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 Variable Air Volume (VAV) Damper, also known as the Venturi Constant Airflow Damper, is a specialized valve used in laboratory ventilation systems to automatically maintain a constant exhaust airflow. It is commonly referred to as a CAV Damper. The valve has a Venturi tube-like appearance and is equipped with an axially movable conical valve core and a spring adjustment mechanism, installed on the exhaust branch pipe of a fume hood. When the system pressure fluctuates due to other ventilation柜 openings, variable frequency fans, or clogged filters, the valve core automatically moves under the action of pressure difference and spring force to change the flow area, ensuring the airflow through the valve remains at the set value without requiring power or control signals.

With conventional dampers, once the opening is fixed, the airflow changes with network pressure variations. In multi-fume hood parallel systems, opening or closing certain units can cause airflow fluctuations in others, making it difficult to maintain consistent face velocity. Venturi Dampers rely on mechanical self-regulation to lock the exhaust airflow of each fume hood at the set value. After a one-time system airflow balancing adjustment, the system remains stable long-term, unaffected by other terminal openings, significantly enhancing fume hood safety and eliminating the need for frequent adjustments. The valve body is molded as a single unit, available in materials such as ABS, stainless steel, and aluminum alloy, with corrosion-resistant versions capable of withstanding acidic and alkaline gases.

The Venturi Constant Airflow Dampers supplied by Xicheng Environmental are molded as a single unit, compact in structure, corrosion-resistant, and acid/alkali-resistant. They feature an airflow setting mechanism on the valve for on-site setting based on the fume hood's designed exhaust airflow. The circular interface connects to ductwork and is suitable for constant airflow ventilation systems in chemical laboratories, testing institutions, and semiconductor manufacturing facilities. For applications requiring dynamic airflow adjustment with sash openings, Variable Air Volume Venturi Dampers should be selected.

Working Principle

The Venturi Damper achieves constant airflow using the Venturi throttling effect and force balance principles. The conical valve core forms a annular throttling passage between the valve core and the valve body. One side of the valve core is subjected to spring thrust, while the other side is affected by the aerodynamic force generated by the pressure difference between the valve front and rear. When the pressure difference increases, the aerodynamic force pushes the valve core to move in the direction of closing, reducing the annular passage area and increasing resistance, thereby counteracting the pressure rise. When the pressure difference decreases, the spring pushes the valve core to open, increasing the passage area. The valve core reaches a new position of force balance, maintaining the airflow through the valve relatively constant within a certain pressure difference range.

This regulation is entirely mechanical, achieved through the balance of the valve core and spring forces, eliminating the need for external power, sensors, or controllers, thus ensuring high reliability and fast response. It is classified as a self-powered constant airflow device. The Venturi-shaped flow channel in the valve body accelerates airflow and forms a stable pressure difference characteristic. The valve core position has a definite correspondence with airflow, and adjusting the setting mechanism changes the spring pre-tension to set different constant airflow values. The corrosion-resistant valve body and valve core do not rust or jam when long-term exposed to laboratory acidic and alkaline exhaust, ensuring smooth movement of the mechanical mechanism in corrosive environments.

Structural Components

The Venturi Damper consists of a valve body, conical valve core, valve core guide rod, spring assembly, airflow setting mechanism, and two end interfaces. The valve body is a Venturi-shaped cylinder, molded as a single unit with an inner wall profile designed according to the Venturi flow channel. The two circular interfaces connect to ductwork via slip-fit or flange connections. The conical valve core is located at the center of the valve body and moves axially along the guide rod, forming a annular airflow passage between the valve core and the valve body.

The rear of the valve core is connected to the spring and adjustment mechanism, where the spring force counteracts the aerodynamic force and maintains balance. The valve body exterior features airflow markings and a setting knob or locking mechanism. During commissioning, the valve is set to the designed exhaust airflow of the fume hood and locked. The valve may include a limit structure to restrict the valve core travel, ensuring effective regulation within the working pressure difference range. Corrosion-resistant valve bodies and valve cores are treated with ABS, stainless steel, or aluminum alloy for corrosion resistance. With few moving parts, maintenance is minimal. Installation direction follows valve body airflow indicators, with horizontal or vertical installation determined based on model requirements.

Specification and Model Table

The table below compares the Venturi Constant Airflow Damper with conventional dampers. Selection should be based on terminal control methods.

Item	Venturi Constant Airflow Damper	Conventional Damper
Flow Control	Automatically constant under pressure difference fluctuations	Fixed opening, flow varies with pressure
Power Control	Power-free	Manual / Electric
Application	Constant airflow fume hoods	General airflow balancing
Commissioning	One-time setting, long-term stable	Affected by terminal openings

Product Features

The Venturi Damper is mechanically self-powered, maintains constant airflow, and requires no power, making it a reliable terminal device for laboratory constant airflow ventilation systems. Key features include:

Combines Venturi effect with spring force balance to maintain constant airflow under pressure difference fluctuations
Pure mechanical self-regulation, no power, sensors, or controllers required
One-time setting for long-term stability, unaffected by other terminal openings
Molded valve body, compact structure, few moving parts
ABS, stainless steel, or aluminum alloy material, corrosion-resistant, acid/alkali-resistant
Includes airflow marking and setting mechanism for convenient on-site adjustment
Fast response, reliable operation, low maintenance requirements

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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