Variable Air Volume Venturi Valve

Product Model	VAV Venturi Variable Air Volume Valve
Category	Laboratory Products
Reference Price	Price on request

Hot Customizable for Working Conditions 10 Technical Parameters

Product Overview

The Variable Air Volume (VAV) Venturi Valve,Abbreviation VAV Venturi Valve, is the core control device for laboratory variable air volume ventilation systems, installed on the exhaust branch pipe of fume hoods. It enhances the Venturi valve body with an airflow measurement section, a differential pressure sampling tube, a controller, and an electric actuator. The built-in measurement section detects the exhaust airflow in real time. The differential pressure signal is transmitted from the sampling tube to the controller's sensor. The control chip compares the measured airflow with the target airflow and commands the actuator to drive the valve core (blade) to rotate and change the opening degree, allowing the exhaust airflow to follow the fume hood sash opening, maintaining a constant sash face velocity.

When the fume hood sash is pushed up or down, the opening area changes continuously. In a constant airflow system, the exhaust airflow remains constant, resulting in higher face velocity and energy waste when the sash is closed, or potentially below safe levels when the sash is open. The VAV Venturi Valve automatically increases the exhaust airflow when the sash is opened and decreases it when the sash is closed, using a sash position sensor or a face velocity control mode, keeping the face velocity within a safe range. This ensures harmful gases are not released while significantly reducing exhaust airflow when the sash is closed, saving air conditioning fresh air and fan energy. It is the mainstream solution for modern laboratory ventilation control.

The VAV Venturi Valve body supplied by Xicheng Environmental Protection is made of fireproof and flame-retardant materials, corrosion-resistant, and suitable for acid and alkali exhaust environments. The controller supports displacement control and face velocity control modes, with airflow display, fault alarm, and building communication interface. The actuator responds quickly and adjusts stably, and can be integrated with variable frequency exhaust fans, fresh air systems, and laboratory monitoring systems to achieve intelligent and energy-efficient operation of fume hood exhaust.

Working Principle

The working process of the VAV Venturi Valve is a rapid closed-loop control. Airflow enters the valve and first passes through the built-in airflow measurement section. The measurement section utilizes Venturi throttling or multi-point velocity measurement to generate a differential pressure corresponding to the airflow. The sampling tube transmits the differential pressure signal to the differential pressure sensor on the controller. The chip calculates the real-time exhaust airflow based on the differential pressure. The controller also receives signals from the fume hood sash position sensor or face velocity setting to calculate the required target exhaust airflow for the current sash opening.

When the measured airflow differs from the target airflow, the control chip outputs a command to drive the electric actuator, which moves the valve core or adjusts the blade to change the valve's flow area: if the airflow is too high, it closes the valve; if too low, it opens it. This continues until the measured airflow returns to the target value. The entire measurement, comparison, and execution process rapidly cycles, allowing the airflow to follow the sash movement in a very short time while maintaining a constant face velocity. The Venturi valve body's flow channel characteristics ensure a stable relationship between the valve core opening and airflow, and strong resistance to network pressure fluctuations. The fireproof and flame-retardant valve body and corrosion-resistant measurement components ensure long-term contact with acid and alkali exhaust without corrosion or measurement drift, guaranteeing control accuracy and reliability.

Structural Components

The VAV Venturi Valve consists of a Venturi valve body, adjustable valve core or blade, airflow measurement section, differential pressure sampling tube, controller, electric actuator, and interfaces. The valve body is a cylindrical Venturi shape, made of fireproof and flame-retardant engineering materials, corrosion-resistant, with circular interfaces at both ends for connection to air ducts. The valve core inside is driven by the actuator to change the area of the annular flow channel.

The airflow measurement section is located in a stable airflow area inside the valve and is connected to the controller's differential pressure sensor via the sampling tube. The controller integrates a chip, display, buttons, and communication interface, installed on the valve body or nearby, receiving signals from the sash position sensor and face velocity sensor, and outputting actuator control commands. The electric actuator is directly installed on the valve shaft, with manual operation and position feedback. The system also includes a sash position sensor, face velocity sensor (for face velocity control mode), audible and visual alarm panel, and variable frequency fan linkage interface. Multiple VAV valves can be connected to the laboratory ventilation monitoring system via a communication bus.

Specification Model Table

The following table compares the control of VAV valves and CAV valves based on ventilation system type for selection.

Item	VAV Valve	CAV Valve
Exhaust Airflow	Varies with sash opening	Constant
Face Velocity	Constant at any opening	Fixed opening qualified
Energy Consumption	Energy-saving when sash is closed	Full airflow operation
Configuration	Controller and actuator	Mechanical spring

Product Features

The VAV Venturi Valve provides closed-loop air control, ensuring safety and energy efficiency, and is the core device for modern laboratory fume hood ventilation control. Its main features are as follows.

Real-time airflow measurement and closed-loop adjustment, maintaining constant face velocity
Automatic airflow reduction when sash is closed, significantly saving fresh air energy consumption
Stable Venturi measurement, strong resistance to network pressure fluctuations
Fast response, quickly following sash movement
Fireproof and flame-retardant, corrosion-resistant valve body, suitable for acid and alkali exhaust environments
Includes airflow display, fault alarm, and communication interface
Can be integrated with variable frequency fans and building automation systems

Body Material	Fireproof and Flame-Retardant Engineering Materials
Control Method	LCV Control
Measurement Components	Integrated airflow measurement section
Signal Transmission	Pressure Differential Sampling Tubing
Actuator	Electric actuator drives valve core
Control Mode	Displacement / Face Airflow Mode
Control Objective	Constant face air velocity
Corrosion resistance performance	Acid and Alkali Corrosion Resistance
Communication Interface	Optional Building Communication
Energy-saving Features	Window closure reduces airflow

Application Industries

VAV Control for Modern Chemical Laboratory Fume Hoods
VAV Ventilation Systems for Pharmaceutical R&D and QC Laboratories
Exhaust Control for Ventilation Cabinets in Wet etching Areas of Semiconductor and Panel Factories
Energy-Saving Ventilation Renovation for Testing and Certification Laboratory Labs
Centralized VFD Exhaust System for Ventilation Cabinets in University Research Buildings
Safe Ventilation for Hospital Pathology and Disease Control Laboratories
Laboratories with High Energy Consumption and Face Velocity Safety Requirements

Typical Process Locations

The VAV Venturi Valve is installed on the top of each VAV fume hood or on the exhaust branch pipe, positioned as close as possible to the fume hood exhaust outlet. Straight pipe sections are retained before and after the valve to ensure accurate measurement. Displacement sensors are installed on the viewing windows, and face velocity display and alarm devices are installed on the fume hood panels. Each VAV valve's exhaust branch pipe is connected to horizontal dry pipes and a central exhaust fan. The airflow demand of multiple valves is aggregated via a communication bus to coordinate the VFD operation of the exhaust fan, allowing the fan's airflow to vary with actual demand, achieving system-level energy savings. The fresh air system operates in VFD mode to maintain room pressure difference and supply air balance.

During installation, the valve body is installed according to the airflow direction markings. The sampling gas pipe connections are correct and airtight, actuators and controllers are wired properly, and sensor cables are routed to avoid strong electrical interference. In the commissioning phase, each valve's airflow is calibrated, and face velocity set points are set. The stability and response time of face velocity at fully open, half-open, and closed viewing window positions are tested. Multi-valve coordination and fan VFD joint commissioning are then performed to verify the emergency exhaust mode (fully open viewing window alarm). After commissioning, airflow measurement and sensors are regularly calibrated to ensure long-term reliable face velocity performance.

The exhaust airflow of a fume hood equals the face velocity multiplied by the sash opening area. The variable airflow damper acquires the sash opening degree and opening area in real time through the sash displacement sensor. The controller calculates the required exhaust airflow based on the set face velocity as the target value. Simultaneously, the actual exhaust airflow is measured in real time within the damper's measuring section. The actuator adjusts the vane opening based on the deviation between the two values, ensuring the actual airflow follows the target airflow. When the sash is opened wider or the opening area increases, the damper automatically increases airflow. When the sash is closed, airflow is automatically reduced. Therefore, regardless of the sash position, the face velocity remains within the set safe range.

Displacement control (also known as window opening control) indirectly calculates the required air volume based on the window opening, offering fast response and lower cost. However, it assumes that the face velocity is solely related to the window opening and cannot compensate for air volume changes caused by factors such as filter blockage or fan aging. Face velocity control directly installs a face velocity sensor at the window for closed-loop regulation based on actual face velocity, providing more direct and higher safety control. However, the sensor is located in the contaminated area, requiring regular cleaning and calibration. High-standard laboratories can adopt face velocity control or a combination of displacement control with air volume measurement, with the specific choice determined based on safety level and budget.

Most of the time, the sash of a fume hood is in the closed or slightly open position. The constant airflow system continuously exhausts air at maximum airflow regardless of the sash opening, often discharging air that has been conditioned by air conditioning, resulting in high energy consumption. The variable airflow system reduces the exhaust volume to a very low maintenance airflow when the sash is closed, significantly reducing the exhaust volume per hood. The VAV dampers of multiple fume hoods aggregate the airflow demand to coordinate the variable frequency drives of the exhaust and supply fans, thereby reducing the overall laboratory air conditioning and ventilation energy consumption. The more fume hoods there are and the longer the sash remains closed, the more significant the energy savings become, typically allowing the increased investment to be recovered within several years.

Venturi-type airflow measurement sections feature stable flow channels and a clear correlation between differential pressure and airflow. When paired with high-quality differential pressure sensors, measurement accuracy can meet air velocity control requirements under proper installation and regular calibration conditions. Measurement drift primarily stems from dust accumulation or leaks in the sampling tubing, sensor aging due to long-term use, or crystallization or dust contamination within the valve. In corrosive environments, corrosion-resistant valve bodies and sensors should be selected. Periodic checks of the sampling tube, cleaning of the measurement section, and calibration of zero points and ranges are essential. Ensuring valve protection during laboratory renovation phases with dust control measures can effectively prevent drift.

Safety Design Requirements VAV systems must enter a safe state during power outages or malfunctions: Valves are typically designed as fail-open or maintained at maximum exhaust capacity (fail-safe type), ensuring fume hoods continue to exhaust at maximum airflow, prioritizing energy waste over the release of hazardous gases; the monitoring panel issues audible and visual alarms to alert personnel for intervention. When selecting, clarify the actuator's de-energized position and alarm logic. Critical laboratories can be equipped with emergency exhaust buttons, which, when pressed, fully open the valves and run the fans at high speed. Regularly conduct drills for fault alarms and emergency operations to prevent fume hoods from continuing gas generation experiments with closed valves.

Each fume hood at the terminal is equipped with a variable air volume Venturi valve, a window displacement sensor (or face velocity sensor), and a control and display alarm panel; the exhaust system is equipped with a variable frequency exhaust fan, while the fresh air system is equipped with a variable frequency fresh air fan and a room pressure differential control. Multiple valves and fans are connected to the ventilation monitoring system via a controller and communication bus to achieve air volume summation, variable frequency linkage, status monitoring, and alarm logging. The system design must comprehensively consider the balance between exhaust volume and make-up air volume, laboratory negative pressure gradient, fan redundancy, and emergency power supply. Compared to constant air volume systems, VAV systems require higher equipment and commissioning requirements and should be designed and commissioned by professional laboratory ventilation engineers.

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