air volume or exhaust air volume of the cleanroom to control the pressure difference air volume of the cleanroom and maintain the pressure difference value of the cleanroom.
The measures taken:
Manual double-leaf regulating valves or butterfly valves were installed on the return and exhaust ducts of the clean room to control the volume of return and exhaust air and to regulate the indoor pressure difference.
During the debugging of the air conditioning system, the pressure difference in the clean room should be adjusted properly. During the operation of the air conditioning system, if the pressure difference in the clean room deviates from the set value, it will be more troublesome to make the adjustment.
At the return (exhaust) air outlets of the clean room, damping layers (such as single-layer non-woven fabric, stainless steel filters, aluminum alloy filters, nylon filters, etc.) are installed, which can effectively ensure the positive pressure of the clean room. However, the filter nets used as the damping layers need to be replaced frequently to prevent the positive pressure in the clean room from being too high.
Residual pressure valves are installed on the partition walls of adjacent rooms to control positive pressure. The advantages are that the equipment is simple and reliable. However, the disadvantage is that the size of the residual pressure valves is relatively large, resulting in limited ventilation volume, making installation inconvenient and also making it difficult to connect with the ventilation ducts.
An electric actuating system is installed on the valve shaft of the return (exhaust) air branch pipe of the clean room, thereby forming an electric regulating valve in conjunction with the corresponding valve. Based on the feedback of the clean room pressure difference value, the valve opening is finely adjusted to automatically regulate the pressure difference in the clean room to the set value. This method is used to control the pressure difference in the clean room reliably and accurately, and is widely applied in engineering practice. This system can be installed on the return (exhaust) air branch pipe regulating valve of the clean room or typical clean rooms where the pressure difference needs to be displayed.
Vortex flow control valves are installed on the supply and return (exhaust) air ducts in the clean room. There are three types of vortex valves - constant flow rate valves, which provide a stable air flow; dual-stable valves, which offer two different air flow rates, namely the maximum and minimum; and variable flow rate valves, which can control the air flow by closing-loop control based on an instruction response of less than 1 second and flow feedback signals. The vortex valves have the characteristics of being unaffected by changes in duct pressure, rapid response (less than 1 second), and precise adjustment. However, the equipment is relatively expensive and is suitable for use in situations where high precision and reliability of system pressure difference control are required. By using constant flow rate valves and dual-stable valves, the supply and exhaust air volumes in the clean room can be strictly controlled, thereby forming a stable pressure difference air volume and controlling the pressure difference stability of the clean room. Using supply air variable flow rate valves to regulate the room, and having the supply air valve flow track the flow of the exhaust air valve, can form a stable pressure difference air volume and control the pressure difference stability of the clean room. Using supply air constant flow rate valves and exhaust air variable flow rate valves to regulate the room, having the exhaust air valve track the changes in room pressure difference and automatically adjust the room pressure difference, can form a stable pressure difference air volume and control the pressure difference stability of the clean room.
