Butterfly Valve Actuator Sizing: Torque & Selection Guide

Butterfly valve actuator sizing means selecting an actuator that can provide enough torque to operate the valve reliably while also meeting the required control functions under actual operating conditions.

In simple terms, actuator sizing mainly answers two questions:

• How much operating torque does the butterfly valve actually require?  
• Which actuator can provide sufficient torque under the actual working conditions?

Differential pressure, seat material, medium, temperature, and butterfly valve design can all affect the actual operating torque. 

Therefore, actuator selection should not be based on valve size alone. It should also consider the required valve torque, differential pressure, seat material, available air supply or power supply, and the required control method.

What Is Butterfly Valve Torque?

Butterfly valve torque is the rotational force required at the valve stem to open, close, or rotate the disc. It is usually expressed in N·m (Newton-meters).

If the actuator cannot provide enough torque for the actual valve requirement, the valve may not open or close properly, or it may fail to reach the fully sealed position.

The torque required by a butterfly valve is not the same throughout the entire opening and closing cycle. The main types of torque include:

• Breakaway Torque: The torque required to start opening the valve from the fully closed position.
• Running Torque: The torque required to rotate the disc during opening or closing.
• Seating Torque: The torque required as the valve approaches the fully closed position and the disc engages with the seat to achieve sealing.

For actuator sizing, it is usually not enough to consider only one of these torque values. The actuator should be selected based on the maximum operating torque that may occur under the actual working conditions.

In most cases, buyers do not need to calculate these torque values themselves. During actual actuator selection, the butterfly valve manufacturer usually provides torque data based on factors such as valve size, valve design, seat material, and differential pressure, and then selects a suitable actuator accordingly.

For a preliminary estimate, you can use our Butterfly Valve Torque Calculator to quickly obtain a reference torque based on valve size, differential pressure, and operating conditions.

The calculated result is intended for preliminary sizing only. The final actuator model should still be confirmed based on the actual valve torque data and the specific operating conditions.

How Is Actuator Torque Selected?

Once the required operating torque of the butterfly valve has been determined, the actuator is usually selected with an additional safety margin rather than being matched to the valve torque on a 1:1 basis.

This can be expressed with a simple formula:

Required Actuator Torque = Valve Torque × Safety Factor

For example, if the maximum operating torque required by the butterfly valve under actual working conditions is 200 N·m, and a safety factor of 1.25 is used:

200 × 1.25 = 250 N·m

This means the selected actuator should be able to provide at least 250 N·m of output torque under the actual operating conditions.

The safety factor provides additional margin for changes that may occur during operation, such as pressure fluctuations, changes in seat friction, or increased resistance after long-term use.

It is important to note that the safety factor is not a fixed value. It should be determined based on the valve design, medium, differential pressure, operating frequency, and the actuator manufacturer's sizing recommendations.

How to Select a Pneumatic Actuator

When selecting a pneumatic actuator, in addition to confirming the torque required by the butterfly valve, several key parameters should also be considered:

1. Air Supply Pressure

Air supply pressure directly affects the output torque that a pneumatic actuator can provide.

Common air supply pressures include:

• 4 bar
• 5 bar
• 6 bar

The same actuator model can provide different torque outputs at different air pressures. Therefore, actuator sizing should be based on the actual air pressure available at the installation site.

2. Double Acting or Spring Return

Pneumatic actuators are mainly available in two types:

• Double Acting: Compressed air is used to both open and close the valve.
• Spring Return: Compressed air drives the actuator in one direction, while a spring returns it to the preset position when the air supply is lost.

If the project requires the valve to automatically close or open in the event of air failure, the required fail position should be confirmed.

3. Control Type

If the butterfly valve only needs to fully open or fully close, a standard On-Off control setup can be used.

If the valve opening needs to be adjusted, a positioner is usually required.

4. Accessories

Depending on the project requirements, the actuator can also be equipped with accessories such as a limit switch box, solenoid valve, air filter regulator, or positioner.

• Limit Switch Butterfly Valve: Working Principle and Selection
• Pneumatic Butterfly Valve Basics: What It Is and How It Works
• A Complete Guide to Gear Operated Butterfly Valves
• Functions and Features of Different Butterfly Valve Actuators
• Find Your Match: Butterfly Valve Handle Types Explained

About the Author

Steven Jin

Sales Manager · Tianjin Union Valve Co., Ltd

More than 8 years of experience in the valve sales industry. Have extensive qualifications and experience.