Venturi Valve

Product Model	Venturi Constant Air Volume Valve (CAV)
Category	Laboratory Products
Reference Price	Price on request

Hot Customizable for Working Conditions 10 Technical Parameters

Product Overview

The Venturi valve, full name Venturi constant airflow valve, is a specialized valve used in laboratory ventilation systems to automatically maintain a constant exhaust airflow, abbreviated as CAV valve. The valve has a Venturi tube-shaped body with an axially movable conical valve core and a spring adjustment mechanism inside, installed on the exhaust branch duct of the fume hood. When system air pressure fluctuates due to the opening or closing of other fume hoods, variable-frequency fan operation, or filter clogging, the valve core automatically moves under the combined action of pressure differential and spring force to change the flow area, keeping the airflow through the valve at the set value without requiring power or control signals.

With an ordinary damper, once the opening angle is fixed, the airflow changes with duct network pressure variations. In a parallel system with multiple fume hoods, switching some hoods on or off causes airflow fluctuations in the remaining hoods, and face velocity cannot be guaranteed. The Venturi valve relies on mechanical self-powered regulation to lock the exhaust airflow of each fume hood at the set value. Once the system airflow balance is commissioned, it remains stable long-term, unaffected by the switching of other terminals, significantly improving fume hood safety and avoiding frequent adjustments. The valve body is integrally molded and available in ABS, stainless steel, and aluminum alloy; the corrosion-resistant type withstands acid and alkali gases.

The Venturi constant airflow valve supplied by Xicheng Environmental Protection features an integrally molded, compact valve body with corrosion resistance and acid/alkali resistance. The valve is equipped with an airflow setting mechanism that can be set on-site according to the design exhaust airflow of the fume hood, and its circular interface connects to the duct. It is suitable for constant airflow fume hood exhaust systems in chemical laboratories, testing institutions, and semiconductor plants. For applications requiring dynamic adjustment with sash opening, the variable airflow Venturi valve is recommended.

Working Principle

The Venturi valve achieves constant airflow through the Venturi throttling effect and the force balance principle. Inside the valve, an annular throttling passage is formed between the conical valve core and the valve body. One side of the valve core is subjected to spring thrust, while the other side is subjected to the aerodynamic force generated by the pressure differential across the valve. When the pressure differential increases, the aerodynamic force pushes the valve core toward closing, reducing the annular passage area and increasing resistance, which offsets the effect of the increased pressure differential. When the pressure differential decreases, the spring pushes the valve core toward opening, enlarging the passage area. The valve core reaches force balance at a new position, keeping the airflow through the valve essentially constant within a certain pressure differential range.

This regulation is accomplished entirely by the mechanical force balance between the valve core and the spring, requiring no external power, sensors, or controllers, resulting in high reliability and fast response. It is a self-powered constant airflow device. The Venturi-shaped flow passage of the valve body accelerates the airflow and forms a stable pressure differential characteristic, establishing a definite correspondence between valve core position and airflow. Rotating the setting mechanism to change the spring preload allows different constant airflow values to be set. The corrosion-resistant valve body and valve core do not rust or jam even after long-term exposure to acid and alkali laboratory exhaust, ensuring the mechanical mechanism remains flexible in corrosive environments.

Structural Composition

The Venturi valve consists of a valve body, a conical valve core, a valve core guide rod, a spring assembly, an airflow setting mechanism, and connections at both ends. The valve body is a Venturi-shaped cylinder, integrally molded, with the inner wall profile designed according to the Venturi flow passage. The circular connections at both ends join the duct via socket or flange connections. The conical valve core is located at the center of the valve body and can move axially along the guide rod, forming an annular airflow passage between the valve core and the valve body.

The rear of the valve core connects to the spring and adjustment mechanism; the spring force acts opposite to the aerodynamic force and remains in balance. The exterior of the valve body features an airflow scale and a setting knob or locking mechanism. During commissioning, the valve is set to the design exhaust airflow of the fume hood and then locked. A limit stop structure can be provided inside the valve to restrict the valve core stroke, ensuring effective regulation within the working pressure differential range. For the corrosion-resistant type, the valve body and valve core are made of ABS, stainless steel, or aluminum alloy with anti-corrosion treatment, featuring few moving parts and low maintenance. The installation direction follows the airflow direction marking on the valve body; horizontal or vertical installation is determined according to model requirements.

Specifications and Models Table

The table below compares the Venturi constant airflow valve with the ordinary damper. Selection is determined by the terminal control method.

Item	Venturi Constant Airflow Valve	Ordinary Damper
Airflow Control	Automatically constant despite pressure differential fluctuations	Fixed opening; airflow varies with pressure
Power & Control	No power required	Manual / Electric
Application	Constant airflow fume hoods	General airflow balancing
Commissioning	Set once, stable long-term	Affected by terminal switching

Product Features

The Venturi valve is mechanically self-powered, maintains constant airflow, and requires no power, making it a reliable terminal device for constant airflow fume hood exhaust in laboratories. Its main features are as follows.

Venturi effect combined with spring force balance keeps airflow constant despite pressure differential fluctuations
Purely mechanical self-powered regulation, no power, sensors, or controllers required
Set once during commissioning, unaffected by the switching of other terminals
Integrally molded valve body, compact structure, few moving parts
ABS, stainless steel, or aluminum alloy construction, corrosion-resistant and acid/alkali resistant
Equipped with airflow scale setting mechanism for convenient on-site setting
Fast response, reliable operation, low maintenance

Body Material	ABS / Stainless Steel / Aluminum Alloy
Molding Process	One-piece housing
Control Method	Mechanical Self-Adjusting Volume Control
Power Requirements	No power required
Measurement Principle	Venturi Throttling Effect
Adjustment Components	Conical Valve Core with Spring
Corrosion resistance performance	Anti-corrosion, Acid and Alkali Resistant
Setting Method	Body Scale Setting Lock
Connection method	Round Spigot / Flange
Applicable Systems	Variable Air Volume Fume Hood Exhaust

Application Industries

Chemical laboratory variable air volume fume hood exhaust control
Examination institutions and third-party laboratory fume hood terminals
Pharmaceutical companies QC laboratory variable air volume exhaust system
Semiconductor and panel factories wet etching area variable air volume exhaust
Schools and research institutions chemical laboratory fume hoods
Variable air volume exhaust control for multiple fume hoods in parallel
Hospital pathology and clinical laboratory variable air volume fume hoods

Typical Process Locations

The Venturi valve is installed on the exhaust branch pipe of each variable air volume fume hood, typically located between the cabinet top exhaust port and the horizontal main pipe or on the branch pipe before entering the vertical shaft. The valve body connects to circular ducts at both ends. Each fume hood is equipped with one variable air volume valve to lock the exhaust volume at the design value. The fume hoods are paralleled into the exhaust main pipe and centralized fan. When one hood is shut down, the branch pipe is closed, and the valves of the remaining hoods automatically adapt to pressure changes to maintain airflow. Sufficient space should be left for scale setting and maintenance, and airflow direction should be installed according to the valve body markings.

During system commissioning, the fan is turned on and the system operates under design conditions. Each Venturi valve is set to the fume hood's rated exhaust volume, and the window face velocity is verified using an anemometer or flow hood, then the setting mechanism is locked. Afterward, the system automatically maintains the airflow under various terminal switch combinations. Variable air volume Venturi valves are suitable for fume hoods with fixed or preset window openings. If constant face velocity is required at any window opening while achieving energy savings, variable air volume Venturi valves should be used.

It relies on mechanical force balance for automatic adjustment. The conical valve core inside the valve is simultaneously subjected to spring force and aerodynamic force generated by the pressure differential between the valve front and rear, where the aerodynamic force pushes the valve core to close the passage and increase resistance when the pressure differential rises, and the spring opens the valve core when the pressure differential falls; the valve core moves to a force-balanced position, maintaining airflow constant within the design pressure differential range. The entire process does not require power supply, sensors, or control algorithms, hence it is called a self-powered constant airflow valve, with high reliability, making it particularly suitable for laboratory exhaust systems where electrical control complexity is to be avoided.

It is not absolutely constant but maintains airflow within an allowable deviation range under specified working differential pressure. Venturi valves have applicable upper and lower limits of differential pressure: when the differential pressure is below the lower limit, the spring pushes the valve core to its maximum opening but still fails to maintain airflow; when the differential pressure exceeds the upper limit, the valve core closes to its minimum position but cannot fully compensate, and airflow will still vary outside the working range. When selecting, ensure that the differential pressure across the valve before and after normal system operation falls within the working range. Consider pressure changes caused by fan frequency variation and filter blockage, and have the design personnel verify if necessary.

Ventilation hoods with fixed sash openings and constant airflow rates are suitable for mechanical Venturi variable air volume (VAV) dampers, which offer low initial investment, no power supply requirement, and simple maintenance. For hoods requiring constant face velocity during sash sliding and reduced airflow when the sash is closed to save air conditioning fresh air energy consumption, variable airflow Venturi dampers are recommended. These dampers are equipped with actuators and controllers to dynamically adjust airflow based on sash displacement or face velocity signals. Modern laboratories with multiple hoods, long operating hours, and high energy savings requirements often use VAV systems. Budget constraints or limited cabinet space may make fixed airflow dampers a more suitable option.

Venturi valves commonly use materials such as ABS engineering plastic, stainless steel, and aluminum alloy. ABS valve bodies are molded as one piece, rust-resistant, and exhibit good corrosion resistance to general acid and alkali ventilation, with low cost, making them a common choice for laboratory fume hood ventilation; stainless steel or corrosion-treated valve bodies can be selected for highly corrosive environments, with the specific material determined based on the composition and concentration of the ventilation. Aluminum alloy valve bodies are lightweight, but their corrosion resistance depends on surface treatment. When selecting, specify the common reagents and ventilation properties of the fume hood to the manufacturer, and verify the corrosion resistance table of the material if necessary, to avoid corrosion and jamming of moving parts such as valve cores and springs.

When multiple fume hoods share a fan and main duct, switching or adjusting certain fume hoods can alter the network resistance, causing pressure fluctuations in the main duct. If each fume hood only uses a standard fixed damper, the airflow of the operating fume hoods will fluctuate unpredictably, potentially falling below safe face velocity levels. After installing Venturi variable air volume (VAV) dampers on each fume hood, the dampers automatically adapt to changes in main duct pressure, locking the airflow of each fume hood to the set value without interference. The system only requires a single initial setup during commissioning, ensuring stable operation and reducing the need for repeated airflow balancing adjustments. This is the core value of variable air volume dampers in parallel fume hood systems.

During installation, ensure the valve body's airflow direction indicator aligns with the actual airflow. Both ends of the valve should be sealed. Maintain a certain length of straight pipe sections before and after the valve to avoid proximity to elbows or diameter changes that could affect airflow stability. Leave sufficient operating space on the scale side of the valve body for maintenance. For maintenance, regularly inspect whether the valve core is flexible, check for dust accumulation or crystallization causing jamming, and verify if the spring and setting mechanism are loose. In corrosive environments, inspect the valve body and moving parts for corrosion. During laboratory renovation and cleaning stages with significant dust, provide temporary protection for the valves to prevent cement dust from entering and affecting the valve core's movement. Before operation, individually verify the air volume setting for each valve.

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