Venturi constant air volume valve (CAV): The core device for high-precision airflow control
I. Core Definition and Design Basis of Venturi Constant Air Volume Valves
Venturi constant air volume valves are an important category within the Venturi valve family, belonging to pressure-independent air volume control devices. Their core function is to automatically maintain a constant set air volume output when the static pressure in the duct fluctuates, requiring no additional power drive (purely mechanical) or only simple manual adjustment to achieve precise air volume control. Their design is based on the Venturi effect—a fluid dynamics phenomenon discovered by the Italian physicist Giovanni Battista Venturi. Specifically, when a confined fluid passes through a narrowed cross-section (throat), its velocity increases significantly, while the static pressure decreases accordingly. Furthermore, the velocity is inversely proportional to the cross-sectional area. This effect allows for precise airflow control.
Compared to ordinary constant air volume (CAV) valves, the Venturi constant air volume valve, relying on a streamlined hyperboloid valve body design and optimized aerodynamics and structural mechanics, achieves significant improvements in airflow control accuracy, response speed, and quietness. It is particularly suitable for scenarios requiring high airflow stability and control precision, making it an upgraded replacement for traditional CAV valves.
II. Working Principle of the Venturi Constant Air Volume Valve
The working logic of the Venturi constant air volume valve is based on a combination of the Venturi effect and mechanical balance. Its core principle is to adaptively adjust and offset static pressure fluctuations in the ductwork to maintain a constant airflow. The specific process can be divided into three key stages:
1. Application of the Venturi Effect
The valve body adopts a streamlined contraction-expansion structure. When airflow passes through the throat of the valve body (the point of minimum cross-sectional area), the flow velocity increases sharply and the static pressure decreases, creating a pressure difference between the throat and the valve body inlet and outlet. This pressure difference acts as the regulating force, driving the valve core to move axially, thereby adjusting the throat cross-sectional area and achieving dynamic balance of airflow.
2. Mechanical Adaptive Adjustment Mechanism
The Venturi constant air volume valve incorporates a precision spring and a conical valve core, forming a purely mechanical adjustment system that achieves automatic adjustment without power supply. When the static pressure in the duct increases, the airflow pressure on the valve core increases, compressing the spring and causing the valve core to move towards the throat, reducing the flow cross-section and decreasing the airflow to offset the increased airflow caused by the increased static pressure. When the static pressure in the duct decreases, the spring returns to its original position, the valve core moves in the opposite direction, increasing the flow cross-section and increasing the airflow to compensate for the insufficient airflow caused by the decreased static pressure. This dynamic balance ensures that the airflow through the valve remains at the preset value regardless of fluctuations in the duct static pressure.
3. Airflow Calibration and Precise Positioning
Before leaving the factory, each Venturi constant air volume valve undergoes calibration at no fewer than 50 airflow points to ensure accurate airflow control. During field use, the preset airflow can be adjusted manually by adjusting the actuator and the N pre-set calibration airflow points according to actual needs, achieving precise airflow positioning without the need for complex on-site commissioning procedures, significantly improving construction efficiency.