What is a Butterfly Valve Actuator? 

An actuator automates the opening, closing, and throttling of a butterfly valve disc; the actuator is connected to the stem of the butterfly disc. When it receives a signal, it converts energy from electricity, hydraulic fluid, or compressed air into motion that rotates the disc and controls the flow of fluid. 

Butterfly Valve Actuator Types 

Electric Butterfly Valve Actuators 

Electric actuators convert electrical energy from motors into mechanical motion. When the actuator receives a signal (AC/DC power, analog 4–20 mA, or digital control from a PLC or DCS system), its motor turns on. The rotational force is transferred through reduction gears to rotate the valve rod, which then rotates the disc from 0° to 90° to regulate flow.  

Pros: Precise positioning, remote control, and ease of integration with electrical control systems. 

Cons: Operates slower than other options. 

Pneumatic Butterfly Valve Actuators 

Pneumatic actuators convert the energy from compressed air to create mechanical motion. When compressed air is supplied to the pneumatic actuator, the air pressure is used to move a diaphragm, piston, or an axis rack to produce torque. The torque generated is transmitted by the shaft to rotate the disc. 

Pros: Fast response times and safe to use in explosive environments. 

Cons: Requires additional infrastructure for air supply. 

What Does SR and DA Mean? 

In pneumatic actuators, SR (Spring Return) and DA (Double Acting) refer to two actuator types. 

Spring Return Actuators 

A spring return actuator is a single-acting actuator with a spring return (SR) functionality and a single air chamber. The single-acting pneumatic actuator uses air to open the valve and a mechanical spring to close the valve in a normally closed configuration. It can also be configured the other way around in a normally open configuration. 

Spring return actuators are ideal for applications where safety is a top priority since these valves return to a predefined position when power and/or air pressure are lost. This makes them a reliable, fail-safe option. 

Double-Acting Actuators 

A double-acting (DA) actuator has one chamber but no internal spring; due to this, they require an external air supply. Compressed air enters either end of the chamber, causing the piston to move back and forth, opening and closing the valve.  

Double-acting actuators are ideal for high-force output and fast action. They are also known for their longevity since they require less maintenance compared to spring return actuators, due to the absence of the mechanical spring. However, they are not failsafe, if the air pressure fails, they stay in the current position and can’t be opened or closed until the air service is restored. 

Hydraulic Butterfly Valve Actuators 

Hydraulic actuators have a pressurized cylinder or fluid motor that converts energy from hydraulic pressure (typically oil) into mechanical motion. When hydraulic oil enters the actuator chamber, it moves a piston, which then rotates the valve rod and disc. When the hydraulic oil flows in reverse or is discharged, the disc rotates back. 

Pros: Ideal for high-pressure applications. 

Cons: Higher cost, takes longer to gain speed, and is more complex due to fluid management requirements. 

What Does a NO and NC Actuator Position Mean? 

Normally Open (NO) and Normally Closed (NC) positions in electric and pneumatic actuators determine the default state of the valve. In a Normally Open valve, the valve remains open until air or electricity is applied, and the piston will move and close the valve. In a Normally Closed valve, it’s the opposite. 

If power is lost, spring return pneumatic actuators automatically return to the selected position, either normally open (NO) or normally closed (NC), as will spring return electric actuators.  

Linear vs. Rotary Actuators 

Linear and rotary actuators determine the direction of motion. 

Linear Horizontal Actuators  

Linear actuators create motion in a straight line, either in an up-and-down motion or a back-and-forth motion. This motion is converted to rotary motion through rack and pinion gears. 

While expensive, these actuators are ideal for precise positioning, low power consumption, and easy control. 

Rotary Actuators 

Rotary actuators create circular motion, turning objects around a fixed point (axis). 

There are different types of rotary actuators available, determining the amount of rotation they can produce. Electric rotary actuators offer unlimited rotation, while pneumatic or hydraulic rotary actuators have limited rotation. 

This type of actuator is ideal for applications requiring high torque and smooth, continuous rotation. 

Conclusion 

A butterfly valve actuator automates the opening, closing, and throttling of a butterfly valve disc by converting energy from electricity, hydraulic fluid, or compressed air into motion. All three actuator types and subtypes have a unique set of advantages and challenges. Choosing the right actuation type and subtype, along with the correct valve default state, will ensure efficient and safe automated system operation.