Pneumatic Actuator Selection Guide: How to Choose the Right Size for Your Valve

Why Proper Pneumatic Actuator Sizing Matters

Correct actuator sizing ensures:

• Complete valve opening and closing

• Stable operation under varying pressure conditions

• Longer valve and actuator service life

• Reduced maintenance and energy consumption

Improper sizing can lead to valve stalling, air leakage, seal damage, or unsafe operation.

Step 1: Identify the Valve Type and Size

The first step in pneumatic actuator selection is determining the valve type and nominal size. Different valves require different operating torques or thrust forces.

Typical torque demand by valve type:

• Ball valve: High breakaway torque

• Butterfly valve: Torque varies with seat type and pressure

• Plug valve: Very high initial torque

• Globe valve: Linear thrust requirement

Larger valve sizes generally require higher actuator output.

Step 2: Determine Required Valve Torque or Thrust

Breakaway Torque vs. Running Torque

When selecting a pneumatic actuator, always consider:

• Breakaway (seating) torque – maximum torque required to open or close the valve

• Running torque – torque required during normal operation

The actuator must be sized based on the maximum required torque, not the average value.

Safety Factor

A safety factor is essential to compensate for wear, pressure fluctuations, and environmental conditions.

Recommended safety margins:

• On-off valves: 25–30%

• Control valves: 30–50%

• Severe service or high-cycle applications: 50% or more

Step 3: Check Available Air Supply Pressure

Pneumatic actuators rely on compressed air pressure to generate output force or torque. Common operating pressures include:

• 4 bar (58 psi)

• 5.5 bar (80 psi)

• 6 bar (87 psi)

• 8 bar (116 psi)

Lower air pressure requires a larger actuator to achieve the same output torque. Always size the actuator based on the minimum available air pressure, not the nominal value.

Step 4: Choose the Correct Actuator Type

Double-Acting Pneumatic Actuators

• Air pressure for both opening and closing

• Higher output torque

• Suitable for frequent operation

• No spring force limitation

Spring Return Pneumatic Actuators

• Air pressure for one direction, spring for the other

• Provides fail-safe function (fail-open or fail-close)

• Lower output torque compared to double-acting types

• Requires careful spring torque calculation

Spring return actuators must be sized based on the spring end torque, which is usually lower than air-driven torque.

Step 5: Match Actuator Torque Curve with Valve Torque Curve

Valve torque is not constant throughout the stroke. Similarly, actuator output torque varies depending on piston position.

Key consideration:

• Ensure actuator torque exceeds valve torque at every point of the stroke, especially at:

  • Valve breakaway position

  • Valve seating position

For high-performance butterfly valves or high-pressure ball valves, torque curve matching is especially important.

Step 6: Consider Environmental and Application Conditions

External factors can significantly affect actuator sizing:

• Ambient temperature (affects seals and lubrication)

• Corrosive or hazardous environments

• Outdoor installation

• High cycle frequency

• Emergency shut-down requirements

In harsh conditions, a larger actuator or higher safety factor is recommended.

Common Pneumatic Actuator Sizing Mistakes

Avoid these frequent errors:

• Ignoring breakaway torque

• Using nominal air pressure instead of minimum pressure

• Neglecting safety margins

• Oversizing without considering air consumption

• Not accounting for spring torque in fail-safe actuators

Pneumatic Actuator Selection Example

Final Checklist for Pneumatic Actuator Selection

Before finalizing your actuator size, confirm:

• Valve type, size, and torque data

• Breakaway and seating torque values

• Minimum air supply pressure

• Actuator type (double-acting or spring return)

• Required safety factor

• Environmental conditions

Conclusion

Choosing the right pneumatic actuator size for your valve is a critical step in ensuring safe, efficient, and reliable system operation. By understanding valve torque requirements, air pressure limitations, and actuator performance characteristics, you can confidently select an actuator that meets your application needs while optimizing cost and durability.