Fume Hood VAV Control Damper | Face Velocity Control

A fume hood VAV damper changes exhaust airflow as the hood opening or measured face velocity changes. This XICHENG product family combines a round PP butterfly damper with a fast actuator, controller inputs, airflow measurement connections and optional local operating components. It is intended for laboratory exhaust branches where the hood control sequence must respond to sash movement while maintaining the project-defined face-velocity target.

The package does not create exhaust airflow. It modulates the hood branch while the exhaust fan and duct system provide the pressure needed to move air. The control result therefore depends on the complete loop: hood opening, sensor, controller, actuator, damper, airflow pickup, fan system and field commissioning. The selected schedule must state which parts XICHENG supplies and which parts are furnished or coordinated by others.

What the Configured Package Controls

The controller converts a hood demand signal into a damper command. With sash-position control, a draw-wire or rotary position sensor indicates the open sash area and the controller raises or lowers the airflow demand accordingly. With direct face-velocity control, a hood-mounted air-velocity sensor provides the feedback used to correct the damper position. A configured system may also use measured duct airflow to verify or close the airflow loop.

The available package can place the controller and fast actuator together on the damper or use a separate controller with an external actuator. Local panel options can display face velocity, sash opening, airflow indication and operating status. Depending on the specified configuration, the panel and controller can provide audible or visual alarm functions, equipment and lighting commands, emergency exhaust, economy mode, occupancy input and Modbus RTU communication.

Choose This Product Family When

• The exhaust branch serves a laboratory fume hood or fume cupboard whose airflow demand changes with sash position.
• The project requires a PP round butterfly damper and the complete exposed assembly can be accepted for the intended exhaust stream.
• The control design uses sash-position sensing, direct face-velocity sensing or a clearly defined combination of hood and duct measurements.
• The damper must react through a fast actuator and the final response will be commissioned as part of the installed hood system.
• The schedule can define local panel functions, alarms, occupancy mode, BMS points and emergency behavior for each hood tag.

This family is especially useful when the buyer wants one supplier to coordinate the damper body, actuator and hood-control interface. It can also support projects in which a separately specified actuator or controller must be integrated, provided the signals, torque, travel time and feedback are confirmed before production.

Do Not Select It from the Product Name Alone

A fume hood VAV control damper is not the same as a generic round VAV damper. A generic unit can regulate a duct airflow setpoint without knowing the hood sash position, face velocity or alarm state. This page adds hood-specific sensing, user indication and control sequencing. For a general supply or exhaust branch, use the Round VAV Butterfly Damper or the planned Duct Airflow Control Damper.

The product is also not a Venturi air valve. Its airflow-control element is a rotating butterfly blade, even though the PP body uses differential-pressure pickup geometry to support airflow measurement. Where the specification requires a Venturi valve mechanism, evaluate the planned Fume Hood Venturi Air Valve.

Do not use this product as evidence that a fume hood has passed containment testing. Actuator movement, duct airflow and average face velocity are related but different measurements. The installed hood must be balanced, calibrated and accepted under the project test procedure.

Key Specifications, Sizes and Airflow References

Select the fume hood VAV damper from the hood airflow schedule and control method first, then check the duct connection and actuator package. The table below separates confirmed product-family facts from values that depend on the selected controller or project sequence.

Product-Family Specifications

Round PP Damper Size and Velocity-Reference Table

The airflow columns show the calculated volume at three duct velocities for each internal diameter. They help compare body sizes, but they do not define the hood operating points. Select the final size from the minimum, normal, maximum and emergency exhaust schedule together with available pressure, noise limits and the control sensor’s usable range.

The DN250 row has a lower 1 m/s reference than a simple area calculation would suggest, while its 6 m/s and 10 m/s values follow the published source table. The values are reproduced as issued rather than silently corrected. Confirm the final project airflow schedule and approved selection data before ordering.

DN250 and DN315 Mechanical Envelope

Actuator and controller clearance often determines whether a damper fits above a fume hood or within a congested exhaust riser. The drawing below shows the source-family DN250 and DN315 flange-body references with the integrated control assembly mounted to the side.

The drawing identifies approximately 330 mm flange OD and 250 mm internal diameter for DN250, and approximately 395 mm flange OD and 315 mm internal diameter for DN315. Both shown bodies use a 280 mm drawing height in this specific illustration. This differs from the longer body-length values in the general size table, so the project must use the approved configuration drawing rather than combining dimensions from separate source views. Keep access around the controller, pressure tubes, wiring and actuator release controls.

Fume Hood Control Strategies and Package Options

The correct control package is determined by the signal that represents hood demand and by where the actuator-control logic is located. The five XICHENG configurations use the same general product family but are not interchangeable model names. Select one architecture for each hood tag and list its sensor, actuator, panel and communication scope.

FHC10 Integrated Position or Face-Velocity Control

FHC10 places the controller and fast actuator on the damper. Its analog input can be configured for a resistive sash-position sensor or a voltage face-velocity sensor, while a dry contact can accept an occupancy signal. The controller can provide operating status, hood-lighting control and an analog airflow-feedback signal, and it connects to a local panel and Modbus RTU network.

The published actuator options are 5 Nm at 2.0 seconds, 15 Nm at 5.0 seconds and 30 Nm at 9.0 seconds for 0-90 degree travel. Select torque from the actual damper and shaft load, not from response time alone. The 5 Nm option is the fastest of the listed models, but a larger body or higher mechanical load may require the higher-torque configuration.

FHC11 Direct Face-Velocity Control

FHC11 uses direct face-velocity feedback and an integrated actuator/controller. The XICHENG product source lists 24 VDC power, a 0-10 or 2-10 VDC face-velocity input, local panel connection, Modbus RTU and digital outputs for status/fan coordination and hood lighting. The listed body sizes are DN250 and DN315.

This configuration is useful when a sash-position sensor is difficult to install or when the project specifically requires direct velocity feedback. Sensor placement and field calibration matter because local cross-drafts, temperature effects and hood geometry can influence the signal. The commissioning procedure must compare the controller reading with the measured average face velocity across the hood opening.

FHC11-S Sash-Position Control

FHC11-S uses a resistive position signal from the sash mechanism. As the opening changes, the controller follows the calibrated relationship between sash travel and required exhaust. This approach provides an immediate demand change when the sash moves, but it still requires airflow and face-velocity verification because the same sash position can produce different results when duct pressure or system resistance changes.

State the sash type, maximum operating opening, bypass area if applicable, sensor travel and closed/open calibration values. A vertical-sash calibration cannot be assumed for a horizontal or combination sash.

FHC12 Separate Controller with External Actuator

FHC12 separates the fume hood controller from the actuator. It accepts sash-position and face-velocity inputs, receives actuator position feedback, and sends an analog actuator command. This is the suitable architecture when the actuator must be selected separately for a specified brand, torque, travel time, shaft arrangement or replacement strategy.

The controller does not make an arbitrary actuator compatible. Confirm 24 V power, analog command and feedback ranges, torque, angular travel, rotation direction, shaft dimensions, protection class and fail response. The supplied wiring diagram and I/O schedule must match the actual actuator.

FHC100 Automatic-Sash Configuration

FHC100 adds sash open, close and inhibit functions to the airflow-control sequence. The source configuration can coordinate a sash motor, position sensor, anti-pinch input, occupancy sensor, local panel and optional foot switch. When the sash moves, the exhaust demand must change with it; when an obstruction is detected, sash motion must stop or reverse according to the approved safety sequence.

Automatic sash operation is not included in the other four packages unless it is explicitly scheduled. Projects that need a dedicated sash-drive system should also review the Automatic Fume Hood Sash Controller and define which device owns sash safety, movement and airflow commands.

How Face-Velocity Control Works

The control loop begins with a target defined by the hood risk assessment and ventilation design. The controller then uses sash position, direct face velocity or another configured input to calculate the exhaust demand. It commands the actuator to move the butterfly blade and uses the available feedback to determine whether the demanded condition has been reached.

Sash-Position Demand

A vertical sash changes the open hood area. If the target face velocity remains constant, a larger opening generally requires more exhaust and a smaller opening requires less. A draw-wire or rotary sensor reports the sash position, and the controller converts the calibrated opening into an airflow demand. Because the signal changes as soon as the sash moves, the actuator can begin repositioning without waiting for a downstream velocity change to develop.

The calculation depends on the actual sash geometry. The commissioning record should identify the fully closed point, maximum operating opening, working minimum, sash width and any bypass or permanent opening. Position control also needs a defined minimum exhaust value for a closed or nearly closed sash. It should not command zero airflow unless the hood design and safety procedure expressly permit that condition.

Direct Face-Velocity Feedback

A face-velocity sensor measures local air movement through a hood-sidewall port and returns an analog signal to the controller. When the measured value differs from the setpoint, the controller changes the damper command. This arrangement measures the controlled variable more directly, but the sensor reading can be influenced by its location, room air currents, temperature and hood geometry.

Field calibration links the sensor signal to the average velocity measured across the hood opening. One point at the sidewall is not automatically equal to the traverse average. The hood must be tested at the required sash positions, and alarm thresholds should be set only after the normal operating value is stable.

Measured Airflow and Damper Response

The PP damper body includes pressure-pickup connections that can support a configured airflow-measurement loop. The controller converts differential pressure into airflow using the applicable relationship for the selected body and then adjusts the blade when measured flow departs from demand. This feedback helps correct for changes in duct pressure, but it works only within the sensor, controller and actuator range established for the supplied package.

Response time must be described by the event being measured. The source family lists a control response of less than one second, an FHC10 5 Nm actuator travel of 2.0 seconds for 0-90 degrees, and a 2-3 second face-velocity stabilization reference. These are not three versions of the same number. The first concerns controller response, the second concerns full actuator travel, and the third concerns the installed loop approaching a stable hood condition. Field acceptance should define its measurement point and tolerance.

Components, Interfaces and Supply Boundary

A complete fume hood airflow-control package can include more than the damper shown in the product image. The quotation and valve schedule should identify every supplied component so the installer knows which devices arrive mounted, which require field mounting, and which are furnished by the controls or fume hood contractor.

Damper and Measurement Assembly

The core assembly is the round PP butterfly damper, blade, shaft, flanges or socket connection, pressure pickup and actuator mounting arrangement. A PP+GF blade with silicone covering is identified for the source family. The body material can reduce exposure of metal surfaces in corrosive exhaust applications, but tubing, seals, shaft components, fasteners, sensor connections and actuator location still require separate compatibility review.

Provide sufficient straight duct where the selected measurement method requires it and keep the pickup tubing short, supported and free from kinks, liquid traps and reversed high/low connections. The damper should remain accessible for blade inspection, sensor-zero checks and actuator service.

Controller, Panel, Sensors and BMS

The selected controller receives the hood demand and sends the damper command. Depending on configuration, inputs can include a resistive sash-position sensor, a voltage face-velocity sensor, occupancy contact, actuator feedback and airflow measurement. Outputs can include actuator command, airflow feedback, operating status and lighting control. The local panel can provide normal/alarm indication, equipment control, emergency exhaust and economy-mode functions.

Modbus RTU is available on the identified XICHENG controllers, but the project still needs a point list. Define which values are writable, which are read-only, what happens after communication loss, and whether local safety functions continue without the BMS. Network communication should supervise and coordinate the hood; it should not replace the local control loop unless the approved sequence expressly assigns that responsibility.

What the Package Does Not Replace

The package does not replace the fume hood enclosure, exhaust fan, variable-frequency drive, main duct, room supply-air system, room pressure controller or test-and-balance work. It cannot correct a hood with a blocked baffle, unsuitable sash opening, severe cross-draft or inadequate exhaust pressure merely by moving the damper faster.

It is not a fire damper, smoke damper or certified isolation device. It also does not prove containment from the damper’s airflow reading alone. Hood acceptance must evaluate the installed enclosure, room conditions and exhaust system under the test procedure specified for the project.

Applications, Configuration and RFQ Information

This laboratory fume hood VAV damper is intended for projects that need the exhaust volume to follow a changing hood opening or a measured face-velocity signal. Selection starts with the hood and control sequence, not with the nominal duct diameter.

Good-Fit Applications

The package is a good fit for vertical-sash chemical fume hoods, educational and research laboratory hoods, pharmaceutical or industrial laboratory exhaust branches, and selected walk-in or floor-mounted fume cupboards. Direct face-velocity control can be considered where a position sensor is difficult to install. Sash-position control is suitable where the sash geometry and travel can be measured and calibrated. An integrated FHC10 package suits projects that want the controller and actuator together, while FHC12 suits projects that must use a separately specified actuator.

PP construction is relevant when the exhaust stream calls for a nonmetallic damper body. Provide the chemical list, concentrations, temperature, condensate conditions and cleaning agents so the body, blade covering, shaft components, tubing and seals can be reviewed as an assembly. A broad description such as “acid exhaust” is not enough to confirm compatibility.

Conditions Requiring Another Product

Use a general Round VAV Butterfly Damper when the branch is controlled only from a duct airflow or BMS setpoint and does not require hood-specific sensing, alarms or user controls. Use the Rectangular VAV Butterfly Damper where the connection is rectangular rather than round.

Evaluate the planned Fume Hood Venturi Air Valve when the project specification requires a Venturi mechanism or an existing Venturi valve schedule must be matched. Use a dedicated fire or smoke damper where a rated life-safety device is required. If the primary requirement is automatic sash movement rather than exhaust modulation, review the automatic sash-control product family and coordinate its output with the fume hood airflow controller.

Selection Sequence

1. Define the hood type, sash arrangement, maximum working opening and required control objective.
2. List minimum, normal, maximum and emergency exhaust airflow for each hood tag.
3. Choose sash-position sensing, direct face-velocity sensing or an approved combined strategy.
4. Select the round damper size and confirm that available duct pressure supports the complete scheduled range.
5. Confirm PP compatibility for the complete exposed assembly and choose flange or socket connection.
6. Select FHC10, FHC11, FHC11-S, FHC12 or FHC100 from the required inputs and actuator architecture.
7. Define local panel functions, alarms, occupied/unoccupied mode, emergency operation and communication-loss behavior.
8. Complete the I/O list, BMS point list, wiring responsibility and field commissioning procedure.

Do not select only from maximum flow. A body that can pass the maximum air volume may produce a weak measurement signal at minimum flow, excessive noise at high velocity, or insufficient authority at the available pressure. The selected range must be checked as a complete operating envelope.

Information Required for Configuration and Quotation

For each hood, provide the tag, hood type, sash type, opening width and height, maximum working opening, bypass area if applicable, and the required face-velocity or airflow setpoints. Include minimum, normal, maximum and emergency flow, available pressure at the damper, duct diameter, connection, installation orientation and available actuator-service clearance.

For the control package, state the preferred sensing method, sash-sensor travel, face-velocity sensor requirement, actuator arrangement, power supply, analog signals, dry contacts, Modbus RTU requirements, local panel type, alarm sequence, emergency exhaust behavior, occupancy mode and fail position. For FHC100, add sash motor, anti-pinch, foot-switch and manual-release requirements.

Attach the hood elevation, exhaust duct layout, controls schematic and point list when available. XICHENG can then return a configured product schedule identifying the selected body, controller, actuator, sensors, panel, supplied accessories, drawing references and commercial quotation.

Installation, Commissioning and Acceptance

Install and commission the fume hood VAV damper as one control loop. Mechanical fit, sensor calibration, controller settings and hood performance must be checked together; completing only the duct connection or actuator wiring is not sufficient.

Before Installation

Check the approved damper drawing against the duct diameter, connection, orientation and available body length. Reserve access for the actuator, controller, pressure tubes, wiring terminals and manual controls. Support the duct independently so the PP body and flanges are not used to carry misaligned ductwork or external loads.

Mount the sash-position or face-velocity sensor in the location defined by the control design. Route signal wiring away from power cables where practical and follow the specified shielding and grounding method. Pressure tubing must connect to the correct high and low ports without sharp bends, trapped liquid or unsupported loops. Verify the power source before energizing the controller and actuator.

Commissioning Sequence

1. Inspect the hood, sash, duct, damper blade, actuator and sensor installation before applying control power.
2. Confirm rotation direction, mechanical travel and any blade or shaft limits without forcing the linkage.
3. Zero and range the airflow or pressure sensor according to the selected package.
4. Calibrate sash fully closed and maximum operating positions, or calibrate the face-velocity sensor against an accepted hood-opening traverse.
5. Enter minimum, normal, maximum, emergency and unoccupied operating values from the approved schedule.
6. Test panel indication, high/low alarms, lighting, equipment command, emergency exhaust and occupancy mode where supplied.
7. Verify analog command and feedback, dry contacts, Modbus points and communication-loss behavior.
8. Operate the sash through the required positions and measure the resulting airflow and face velocity after the loop stabilizes.
9. Complete the project containment or hood-performance test under the specified room and exhaust-system conditions.

Record the final sensor calibration, controller settings, actuator direction, flow values, alarm thresholds and BMS addresses. These records provide the baseline for future troubleshooting and prevent a replacement controller or sensor from being configured from memory.

Maintenance and Revalidation

Inspect the damper blade, shaft, pressure pickup, tubing, sensor, actuator and wiring at the interval required by the laboratory program. Clean deposits using methods compatible with the supplied materials. A blocked pickup tube or displaced face-velocity sensor can cause a control error even when the actuator still moves normally.

Recheck airflow and hood response after changes to the exhaust fan, duct system, filters, sash mechanism, sensor, controller, actuator or room supply-air arrangement. Revalidation is also appropriate when alarm frequency changes, the sash no longer moves smoothly, displayed values drift from field measurements, or the laboratory process changes.

Related Laboratory Airflow Products

Use the Round VAV Butterfly Damper for a circular branch that does not require hood-specific sash, face-velocity, panel and alarm functions. Use the Rectangular VAV Butterfly Damper where a made-to-order W x H body is required. The planned Duct Airflow Control Damper is the adjacent choice for general duct airflow or pressure control.

Where the specification requires a Venturi mechanism, evaluate the planned Fume Hood Venturi Air Valve. Where automatic sash movement is the primary equipment scope, review the Automatic Fume Hood Sash Controller and coordinate its position and safety outputs with the airflow-control sequence.

Frequently Asked Questions

Does the damper control face velocity by itself?

No. The butterfly damper changes exhaust resistance and airflow, but face-velocity control requires a sensor or calibrated sash signal, controller logic, actuator, available exhaust pressure and field commissioning. The hood enclosure and room air movement also affect the measured result.

Which sensing method should be selected?

Choose sash-position control when the sash geometry and travel can be measured reliably and the opening-to-airflow relationship can be commissioned. Choose direct face-velocity sensing when the project requires that feedback or a position sensor is impractical. A combined strategy can use fast sash demand with velocity or airflow feedback, but every input and control responsibility must be defined.

What is the difference between FHC10 and FHC12?

FHC10 integrates the controller with a fast actuator and supports a configured sash-position or face-velocity input. FHC12 is a separate controller that commands an external actuator and receives actuator feedback. Select FHC12 when actuator brand, torque, travel time, shaft interface or replacement strategy must be specified independently.

Does FHC100 automatic sash control come with every package?

No. FHC100 is the configuration that adds commanded sash movement and can coordinate a sash motor, position sensor, anti-pinch input, occupancy sensing and optional foot switch. FHC10, FHC11, FHC11-S and FHC12 do not include those automatic-sash components unless the quotation explicitly adds them.

Can actuator position be accepted as airflow?

No. Position feedback confirms the blade or actuator angle. Actual airflow changes with duct pressure, fan operation and system resistance. Use the configured airflow measurement and field balancing procedure when airflow must be verified, and use the required hood test when containment or average face velocity must be accepted.

What project data are needed for selection?

Provide the hood and sash type, sash dimensions, minimum/normal/maximum/emergency exhaust, face-velocity target, available pressure, duct diameter and connection, air-stream conditions, sensing method, actuator architecture, panel functions, power, I/O, communication, fail behavior and drawings. Add automatic-sash safety and motor information only when that configuration is required.

Contact the Xicheng Engineering Team Today

Send the fume hood schedule, sash dimensions, airflow calculations, duct layout and control schematic. Include the preferred sensor method, controller/actuator architecture, panel functions, BMS points and air-stream description. XICHENG will use these inputs to prepare a configured damper and control-package schedule, connection drawing and quotation.

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