Doubleacting Actuators Boost Valve Automation Efficiency

Imagine a sprawling chemical plant with a labyrinth of pipes connecting reactors, storage tanks, and processing equipment. In this complex system, hundreds of valves silently regulate fluid flow. Without automation technology, each valve would require manual operation—an impractical and hazardous scenario. Workers in protective gear would need to navigate potentially dangerous environments, manually turning valve stems and handwheels to control media flow.

Valve actuators serve as the critical "automated brains" that replace manual operation, making valve control more efficient, safer, and more reliable.

Simply put, a valve actuator is a device that drives a valve's opening and closing movements. When paired with a valve, it forms a complete automated control unit. Without actuators, all valve operations would depend on manual labor—turning stems, rotating handwheels, or operating gearboxes.

The advent of actuators has significantly improved production efficiency, reduced labor costs, and enabled remote control in hazardous environments. They are indispensable components in modern industrial automation.

With diverse valve types—from ball valves to gate valves and butterfly valves—each requires specific actuators tailored to its application. Common actuator types include:

• Pneumatic actuators: Use compressed air as their power source
• Hydraulic actuators: Employ hydraulic fluid for greater force in high-pressure applications
• Electric actuators: Utilize electric motors with gear mechanisms

Pneumatic actuators, known for their reliability, simple maintenance, and cost-effectiveness, are widely used in industrial settings. This article focuses on an important pneumatic actuator type: the double-acting actuator.

Using compressed air as their energy source, pneumatic actuators offer a clean, safe, and readily available power solution. They come in two motion types:

• Linear pneumatic actuators: For valves requiring straight-line movement (e.g., globe valves)
• Rotary pneumatic actuators: For quarter-turn valves like ball and butterfly valves

Rotary pneumatic actuators typically use rack-and-pinion designs to convert linear air pressure into the 90-degree rotation needed for quarter-turn valves. Unlike single-piston linear actuators, rotary versions contain two pistons that move in opposite directions to rotate a central drive shaft.

These actuators feature two air ports controlling opposite piston movements:

• Air entering one port drives the valve open
• Air entering the opposite port drives it closed

This design enables precise valve control. In practice, solenoid valves typically manage air flow based on electrical signals from control systems, enabling remote automation.

Users can configure these actuators to fail-open or fail-closed based on safety requirements. This proves vital in hazardous material handling, where fail-closed configurations prevent leaks during air failures.

While lacking fail-safe capability, double-acting actuators offer distinct benefits:

• Compact size: No springs mean smaller, lighter designs—especially advantageous for large valves
• Lower cost: Simpler construction reduces manufacturing expenses
• Higher efficiency: Only overcoming valve torque (not spring resistance) improves performance

These make double-acting actuators ideal for non-critical applications prioritizing cost and space savings.

Choosing actuators requires evaluating multiple factors:

• Valve type and size
• Operating pressures and temperatures
• Media characteristics
• Safety requirements
• Budget constraints

• Prioritize single-acting actuators for fail-safe needs
• Choose double-acting for cost/space-sensitive, non-critical applications
• Consider hydraulic actuators for high-pressure/high-torque situations
• Opt for electric actuators when precision control is paramount

Valve actuators form the core of automation, replacing manual operation to enhance efficiency and safety. Both double-acting and single-acting pneumatic actuators serve distinct roles across industrial applications. Proper selection requires careful consideration of technical requirements and operational conditions.