1. How Does a Venturi Valve Achieve Pressure-Independent Control?
A Venturi Valve contains a conical valve core, a Venturi airflow passage, and a spring compensation mechanism. As air passes through the converging section, its velocity increases and static pressure decreases. The valve core automatically changes the effective free area according to the differential pressure across the valve.
The basic relationship is:
Q = C × A × √ΔP
Where Q is airflow, A is effective free area, and ΔP is the differential pressure across the valve. When the system differential pressure increases, the valve core reduces the free area. When the differential pressure decreases, the spring mechanism increases the free area, keeping the airflow relatively stable.
However, this control function is only effective within the differential pressure range specified by the manufacturer. If the actual differential pressure is below the minimum operating pressure, the valve may not achieve the design airflow even when fully open.
2. How Is the Airflow Range Determined?
The airflow range of a Venturi Valve depends on the valve diameter, valve core design, control method, and manufacturer’s calibration data. The valve should not be selected based only on the duct diameter.
| Parameter | Selection Requirement |
|---|---|
| Minimum Airflow | Meet night-mode or minimum air-change requirements |
| Maximum Airflow | Meet fully open fume hood or maximum exhaust requirements |
| Turndown Ratio | Confirm whether one valve can cover all operating conditions |
| Minimum Operating Differential Pressure | Ensure normal control at the most unfavorable point |
| Maximum Allowable Differential Pressure | Control noise, energy consumption, and component load |
| Control Accuracy and Response Time | Meet room pressure differential and rapid adjustment requirements |
If the design airflow exceeds the maximum capacity of one valve, parallel valve assemblies can be used. If the valve operates near its minimum airflow for long periods, its low-airflow control accuracy should be verified.
3. What Are the Limitations of Pressure-Independent Control?
The following conditions may still cause airflow deviations:
Insufficient differential pressure: Insufficient fan static pressure, excessive duct resistance, or an excessively distant terminal location;
Airflow outside the calibrated range: An undersized valve or an increase in exhaust demand after installation;
Improper installation: Elbows, transitions, or fan outlets located too close to the valve may create airflow swirl;
Corrosion or contamination: Acidic or alkaline gases, solvents, and particles may affect the valve core, seals, and actuator.
During procurement, the required straight-duct lengths, installation direction, maintenance space, and corrosion resistance of the valve body and sealing materials should be confirmed.
4. How to Choose Between Constant-Air-Volume and Variable-Air-Volume Models?
A constant-air-volume model maintains fixed airflow through mechanical compensation and is suitable for areas with stable air-change requirements. A variable-air-volume model is equipped with an actuator and can adjust airflow according to the fume hood sash position, room pressure, or BMS commands.
Laboratories usually require coordinated control of supply-air and exhaust-air valves. A reasonable airflow offset should be maintained to keep the room under negative pressure. Biosafety laboratories, animal rooms, and similar projects should also use differential pressure sensors to form a closed-loop control system.
Common control signals include 0–10V, 2–10V, and digital communication protocols.
5. What Information Should Be Provided for Procurement?
When requesting a quotation, it is recommended to provide:
Application: supply air, exhaust air, or fume hood exhaust;
Minimum, normal, and maximum design airflow;
Duct dimensions, valve diameter, and installation space;
Minimum and maximum available static pressure;
Constant-air-volume or variable-air-volume requirements;
Control signal, feedback signal, and communication protocol;
Noise, accuracy, and response-time requirements;
Medium, temperature, humidity, and corrosiveness;
Requirements for corrosion-resistant coatings, insulation, or special actuators.
Providing only the valve diameter is insufficient to determine whether the product can cover the actual airflow range and operate under the minimum differential pressure condition.
6. Frequently Asked Questions
Is a Venturi Valve Completely Unaffected by Pressure?
No. It can only compensate for pressure changes within its specified differential pressure and calibrated airflow ranges.
Is an Airflow Sensor Still Required?
A mechanical constant-air-volume model can stabilize airflow through its valve core and spring mechanism. A variable-air-volume system usually also requires an actuator, controller, or feedback device.
Is a Larger Valve Always Better?
No. An oversized valve may operate in the low-airflow range for long periods, reducing control accuracy and increasing installation costs.
7. Yueboyang Venturi Valve Solutions
Jiangsu Yueboyang Purification Equipment provides Venturi Valve selection and system configuration support based on the airflow, duct-system pressure differential, control signal, and corrosive environment of laboratories, hospitals, cleanrooms, and industrial ventilation projects.
Selection should verify the valve diameter, minimum operating differential pressure, airflow range, corrosion-resistance requirements, and supply/exhaust air interlocking logic. This helps reduce insufficient airflow, excessive noise, and control-interface compatibility problems.
