The basic principle of differential pressure control in clean room is to control the air supply, return air volume and exhaust air volume. When the amount of air sent into the clean room is greater than the return air and exhaust air, the room can maintain a certain positive pressure value. At this point, in the indoor and outdoor pressure differential function, through the enclosure structure is not tight, the leakage of air volume and mechanical ventilation difference.
The problem of differential pressure maintenance is that the mechanical air supply and the air volume are dynamic. For the clean air conditioning system, filter dust would increase the fresh air, air pipe resistance, thus affecting the air exhaust equipment on and off will lead to changes in exhaust volume; in addition, the outdoor corridor, and also because of changes in adjacent hot pressing, pressure effect of room pressure. Therefore, the pressure difference in the clean room needs to be checked regularly, and the valves of the new, delivery, return and exhaust routes are adjusted accordingly.
The control measures of maintaining pressure difference are as follows: (1) air return control, that is to adjust the return air quantity by changing the resistance of the louver, adjustable grille or damping layer on the return air port, so as to control the pressure of the room. This is the simplest mode of control, characterized by relatively simple structure and economy. The grille control is convenient, but the grille is not easy to be closed, and the regulation range is not large, and the direction of the air flow is also influenced. In general, the initial effect foam or the first effect non-woven fabric is used as the damping layer, and the return air quantity is adjusted by changing the resistance of the air return port, and the pressure difference between the clean indoor and the outside is controlled. With the increase of damping layer, the resistance increases and the positive pressure tends to increase. Therefore, the damping layer should be cleaned regularly and the damping layer can be reused. (2) the residual pressure valve controls the balance pressure block on the residual pressure valve by manual or automatic adjustment, and changes the valve opening of the pressure valve to realize the pressure control in the chamber. The pressure relief valve is usually located on the side wall of the clean room. When using this method, there should be enough residual positive pressure in the clean room. If the exhaust air volume changes, the residual pressure valve needs to be readjusted. The pressure valve is easy to install, but it is not closed after long-term use. If the pressure valve is completely closed, the positive pressure value is still below the required value, then other ways to control the indoor pressure difference. (3) adjust the return air valve or exhaust valve, according to the detected indoor pressure value, adjust the return air pipe (or exhaust pipe) of the electric valve, change the return air (or exhaust air), control the pressure value of the clean room. (4) the differential pressure transmitter controls the pressure of the chamber through the differential pressure transmitter, and then adjusts the new air flow. The electric valve (MD) on the OA pipe is opened (smaller).