自動バルブの基礎：種類、トリガー、フェイルセーフ

A valve sits quietly—until the moment it must act fast. In a water plant, it may stop a backflow event. In a chemical line, it may isolate a leak before it becomes an incident. That’s the promise of an automatic valve: it changes position (open/close/modulate) in response to a signal or condition, without an operator turning a handwheel.

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What Is an Automatic Valve (and What It Isn’t)

An automatic valve is a valve plus an “automatic brain and muscle” (actuation + control). The valve body does the flow job (ball, butterfly, globe, gate), while the actuator and controls decide when and how far to move. In practice, “automatic valve” often refers to an actuated valve (electric or pneumatic) or a self-acting valve (like a float valve or pressure regulator).

You’ll also hear related terms:

• Automated valve: usually implies an actuator driven by power (electric/air/hydraulic) and controlled by signals.
• Automatic control valve: often a modulating control valve in a loop (PID), not just open/close.
• Shutoff / ESD valve: emphasizes safety function and quick isolation.

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The Core Building Blocks of an Automatic Valve

Most industrial automatic valves break into four layers. When I’m troubleshooting a “valve won’t move” call, I check them in this order because it isolates faults quickly.

1. Valve body & trim: defines flow capacity (Cv), leakage class, pressure rating, materials, and sealing.
2. Actuator: provides torque/thrust—electric motor geartrain or pneumatic piston/spring-return.
3. Control & signals: PLC/DCS commands (on/off, 4–20 mA, fieldbus), local control station, interlocks.
4. Feedback & protection: limit switches, position transmitter, torque switches, overload protection, alarms.

For actuator fundamentals, AOXIANG has a clear overview in electric valve actuator control basics.

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Types of Automatic Valves (By Function and Motion)

Choosing the right automatic valve starts with defining the job: isolate, regulate, protect, or maintain a level/pressure. Then match the valve motion and actuator style.

1) On/Off (Isolation) Automatic Valves

These valves move fully open or fully closed. Typical pairings:

• Ball valve + quarter-turn actuator (common for tight shutoff)
• Butterfly valve + quarter-turn actuator (large diameter, lower cost)
• Gate valve + multi-turn actuator (high pressure/line isolation)

If you’re deciding between simple on/off vs regulation, the distinctions in control valve modulation onoff help prevent the classic mis-spec of “trying to modulate an on/off package.”

2) Modulating (Control) Automatic Valves

These adjust position continuously to hold a setpoint (flow, pressure, temperature, level). Common options:

• Globe control valve + pneumatic actuator + positioner (traditional high accuracy)
• Ball/butterfly with modulating electric actuator (popular where air isn’t available)

Modulating service depends on stable feedback, good tuning, and a valve sized to avoid hunting or poor rangeability.

3) Self-Acting Automatic Valves (No External Power)

These use the process itself or a mechanical float/spring:

• Float valves for tank level
• Pressure reducing/regulating valves
• Thermostatic mixing valves

They’re simple and robust, but they’re less flexible than instrumented actuation and usually provide limited diagnostics.

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Common Triggers: What Makes an Automatic Valve Move?

A valve doesn’t “think”—it responds to triggers. In industrial automation, these triggers come from instrumentation, logic, or safety systems.

Typical trigger sources include:

• Process instruments: pressure transmitters, flow meters, level sensors, temperature probes
• Control system outputs: PLC/DCS digital outputs (open/close) or analog (4–20 mA)
• Safety systems: ESD/SIS trip signals, fire & gas, high-high pressure/level
• Local events: manual pushbuttons, selector switches, local interlocks
• Mechanical conditions: float rise/fall, spring force, differential pressure

Mechanical Spring-Return Fail-Safe Electric Actuator

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Fail-Safes: How Automatic Valves Behave When Things Go Wrong

The most important question is not “How does it open?” but “What happens on loss of power/air/signal?” A good automatic valve design makes the safe state predictable and testable.

The Three Most Common Fail Actions

• Fail-Closed (FC): isolates the line on failure (common for hazardous fluids).
• Fail-Open (FO): maintains flow on failure (common for cooling water to prevent overheating).
• Fail-In-Place (FIP): holds last position (often with electric actuators unless a stored-energy system is added).

In my field experience commissioning valve packages, most unexpected shutdowns come from a fail action that was assumed—but never written into the cause & effect matrix.

How Fail-Safe Is Achieved (Typical Methods)

• Spring-return pneumatic actuator: spring drives to FC or FO when air is lost.
• Double-acting pneumatic + accumulator: stored air provides one last stroke.
• Electric actuator + battery/supercap: performs a power-loss stroke (application dependent).
• Mechanical latching / brake: prevents drift but doesn’t “move to safe” by itself.

For broad actuator selection considerations (torque, duty cycle, environment), see select valve actuator electric motor.

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Sizing and Selection: The Practical Checklist Engineers Use

A reliable automatic valve is rarely about one component—it’s about the match between process conditions, valve body, actuator output, and control philosophy. Here’s the short checklist I use to avoid undersized actuators and unstable control.

Process & Mechanical

• Line size, pressure class, temperature range
• Media properties (corrosive, viscous, solids, flashing/cavitation risk)
• Required shutoff tightness / leakage class
• Required flow (Cv) and allowable pressure drop
• Valve type suitability (ball vs butterfly vs globe)

Actuator & Control

• Required torque/thrust with safety factor (include breakaway, seating/unseating)
• Duty cycle and operating speed (strokes per hour, modulating duty)
• Power availability: electric supply vs instrument air quality
• Control interface: on/off, 4–20 mA, fieldbus; local/remote requirements
• Feedback: limit switches vs continuous position transmitter

Environment & Compliance

• Area classification (hazardous area requirements such as ATEX/IECEx where applicable)
• Ingress protection (IP rating), ambient temperature, corrosion category
• Functional safety needs (SIL-rated components when required)

For third-party background on functional safety concepts, reference the IEC 61511 overview and practical process safety guidance from CCPS (AIChE). For hazardous-area fundamentals, the EU ATEX guidance is a helpful starting point.

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Typical Problems (and How to Fix Them Fast)

Automatic valves often “fail” for predictable reasons. A structured approach reduces downtime and prevents repeated trips.

Common failure modes and remedies:

• Valve doesn’t move, actuator hums/tries
  • Check torque limit settings, mechanical binding, and valve stem/seat contamination.
• Pneumatic actuator slow or inconsistent
  • Verify air pressure/flow, filter-regulator condition, solenoid valve health, and tubing leaks.
• Position feedback wrong (shows open when closed)
  • Recalibrate limit switches/position transmitter; confirm cam orientation and wiring.
• Control loop hunts (modulating valve oscillates)
  • Recheck sizing (Cv too large), tune PID, add positioner/characterization if needed.
• Unexpected trip during power event
  • Confirm fail-safe design (FC/FO/FIP), add UPS or stored-energy stroke if required.

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Where AOXIANG Fits: Cost-Effective Automation Without Losing Reliability

In many plants, the goal is straightforward: automate more valves without multiplying maintenance headaches or budget. AOXIANG focuses on industrial-grade electric and pneumatic actuator solutions designed for high speed, low maintenance, and protective features like overload protection and remote monitoring—capabilities that matter in water treatment, chemicals, petroleum, new energy, and offshore environments.

From what I’ve seen in real installations, the biggest operational win comes when actuator selection, fail-safe definition, and feedback signals are standardized across the site. That standardization reduces spares, speeds commissioning, and makes operator training easier—often delivering more value than any single feature.

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Conclusion: Making the Automatic Valve “Boring” Is the Goal

A good automatic valve is almost invisible day-to-day—because it moves when it should, reports what it did, and fails safely when it must. If you define the trigger logic, choose the right valve/actuator pairing, and specify fail action up front, you’ll prevent most of the costly surprises that show up during startups and power/air disturbances.

If you’re planning an automation upgrade, share your valve type, media, pressure/temperature, and desired fail position in the comments—those four details usually narrow the best options quickly.

📌 aox q non invasive integrated electric valve actuator

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FAQ: Automatic Valve Questions People Search

1) What is an automatic valve used for?

An automatic valve is used to open, close, or regulate flow automatically based on a signal (PLC/DCS) or a condition (pressure/level/temperature), reducing manual operation and improving safety and consistency.

2) What’s the difference between an automatic valve and a solenoid valve?

A solenoid valve is usually a small, direct-acting or pilot valve controlled electrically. An automatic (actuated) valve often refers to larger process valves (ball/butterfly/globe) moved by an electric or pneumatic actuator, sometimes using a solenoid only as a pilot.

3) Does an automatic valve need electricity?

Not always. Many automatic valves are pneumatic (need air) or self-acting (float/pressure regulator). Electric-actuated valves, however, do need electrical power and control signals.

4) What does “fail-closed” mean on an automatic valve?

Fail-closed means the valve will move to the closed position when it loses power, air supply, or control signal—depending on the design—so the line is isolated in an upset.

5) Can a ball valve be used as a modulating automatic valve?

Sometimes, yes—but it depends on seat design, control requirements, and sizing. Many ball valves are best for on/off; for stable control, globe valves or characterized control valves are often better.

6) How do I choose between electric and pneumatic automatic valves?

Choose based on available utilities (power vs air), required fail-safe action, speed, duty cycle, environmental classification, and maintenance strategy. Electric is common where instrument air isn’t available; pneumatic spring-return is common for fast, clear fail-safe action.

7) Why does my automatic valve chatter or oscillate?

Chatter is often caused by oversizing, poor PID tuning, insufficient signal filtering, sticky valve mechanics, or unstable air supply/positioner behavior in pneumatic systems. Adjust sizing and tuning first, then check friction and feedback calibration.