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The air conditioning and ventilation system of indoor controlled environments (such as GMP pharmaceutical workshops, biosafety laboratories, and chemical laboratories) needs to provide sufficient supply/exhaust air volume to the room and ensure that the room pressure difference can meet production and operational requirements. More than 20 years ago, manual air valves were mostly used in air conditioning and ventilation systems. System debugging is very time-consuming and laborious - one person is measuring the air volume at the air outlet in the room, while another person is adjusting the opening of the air valve in the ceiling; The air volume and pressure difference in one room have just been adjusted appropriately, but the adjustment of the air valves in other rooms has damaged the newly adjusted parameters; Debuggers need to make adjustments over and over again. But the good times don't last long. After the system runs for a period of time, the airtightness of the room enclosure structure, especially the door, may change, the blade position of the air valve may loosen, and the resistance of the high-efficiency filter and the air conditioning unit filter will increase. These factors all lead to changes in the air volume and pressure difference in the room. If the deviation is about to exceed the allowable value, it is necessary to readjust the air valve. In the era of self operated constant air volume dampers, a self operated air volume control valve emerged later. This type of damper uses mechanical mechanisms to "automatically" control the air volume, and has "pressure independence" within a certain range of working pressure differences. Users can set the required air volume on site. The accuracy of air volume control for ordinary self operated air valves is relatively low, with a narrow range of pressure differences that are independent of pressure, and a certain straight pipe section needs to be ensured upstream of the air valve. The Venturi air valve does not require a straight pipe section and has good pressure independent characteristics. However, Venturi valves have requirements for installation posture (horizontal installation, vertical upward, vertical downward), and it is necessary to know the installation space and air duct layout when placing an order. Self operated constant air volume valve belongs to the "feedforward" control valve that uses mechanical means. The manufacturer needs to calibrate one or more air flow operating points one by one when leaving the factory. The pollutants in the exhaust may deposit on the valve mechanism, and the characteristics of the spring material may change over time, thereby affecting the accuracy and response of air volume control. Although there are still some problems in room pressure control and long-term operation, in the era where automatic control systems have not yet become popular, self operated air valves greatly reduce the difficulty and workload of debugging. In the era of electric constant/variable air volume valves, the combination of uniform velocity tube air volume measurement devices, controllers, and electric butterfly valves has given birth to a new generation of constant air volume control valves. Due to the use of air volume measurement devices and feedback control, there is no need for factory calibration, and the accuracy of air volume basically does not change over time. (Some Venturi valves without air flow measurement devices can also achieve multi air flow operating point control through calibration, as mentioned earlier, which belongs to feedforward control.) However, the uniform velocity tube air flow measurement device requires a certain straight pipe section upstream to ensure measurement accuracy. This to some extent limits the application or on-site performance of this constant air volume valve. It should be pointed out that the names of constant air volume valves and variable air volume valves are easy to misunderstand: some people believe that constant air volume valves can only have one air volume setting value; Some people believe that a variable air volume valve can achieve multiple air volume settings. In order to facilitate technical exchange without ambiguity, we refer to air flow control valves as air flow control valves, regardless of whether there is one or the other