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Selecting the proper electric damper actuator is one of the most important decisions in any ventilation or HVAC installation. The actuator determines how reliably a damper opens and closes, how precisely air volume can be adjusted, and how long the overall system will operate without performance loss.

In commercial buildings, industrial plants, cleanrooms, and ventilation systems that operate day and night, the difference between choosing an ON/OFF actuator and a modulating actuator is significant. Both types serve different functional goals, and understanding these differences helps engineers, integrators, and equipment buyers avoid performance issues later in the project.

This article provides a practical, engineering-focused explanation of how ON/OFF actuators work, how modulating actuators work, and how to select the right option depending on your air system design. We also reference real applications and component structures to make the selection process clearer.

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1. What an Electric Damper Actuator Actually Does

A damper actuator converts electrical energy into the mechanical torque required to operate a damper blade. In ventilation projects, the actuator must:

• Deliver enough torque to move the damper reliably

• Maintain the damper position with stability

• Respond correctly to the control signal (ON/OFF or 0–10V/2–10V/Modbus)

• Operate under the site’s environmental and electrical requirements

• Maintain consistent performance for years of continuous service

While damper actuators vary in torque, control logic, return mechanism, and construction, they generally fall into two categories:

• ON/OFF (two-position) electric damper actuators

• Modulating (proportional control) electric damper actuators

Both types can appear similar on the surface, but their internal control boards and operational logic differ substantially.

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2. Understanding ON/OFF Electric Damper Actuators

ON/OFF actuators, also known as two-position actuators, move the damper to either fully open or fully closed. They are driven by a simple control signal—typically AC/DC 24V, AC 220V, or direct relay output from HVAC controllers.

A good example of this category is the 10N·m On/Off Electric Actuator commonly used for small and medium-sized dampers. 

2.1 Key Features

• Two-position control

• Fast and straightforward operation

• Mechanical simplicity

• Lower chances of misconfiguration

• Suitable for dampers that do not need fine adjustment

2.2 Ideal Use Cases

ON/OFF actuators are preferred in systems where airflow is either needed or not needed. Typical applications include:

• Kitchen exhaust and make-up air dampers

• Fresh air intake systems

• Emergency supply air dampers

• Fire/smoke system integration (non-modulating parts)

• Zones with fixed air volume requirements (CAV systems)

• Industrial exhaust where dampers operate in open/closed cycles

2.3 Advantages

• Simpler wiring

• Lower control system cost

• Fewer potential maintenance issues

• Suitable for rapid open/close requirements

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3. Understanding Modulating (Proportional) Electric Damper Actuators

Modulating actuators allow the damper to move to any position between 0% and 100%. These actuators respond to analog signals such as:

• 0–10V

• 2–10V

• 4–20mA

• Modbus RS485 (on certain models)

Engineers often use modulating actuators when ventilation airflow needs to adjust continuously to meet system demands.

3.1 Key Features

• Proportional position control

• Smooth airflow regulation

• Compatible with advanced building automation systems (BAS/BMS)

• Required for variable air volume applications (VAV)

3.2 Ideal Use Cases

Modulating actuators are essential where pressure balance and airflow precision matter. Common applications include:

• VAV boxes

• Air handling units (AHUs)

• Laboratory ventilation

• Cleanrooms

• Multi-zone climate control

• Heat recovery systems

• Industrial process ventilation

3.3 Advantages

• Precise airflow control

• Improved energy efficiency

• Higher comfort levels in commercial buildings

• Reduced system noise due to smooth damper movements

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4. ON/OFF vs Modulating: How to Decide for Your Ventilation Project

The right actuator depends on the operational requirement of the specific ventilation zone. Below is a clear comparison based on real-world engineering experience.

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4.1 Control Logic Requirements

• Choose ON/OFF if your system only needs open/close operations.

• Choose Modulating if you need adjustable airflow or pressure balancing.

Rule of thumb:
If your ventilation system communicates with a central BAS/BMS using analog or digital proportional control, you need modulating actuators.

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4.2 Airflow Precision

• ON/OFF → coarse control, used in exhaust/Supply-only systems

• Modulating → precise control, required for comfort and cleanroom systems

If airflow precision affects safety (lab fume hoods, medical areas), always select modulating actuators.

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4.3 Energy Consumption

Modulating actuators support dynamic airflow regulation, which reduces fan speed and energy consumption in well-designed systems.

• ON/OFF → suitable for fixed air volume

• Modulating → essential for VAV energy-saving strategies

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4.4 System Integration

• ON/OFF actuators can be controlled by relays, fire panels, or simple thermostats.

• Modulating actuators require a controller capable of outputting 0–10V or similar signals.

If your project uses modern building automation, modulating actuators align better with system requirements.

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4.5 Maintenance & Service

ON/OFF actuators have fewer components and are generally easier to maintain. Modulating actuators require proper signal calibration but operate more smoothly over time.

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5. Why Torque Matters (Example: 10 N·m Actuators)

Torque directly determines whether a damper can operate reliably under pressure. For small and medium dampers, 10 N·m torque is a common specification used in:

• Office space ventilation

• Retail stores

• Warehouses

• Small AHU dampers

• Light industrial exhaust systems

Higher torque models (20 N·m / 30 N·m / 40 N·m and above) are needed for:

• High-pressure ducts

• Large-area dampers

• Outdoor dampers exposed to wind load

• Heavy industrial applications

Therefore, torque selection must be based on:

• Damper blade size

• Air pressure within the duct

• Mechanical friction

• Operating frequency

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6. Importance of Feedback Options

Some ON/OFF actuators include feedback functions such as:

• Passive feedback

• Potentiometer feedback

• Integrated position signal

Feedback is important for monitoring damper position in fire systems, smoke control ducts, and cleanroom applications.

For example, the referenced 10 N·m actuator supports multiple feedback configurations suitable for different control architectures:

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7. Practical Guidelines for Selecting Actuators

A reliable selection process should consider the following engineering criteria:

7.1 Define the control signal requirement

• Relay contacts → ON/OFF

• 0–10V or 4–20mA → Modulating

7.2 Determine torque requirements

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Jiangsu Kelibo Automation Equipment Co., Ltd.

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