Selecting the correct pneumatic actuator torque is one of the most important steps in valve automation.

An actuator that is too small may not generate enough torque to fully open or close the valve. An actuator that is unnecessarily large can increase equipment cost, compressed air consumption, and overall system size.

For industrial valve applications, the goal is not simply to choose the largest actuator.

The correct approach is to match the actuator's available output torque with the valve's actual operating torque under the required working conditions.

A basic selection principle is:

Actuator Output Torque ≥ Valve Required Torque × Safety Factor

But how do you determine the required torque?

What factors affect valve torque?

And how do you select the correct pneumatic actuator size?

This guide explains the key factors engineers should consider when selecting a pneumatic actuator for ball valves, butterfly valves, and other quarter-turn valves.

1. What Is Pneumatic Actuator Torque?

Pneumatic actuator torque is the rotational force generated by an actuator.

It is normally expressed in:

• N·m
• Nm
• lb·in
• lb·ft

For quarter-turn valves such as ball valves and butterfly valves, the actuator converts the linear movement of the piston into rotational movement.

The actuator torque is transmitted through the drive shaft to rotate the valve.

In simple terms:

Compressed Air → Piston Force → Mechanical Transmission → Rotational Torque → Valve Movement

The actuator must generate sufficient torque throughout the entire valve operating cycle.

2. Why Is Correct Torque Selection Important?

Correct torque selection directly affects valve reliability.

If the actuator torque is too low, several problems may occur:

• Valve cannot fully open
• Valve cannot fully close
• Valve may stop during operation
• Incomplete sealing may occur
• Actuator may operate under excessive load
• Valve automation may become unreliable

On the other hand, selecting an actuator with excessive torque may also be undesirable.

An oversized actuator can result in:

• Higher equipment cost
• Larger installation space
• Higher air consumption
• Greater mechanical loading
• Potential damage to the valve stem or internal components if improperly configured

Therefore:

Too Little Torque → Insufficient Valve Operation

Too Much Torque → Unnecessary Oversizing

The objective is to find the appropriate actuator size with a suitable operating margin.

3. Step 1: Determine the Valve Type

The first step is identifying the valve that the actuator will operate.

Common quarter-turn valves include:

Ball Valve

Ball valves generally require torque to overcome:

• Seat friction
• Packing friction
• Differential pressure
• Medium-related forces

Ball valve torque can vary significantly depending on the seat material, pressure, temperature, and valve construction.

Butterfly Valve

Butterfly valve torque can be influenced by:

• Disc size
• Seat material
• Differential pressure
• Disc position
• Medium
• Shaft and bearing friction

The torque may not remain constant throughout the entire opening and closing cycle.

Plug Valve

Plug valves can require relatively high torque because of friction between the plug and sealing surfaces.

Therefore, actuator selection should always start with the actual valve type and manufacturer's torque data.

4. Step 2: Find the Valve Operating Torque

The most important number in actuator sizing is the valve operating torque.

Valve manufacturers may provide torque values at different conditions, such as:

• Breakaway Torque
• Running Torque
• Seating Torque
• Unseating Torque
• Maximum Torque

For some valves, the torque required to start opening is different from the torque required during continuous movement.

For example:

Breakaway Torque

The torque required to initially move the valve from the closed position.

Running Torque

The torque required while the valve is moving.

Seating Torque

The torque required to move the valve into its final closed position.

Unseating Torque

The torque required to move the valve away from the closed position.

When selecting an actuator, engineers should identify the highest relevant valve torque rather than selecting the actuator based only on running torque.

5. Step 3: Consider Differential Pressure

Differential pressure can significantly affect valve operating torque.

For example, a ball valve operating at a high pressure differential may require more torque to move the ball against the pressure and sealing forces.

For butterfly valves, differential pressure can also influence disc torque.

Therefore, valve torque should be evaluated under the actual operating conditions.

Consider:

• Maximum working pressure
• Differential pressure
• Minimum and maximum pressure
• Valve position
• Medium characteristics

A torque value measured under low-pressure conditions should not automatically be used for a high-pressure application.

6. Step 4: Consider the Valve Seat and Sealing Material

The valve seat has a direct influence on operating torque.

Common ball valve seat materials include:

• PTFE
• RPTFE
• PPL
• Metal Seat

Different materials have different friction characteristics and temperature capabilities.

For example, a metal-seat valve operating at high temperature may have different torque requirements from a soft-seat PTFE valve.

Similarly, butterfly valve seat materials can influence friction between the disc and seat.

Therefore:

Valve Size Alone Does Not Determine Actuator Torque.

Two valves with the same DN size can require different actuator torque.

7. Step 5: Consider Operating Temperature

Temperature can affect valve torque and sealing performance.

High-temperature applications may cause:

• Changes in seal friction
• Thermal expansion
• Changes in material properties
• Increased operating resistance

Low-temperature applications can also affect sealing materials and friction.

Therefore, actuator selection should be based on the valve torque under the actual temperature range.

For applications involving:

• Steam
• Hot water
• Thermal oil
• High-temperature gas
• Cryogenic media

the valve manufacturer's torque data should be carefully reviewed.

8. Step 6: Check the Available Air Pressure

Pneumatic actuator output torque depends strongly on the available air pressure.

In general:

Higher Air Pressure → Higher Available Actuator Force/Torque

Lower Air Pressure → Lower Available Actuator Force/Torque

However, the actual relationship depends on actuator design, piston area, mechanism, and position.

For example, an actuator rated at a certain torque at 6 bar should not automatically be expected to provide the same torque when the actual site pressure is significantly lower.

When selecting an actuator, confirm:

• Minimum air pressure
• Normal operating pressure
• Maximum air pressure
• Air pressure fluctuations

The actuator torque should be sufficient even under the lowest expected operating pressure.

9. Step 7: Choose the Safety Factor

A safety margin is normally included between the valve's required torque and the actuator's available torque.

A simplified selection method is:

Required Actuator Torque = Valve Torque × Safety Factor

For example:

If a valve requires:

100 N·m

and the selected safety factor is:

1.25

then:

100 × 1.25 = 125 N·m

The actuator should therefore provide at least approximately 125 N·m under the relevant operating condition.

However, the appropriate safety factor is not universal.

It depends on:

• Valve type
• Manufacturer recommendations
• Process conditions
• Torque uncertainty
• Operating frequency
• Temperature
• Medium
• Safety requirements

For critical applications, engineers should follow the valve and actuator manufacturer's sizing recommendations rather than applying an arbitrary safety factor.

10. Step 8: Check the Actuator Torque at Every Position

One common mistake is checking only the maximum actuator torque.

For rotary actuators, output torque can vary depending on the piston position.

This is particularly important for rack-and-pinion actuators.

The actuator should provide sufficient torque throughout the required valve stroke.

For example:

Valve Breakaway Torque

↓

Valve Running Torque

↓

Valve Seating Torque

The actuator output should satisfy the highest relevant torque requirement throughout the operating cycle.

11. Single Acting vs Double Acting Torque Selection

Actuator configuration also affects torque selection.

Single Acting Actuator

A single acting actuator uses compressed air in one direction and springs in the opposite direction.

The available torque changes as the spring is compressed or released.

Therefore, engineers should check the actuator's torque table for:

• Air torque
• Spring torque
• Minimum spring torque
• Maximum spring torque
• Opening direction
• Closing direction

Double Acting Actuator

A double acting actuator uses compressed air for both directions.

The available torque is primarily determined by:

• Air pressure
• Actuator size
• Piston area
• Mechanical design
• Piston position

Therefore, the torque table for a double acting actuator should be checked at the actual operating pressure.

12. Pneumatic Actuator Torque Example

Suppose a butterfly valve manufacturer specifies:

Required valve torque = 180 N·m

The application requires a safety factor of:

1.25

Then:

180 × 1.25 = 225 N·m

The selected actuator should therefore provide at least 225 N·m at the relevant operating condition.

But there is another important question:

Can the actuator provide 225 N·m at the minimum available air pressure?

If the site normally operates at 6 bar but may drop to 5 bar, the actuator should be checked at the lower pressure.

This is why actuator selection should be based on the complete operating condition rather than a nominal pressure value.

13. Common Mistakes When Selecting Actuator Torque

Mistake 1: Selecting by Valve DN Only

A DN100 valve does not automatically require one specific actuator size.

Torque depends on the valve design and operating conditions.

Mistake 2: Ignoring Differential Pressure

The same valve may require different torque at different pressure differentials.

Mistake 3: Using Maximum Air Pressure Instead of Minimum Air Pressure

An actuator may generate sufficient torque at 7 bar but fail to meet the requirement at 5 bar.

Always consider the minimum expected air pressure.

Mistake 4: Ignoring Seat Material

Different seat materials can produce different friction and operating torque.

Mistake 5: Checking Only Running Torque

Breakaway and seating torque may be higher than running torque.

Mistake 6: Oversizing the Actuator

A larger actuator is not automatically a better choice.

The actuator and valve should be properly matched.

14. Pneumatic Actuator Torque Selection Checklist

Before selecting the actuator, collect these parameters:

Once these parameters are available, actuator selection becomes much more straightforward.

15. How to Select a Pneumatic Actuator for a Ball Valve

For a pneumatic ball valve, the basic selection process is:

Step 1

Determine the ball valve size and pressure rating.

Step 2

Obtain the valve manufacturer's operating torque.

Step 3

Identify the highest relevant torque:

Breakaway / Running / Seating / Unseating

Step 4

Apply the appropriate safety margin.

Step 5

Check the actuator torque at the actual minimum air pressure.

Step 6

Select single acting or double acting according to the fail-safe requirement.

Step 7

Confirm the actuator mounting interface and valve stem dimensions.

This process helps prevent both undersizing and unnecessary oversizing.

16. How to Select a Pneumatic Actuator for a Butterfly Valve

For butterfly valves, actuator selection should consider the torque curve throughout the valve's movement.

Important factors include:

• Valve DN
• Differential pressure
• Seat material
• Disc design
• Operating temperature
• Required cycle frequency
• Valve torque curve

The actuator must provide sufficient torque to:

Break Away → Move → Seat

A torque table from the butterfly valve manufacturer is therefore extremely useful for actuator sizing.

17. Why Actuator Construction Matters

Torque capacity is not determined by piston size alone.

The mechanical construction of the actuator also affects:

• Torque transmission
• Efficiency
• Durability
• Stability
• Service life

Important components include:

• Piston
• Rack
• Pinion
• Cylinder
• End cap
• Spring
• Bearings
• Seals
• Drive shaft

For industrial applications, corrosion resistance and mechanical durability are also important.

KINKO pneumatic actuators use aluminum alloy construction and hard anodizing treatment.

The actuator piston uses 65# steel with surface treatment designed to improve durability and corrosion resistance.

The deep piston structure provides sufficient space for spring installation in spring-return configurations.

18. KINKO Pneumatic Actuator Torque Solutions

KINKO provides pneumatic actuators for automated industrial valves, including:

• Double Acting Pneumatic Actuators
• Single Acting Pneumatic Actuators
• Rack and Pinion Actuators
• Heavy-Duty Actuators
• Scotch Yoke Actuators
• Explosion-Proof Configurations

KINKO actuators are designed for applications requiring reliable pneumatic valve automation.

Key features include:

Aluminum Alloy Body

Hard Anodized Surface Treatment

65# Steel Piston

IP68 Protection

Long Cycle Life

For suitable configurations and operating conditions, selected KINKO actuator designs can support up to 1 million cycles.

Actual actuator life depends on operating pressure, air quality, lubrication, valve load, cycle frequency, temperature, and installation conditions.

19. Frequently Asked Questions

How do I calculate the required pneumatic actuator torque?

A basic method is:

Required Actuator Torque = Valve Operating Torque × Safety Factor

The valve torque should be based on the actual operating condition and the highest relevant torque requirement.

How much safety factor should I use?

There is no single safety factor suitable for every application.

The appropriate margin depends on the valve type, manufacturer recommendations, operating conditions, temperature, pressure, and application requirements.

Does valve DN determine actuator size?

No.

DN is useful for identifying the valve size, but actuator sizing should primarily be based on the valve's required operating torque and the actuator's available torque at the actual air pressure.

Does higher air pressure produce more actuator torque?

Generally, increasing pneumatic pressure increases the force generated by the actuator.

However, the actual output torque depends on actuator design and piston position.

Can I use the same actuator for different valve types?

Not necessarily.

Even valves with the same DN may have significantly different operating torque.

The actuator should be selected according to the specific valve torque requirements.

How do I select a single acting actuator?

Determine:

1. Valve operating torque
2. Required fail position
3. Minimum air pressure
4. Spring torque
5. Operating frequency

Then compare these requirements with the actuator's spring and air torque data.

How do I select a double acting actuator?

Determine the valve operating torque and minimum available air pressure.

Then select an actuator whose output torque exceeds the required valve torque with the appropriate safety margin.

Conclusion

Choosing the right pneumatic actuator torque is not simply a matter of matching the actuator to the valve DN size.

A reliable selection should consider:

Valve Torque + Air Pressure + Differential Pressure + Temperature + Seat Material + Safety Factor + Actuator Type

The basic principle is:

Actuator Output Torque ≥ Required Valve Torque × Appropriate Safety Margin

For ball valves and butterfly valves, engineers should pay particular attention to breakaway torque, running torque, seating torque, and the actuator's torque output at the minimum operating air pressure.

A correctly sized actuator can help improve valve automation reliability, reduce unnecessary equipment costs, and avoid problems caused by insufficient or excessive torque.

KINKO provides single acting and double acting pneumatic actuators for ball valves, butterfly valves, angle seat valves, and other industrial valve automation applications.

When selecting an actuator, provide:

Valve Type + DN Size + Valve Torque + Pressure + Temperature + Air Supply + Fail Position + Cycle Frequency

These parameters allow the actuator configuration and torque requirements to be evaluated more accurately.

KINKO — Reliable Valve Automation Solutions