How are electric actuators for butterfly valves classified, and how does one select the appropriate actuator? In this article, we will address these questions by examining the subject from various perspectives—specifically: control mode, structural form, protection suitability, installation methods, and more.
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Classification by Control Mode (Most Common)
1.1 On/Off Type Electric Actuator
Features:
- Only two states: Fully Open / Fully Closed
- Simple control signals (e.g., discrete/switching signals)
- Low cost, simple structure
Applicable Scenarios:
- Water supply and drainage systems
- Fire protection systems
- General industrial piping
Note: Functions solely to “open or close”; does not regulate flow rate.
1.2 Modulating Type Electric Actuator
Features:
- Capable of achieving any opening position (0–100%)
- Accepts analog signals (e.g., 4–20mA / 0–10V)
- Built-in positioner (or control module)
Applicable Scenarios:
- Chemical process control
- HVAC systems
- Precise flow regulation
Note: Capable of both switching (On/Off) and precise flow regulation.
1.3 Intelligent Type (Smart Actuator) Electric Actuator
Features:
- Equipped with a digital control system (similar to a mini-PLC)
- Supports fieldbus communication (Modbus, Profibus, etc.)
- Enables remote monitoring, fault diagnostics, and self-calibration
Applicable Scenarios:
- Automated manufacturing plants
- Smart water treatment plants
- Petrochemical systems
Note: An actuator with a built-in “brain,” ideal for automated systems. 2. Classification by Structural Type
2. Classification by Structural Form
2.1. Quarter-turn Electric Actuators
Features:
- Output rotation angle is typically 0–90°
- Specifically designed for butterfly valves and ball valves
2.2. Partial-turn Actuators with Gearboxes (with Worm Gears)
Features:
- Built-in worm gear reduction mechanism
- High output torque
- Suitable for large-diameter butterfly valves (DN300+) and high-pressure operating conditions
2.3. Multi-turn Electric Actuators
The output involves multiple full rotations. Since this type is not applicable to butterfly valves, it will not be elaborated upon here; if you wish to learn more details, please contact us directly to request technical materials.
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Classification by Protection and Environmental Suitability
3.1. Water Protection Rating for Electric Actuator: IP Code
3.1.1. Meaning of IP: Ingress Protection (Protection Rating)
First Digit (0–6): Dust Protection Rating (Protection against solid foreign objects)
Second Digit (0–8/9K): Water Protection Rating (Protection against liquid ingress)
The higher the number, the stronger the protection capability.
3.1.2. Detailed Explanation of IP65/IP67/IP68
– Dust Protection Rating: Level 6 — Completely prevents the ingress of dust.
– Water Protection Rating: Level 5 — Protects against low-pressure water jets from any direction; no harmful water ingress.
– Water Protection Rating: Level 7 — Protects against short-term immersion; when submerged under standard temperature and pressure conditions, no water enters the interior.
– Water Protection Rating: Level 8 — Suitable for continuous operation while submerged in water (requires prior customization; lead time may be longer).
3.2. Explosion-proof Type
Used in flammable and explosive environments.
Complies with explosion-proof certification standards (e.g., the “Ex d” flameproof type, which is used in 90% of electric actuators).
3.2.1. Meaning of “Ex”:
The internationally recognized symbol for explosion protection, indicating compliance with explosion-proof standards.
Complete Marking Format (for gaseous environments):
Ex + Protection Type + Equipment Category + Temperature Class + EPL (Equipment Protection Level)
3.2.2. Section-by-Section Explanation
3.2.2.1. Protection Type
– Protection Level: Type “d” (Flameproof Enclosure — Ex d)
Principle: Robust, pressure-resistant enclosure; internal explosions are contained and do not propagate to the exterior.
Applications: Electric motors, switches, high-power actuators (most common application).
– Explosion Protection Type: Type ‘e’ (Increased Safety — Ex e)
Principle: Enhanced insulation, temperature control, and spark-free design.
Applications: Components without arcing parts (e.g., junction boxes, terminals).
– Explosion Protection Type: Type ‘i’ (Intrinsic Safety — Ex ia/ib)
Principle: Limits circuit energy; sparks/heat generated are insufficient to cause ignition.
Applications: Low-voltage circuits, sensors, small-signal control systems.
3.2.2.2 Categories
Category II: Industrial Gases (Non-mining environments)
– Gas Group IIA: Propane, Methane (Typical oil & gas applications).
– Gas Group IIB: Ethylene, Solvent Vapors (Common in chemical industries).
– Gas Group IIC: Hydrogen, Acetylene, Carbon Disulfide (Most hazardous; highest safety requirements).
Category III: Dust Environments
– Dust Group IIIA: Flyings/Lint.
– Dust Group IIIB: Non-conductive dusts.
– Dust Group IIIC: Conductive metal dusts (Most stringent requirements).
3.2.2.3 Temperature Classes T1–T6 (Maximum Surface Temperature)
Must be *lower* than the ignition temperature of the surrounding gas/atmosphere.
T1: 450°C
T2: 300°C
T3: 200°C
T4: 135°C (Most common for electric actuators/heads).
T5: 100°C
T6: 85°C (Safest; highest safety requirements).
3.2.2.4 EPL (Equipment Protection Level) — Gb / Ga
Ga: Very High Protection; suitable for Zone 0 (Continuous/long-term explosive atmosphere).
Gb: High Protection; suitable for Zone 1 (Occasional explosive atmosphere) — *Standard specification for actuators*.
Gc: Enhanced Protection; suitable only for Zone 2 (Explosive atmosphere unlikely under normal operation).
3.3 Explosion-proof Type Selection Guide
3.3.1 Standard Type
Most Common Specification: Ex d IIB T4 Gb + IP65
Suitable for general industrial environments.
3.3.2 Outdoor Type (Weatherproof)
Waterproof, dustproof, and UV-resistant.
Suitable for open-air installation.
3.3.3 Underwater Type
For standard underwater applications, explosion protection is generally not a concern; selecting an IP68 rating is sufficient.
However, if the medium is explosive, or if the surrounding area is classified as an explosion-hazard zone, the appropriate explosion-proof rating must be selected based on actual site conditions.
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Installation Methods
Key Distinction: The control unit (containing electronic control components such as the controller, contactors, transformer, display screen, buttons, etc.) is integrated directly with the actuator body (motor + reduction mechanism + limit/torque switches).
4.1 Integrated Type
The motor and control unit are integrated into a single assembly, facilitating easy installation; the actuator mounts directly onto the valve (via a standard ISO 5211 interface), resulting in a compact structure.
4.1.1 Definition:
The motor, gearbox, and control unit (control box) are all encapsulated within a single compact housing, forming a “plug-and-play” integrated unit. No additional external control cabinet is required.
4.1.2 Installation Features:
The actuator mounts directly onto the butterfly valve via an ISO 5211 flange; on-site installation requires connecting only the main power supply and control signal cables.
– Convenient and Rapid Installation: Wiring is highly simplified, resulting in significant savings on cabling, control cabinets, and installation labor costs. Commissioning can be performed using local buttons, an LCD screen, or via Bluetooth/magnetic tools, eliminating the need to frequently open the housing cover.
– Compact Size, Minimal Footprint: Ideal for installation in pipe galleries or equipment rooms with limited space.
– Suitable for general industrial environments (e.g., water treatment, HVAC, wastewater treatment plants), space-constrained locations, and projects requiring rapid installation and intelligent monitoring capabilities.
4.2 Separate type
The Separate type (featuring a remotely installed control unit) is suitable for environments characterized by high temperatures, vibration, or explosion hazards.
4.2.1 Definition:
The actuator body (motor + mechanical components) is installed separately from the control unit. The control unit connects to the actuator body via a multi-core cable and can be installed at a distance of tens or even hundreds of meters away.
4.2.2 Installation Features:
The actuator body is mounted directly onto the valve, while the control unit can be installed in a control room, on an equipment platform, or at a location situated remotely from the valve. The control box can be installed remotely, making it particularly suitable for environments characterized by high temperatures, vibration, explosive hazards, severe corrosion, or high humidity.
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Classification by Functional Expansion Options
5.1. Equipped with a Manual Handwheel Mechanism
Enables manual operation in the event of a power failure.
5.2. Equipped with Position Feedback
Outputs a valve position signal (indicating the degree of opening/closure).
Used for integration into monitoring and control systems.
5.3. Equipped with Limit Switches and Torque Protection
Prevents damage caused by overload (this option may be omitted if the unit is equipped with a gearbox/reducer).
Enhances operational safety.
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Key Considerations for Engineering Selection
when selecting an electric actuator, focus primarily on these five key points:
Torque Matching (The Most Critical Factor)
Control Mode (On/Off Switching vs. Modulating/Regulating)
Mounting Configuration (Integrated vs. Remote/Split-type)
Environmental Requirements (e.g., Waterproofing and Explosion-proofing)