1. Basic Logic of Laboratory Pressure Control
Laboratories with contamination risks usually operate under negative pressure, allowing air to flow into the laboratory from relatively clean areas such as corridors. The basic relationship is:
Total Exhaust Airflow > Supply Airflow
A specific airflow difference, known as Offset Airflow, is maintained between the two. The controller adjusts the supply-air and exhaust-air valves according to real-time airflow data to keep the room pressure differential within the design range.
The logic for a positive-pressure clean laboratory is the opposite:
Supply Airflow > Total Exhaust Airflow
The specific pressure differential and airflow offset should not be based on a fixed value. They should be calculated according to room airtightness, door-gap area, air-change rate, risk level, and project specifications.
2. How Should the Supply-Air System Be Configured?
A Supply Venturi Valve is usually installed on the supply-air side to control the airflow entering the room. The valve may operate in constant-air-volume or variable-air-volume mode:
Constant airflow is suitable for laboratories with relatively stable loads;
Variable airflow is suitable for projects with multiple fume hoods and frequently changing operating conditions;
Supply airflow must also satisfy outdoor-air requirements for occupants, temperature and humidity control, and minimum air-change requirements.
The maximum airflow of the supply valve should not be selected only according to current demand. Fume hood operation, future equipment expansion, and system adjustment margins should also be considered.
However, an oversized valve may cause the normal airflow to remain near the lower end of its control range, reducing control stability.
3. How Should the Exhaust System Be Configured?
Laboratory exhaust is generally divided into:
Fume Hood Exhaust: Dedicated exhaust for fume hoods;
General Exhaust: General room exhaust;
Equipment Exhaust: Exhaust for biosafety cabinets or process equipment.
When a fume hood uses variable-air-volume control, its exhaust valve must rapidly adjust the airflow according to the sash height or face-velocity signal. The general room exhaust valve provides supplementary exhaust and maintains the minimum air-change rate.
When corrosive gases are involved, ABS, coated aluminum alloy, or other corrosion-resistant structures should be selected according to the medium. The material compatibility of seals, actuators, and fasteners should also be confirmed.
4. How Is Room Pressure Controlled?
Common control methods include airflow-offset control, direct differential-pressure control, and combined control.
Airflow-Offset Control
The controller calculates the Offset Airflow from the supply airflow and total exhaust airflow. This method responds quickly and is suitable for rooms with relatively stable airtightness.
Direct Differential-Pressure Control
A Room Pressure Sensor measures the pressure differential between the laboratory and corridor and adjusts the supply or exhaust airflow accordingly. It reflects the actual room pressure, but opening and closing doors may cause temporary fluctuations.
Combined Control
The airflow offset provides the basis for rapid control, while the differential-pressure signal provides slower correction. This approach balances response speed and long-term stability and is suitable for laboratories with demanding control requirements.
During system commissioning, an appropriate deadband and time delay should be configured to prevent frequent valve oscillation caused by personnel opening doors.
Figure 3: Offset Airflow and Room Pressure Control
5. What Parameters Should Be Confirmed Before Procurement?
| Parameter | Selection Focus |
|---|---|
| Airflow Range | Minimum, normal, and maximum airflow |
| Pressure Range | Available system differential-pressure range |
| Control Accuracy | Airflow and room pressure requirements |
| Response Time | Fume hood and room control speed |
| Control Mode | CAV, VAV, or pressure control |
| Signal | 0–10V, Modbus, or BACnet |
| Fail-safe Position | Valve position during power failure |
| Material | Medium, temperature, and corrosion-resistance requirements |
| Noise Level | Allowable laboratory noise level |
The duct dimensions, number of fume hoods, room airtightness, exhaust-equipment interlocking logic, and BMS interface requirements should also be provided.
6. How Should Different Engineering Applications Be Configured?
A general chemical laboratory can use the following configuration:
Supply-Air Valve + Fume Hood Exhaust Valve + General Exhaust Valve + Room Controller
Clean laboratories should also include differential-pressure monitoring and alarms.
When multiple fume hoods share one exhaust system, the individual valves, variable-frequency fan, and static-pressure control must be coordinated to prevent the operation of one fume hood from affecting other terminals.
7. Frequently Asked Procurement Questions
Is It Sufficient to Install Only a Differential-Pressure Sensor?
No. A differential-pressure sensor only measures the result. Adjustable supply and exhaust equipment is still required to perform the control action. High-requirement projects should monitor both airflow and differential pressure.
Can a Venturi Valve Directly Replace a Room Controller?
No. A Venturi Valve measures and regulates airflow, while the room controller calculates the supply/exhaust relationship and manages pressure-control logic, alarms, and interlocks.
Is a Larger Supply/Exhaust Airflow Offset Safer?
No. An excessive airflow offset may make doors difficult to open and increase noise and energy consumption. The airflow offset should be determined according to the leakage area and target room pressure differential.
8. Yueboyang Laboratory Venturi Valve Solutions
Jiangsu Yueboyang Purification Equipment can configure supply-air and exhaust-air Venturi Valves, actuators, and control systems according to the laboratory airflow schedule, room pressure differential, number of fume hoods, and control interfaces.
Customization is available for valve body materials, airflow ranges, and BMS communication methods.
Purchasers are advised to provide a complete Room Data Sheet and Control Sequence so that valve selection, control-logic matching, and system commissioning can be completed together.
