Choosing Electric or Pneumatic Valve Actuators - SNBV FLOW

Introduction

Valve actuators can be categorized into manual and automatic types. Manual operation can use handwheels, handles, or gear drives, while automatic operation includes pneumatic valves, electric valves, hydraulic, and their combinations. With the development of industrial production and increased automation, valves requiring centralized control, remote control, and program control, those in hazardous areas inaccessible to humans, those needing rapid action, and those needing synchronized operation with other devices all necessitate electric, hydraulic, or pneumatic actuators. Statistics show that a refinery processing 5 million tons annually uses up to electric actuators.

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Classification of Valve Actuators

1. By Power Source Type:
   • Manual: Operated by human force.
   • Pneumatic: Uses compressed air, including pneumatic ball valves, pneumatic gate valves, pneumatic globe valves, and pneumatic butterfly valves.
   • Hydraulic: Driven by oil or water pressure.
   • Electric: Powered by electromagnets or motors, including electric ball valves, electric gate valves, electric globe valves, and electric butterfly valves.
   • Recent advancements include gas-liquid linkage, electro-hydraulic linkage, and self-actuating emergency shutoff devices.
2. By Stem Movement Form:
   • Multi-turn Actuators: The output shaft rotates more than one full turn, suitable for gate, globe, throttle, and diaphragm valves.
   • Part-turn Actuators: The output shaft rotates less than one full turn, used for ball, butterfly, and plug valves.
   • The primary connection standards are ISO and ISO , suitable for multi-turn and part-turn valve actuator attachments, respectively.
   
   Note:
   1. ISO standard
   2. ISO standard

Comparison of Valve Actuator Features

1. Manual Actuators:
   • Basic and limited by human strength.
   • Small valves can be operated directly; larger valves may require a gearbox for easier operation.
   • Handwheels are typically installed on globe and gate valves, while handles are used for butterfly valve ball valves, and plug valves.

2. Electric Actuators:
   • Advantages: High stability, constant thrust, and high control precision. The largest actuators can generate up to 225,000 kgf of thrust.
   • Can switch between direct and reverse action easily with a servo amplifier, and maintain position in case of a fault.
   • Types include part-turn and multi-turn electric actuators, used for valves like electric ball valves, electric butterfly valves, and electric gate valves.

3. Pneumatic Actuators:
   • Advantages: Fast action, reliable, and easy control. Typically operate with a 0.4-0.7 MPa air source, with special units up to 5-10 MPa.
   • Operate in temperatures from -15 to 80°C, some up to -60 to 120°C. Use compressed air or nitrogen as the power source.
   • Common in remote and automated valve controls.

4. Hydraulic Actuators:
   • Components: Power source, control section, and actuator.
   • Advantages: Simple, compact, large output force, stable, and reliable. Allows for easy speed adjustment and remote control.
   • Disadvantages: Viscosity changes with temperature, potential for leaks, complex piping, and maintenance. Not suitable for signal processing, and not recommended for flammable or explosive environments.
5. Gas-Liquid Linkage Actuators:
   • Often used in gas pipelines and areas without power sources, utilizing the gas in the pipeline as the power source.
   • Advantages: Compact, stable transmission, large output torque, adjustable torque, and suitable for various automatic control methods.
   • Disadvantages: Expensive and complex structure.

Conclusion

Valve actuators play a critical role in modern industrial operations, providing necessary control and automation. They are classified by power source and stem movement, each with unique advantages and drawbacks. Understanding these distinctions is vital for selecting the right actuator for specific industrial applications.

FAQs

1. What is the main advantage of electric actuators over pneumatic ones?
   • Electric actuators offer higher control precision and maintain their position in case of a fault, unlike pneumatic actuators that require a backup system.
2. Why are hydraulic actuators not recommended for flammable environments?
   • Hydraulic actuators use oil, which can pose a risk in flammable environments due to potential leaks and oil's flammable nature.
3. How does a gas-liquid linkage actuator work without an external power source?
   • It uses the gas present in the pipeline as its power source, making it ideal for remote locations without an external power supply.
4. What is the typical operating pressure range for pneumatic actuators?
   • Pneumatic actuators usually operate within 0.4-0.7 MPa, with special versions handling pressures up to 5-10 MPa.
5. What standards are used for valve actuator connections?
   • The primary standards are ISO for multi-turn actuators and ISO for part-turn actuators, ensuring proper connection dimensions for different valve types.

Recommended actuator manufacturers

Type Manufacturer Place of origin Official website Electric Actuators ROTORK Britain www.rotork.com Electric Actuators Limitorque® United States www.flowserve.com Electric Actuators AUMA Germany www.auma.com Electric Actuators &
Pneumatic Actuators Biffi Italy biffi.it Pneumatic Actuators SMC Japan www.smcworld.com Pneumatic Actuators Festo Germany www.festo.com

This guide offers detailed insights into pneumatic actuators, exploring various types such as diaphragm, piston, and valve actuators. It provides a thorough analysis of their applications and benefits, including rapid response times and robust performance in challenging environments. The guide is designed to aid in selecting the optimal control valve actuator by addressing critical factors such as fluid type, pressure conditions, and actuator force requirements. By focusing on these essential considerations, it equips engineers and technicians with the knowledge needed to boost system efficiency and ensure seamless integration with existing control frameworks.

I. Introduction

When it comes to the selection of actuators for pneumatic actuator control valve, the choice is often complex and multifaceted. Among the range of options available, pneumatic actuators stand out due to their simplicity, reliability, and cost-effectiveness. Pneumatic actuators convert energy formed by vacuum or compressed air at high pressure into either linear or rotary motion. Their applications are far-reaching, encompassing sectors from manufacturing to energy production. In the following sections, we delve deeper into the considerations for selecting pneumatic actuators, the types available, and their individual advantages and drawbacks.

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II. Understanding Pneumatic Actuator Control Valve

A. Pneumatic Actuator Control Valve: Definition and Role

A pneumatic actuator control valve is a mechanical device that uses compressed air to control the motion of the control valve. It achieves this through the conversion of the energy from the compressed air into mechanical motion. This mechanical motion, either linear or rotary, is then used to control the position of the control valve stem, thereby regulating the flow of fluid through the valve. In essence, the pneumatic actuator acts as the intermediary between the control system and the physical valve, reaching a position that corresponds to the control signal. It plays a crucial role in ensuring precise control over valve operations, often finding applications in industries where maintaining specific flow rates, pressures, or temperatures are critical for effective functioning.

B. Energy Conversion in Pneumatic Actuator Control Valve

The conversion of energy into linear or rotary motion in a pneumatic actuator control valve is achieved via a simple yet highly effective mechanism. When compressed air enters the actuator, it creates a force which pushes against a piston or a diaphragm inside the actuator. This force moves the piston or diaphragm, which in turn is connected to the valve stem, causing it to move.

In the case of linear motion, the air pressure directly pushes the piston, causing it to move in a straight line. Since the piston is directly linked to the valve stem, this linear movement translates into the opening or closing of the valve, thereby controlling the fluid flow.

For rotary motion, a similar principle applies, but with an added component known as a rack-and-pinion. Here, the linear motion of the piston convert into rotary motion with the help of the rack-and-pinion mechanism. The piston is connected to a rack, a toothed bar, which moves as the piston moves. The rack&#;s teeth are meshed with a small gear (the pinion) that turns as the rack moves, thereby creating rotary motion. This rotation is passed onto the valve stem, which in turn moves the valve into open or closed positions.

In both cases, the control system can manipulate the compressed air&#;s pressure to precisely regulate the piston or diaphragm&#;s movements, thereby attaining the desired valve position.

C. Types of Pneumatic Actuator Control Valve

Pneumatic actuator control valves come in two primary types: spring return (also known as single acting) and double acting.

Spring Return Pneumatic Actuator

A spring return pneumatic actuator operates on a single supply of compressed air. The actuator holds a spring that compress when the air supply drives the piston or diaphragm to move the valve. When the air supply cut off, the energy stored in the compressed spring release, causing the piston or diaphragm to return to its original position and thus the valve to its default state. This design ensures that in the event of a failure in the air supply, the valve will return to a safe position (either fully opened or fully closed), making spring return actuators a popular choice for safety-critical applications.

Double Acting Pneumatic Actuator

Unlike its spring return counterpart, a double acting pneumatic actuator uses two supplies of compressed air. These air supplies are used alternately to move the piston or diaphragm in both directions, thereby opening and closing the valve. The advantage of a double acting actuator is that it offers more control over the valve&#;s operation and can hold it in any position, not just fully open or fully closed. However, in the event of an air supply failure, a double acting actuator will remain in its last position, which may not always be the safest option.

These two types of pneumatic actuators cater to different requirements and applications, and the choice between them depends on a variety of factors, including the nature of the process, the level of control required, and the safety considerations.

D. Certifications and Quality Control

When choosing a pneumatic actuator, it&#;s crucial to consider the quality and certifications of the manufacturer. Our company holds several industry-standard certifications, including ISO and CE, denoting our commitment to maintaining high-quality manufacturing processes and products. Additionally, each of our pneumatic actuators undergoes stringent quality control checks at each stage of production, ensuring their consistent performance and durability. Our in-house testing processes include rigorous checks for dimensional accuracy, operational efficiency, and durability under varying conditions. Furthermore, we dedicate to continual improvement, regularly reviewing and updating our quality control processes to ensure we remain at the forefront of technology and industry standards. By choosing our company, you are investing in reliable, high-quality pneumatic actuators that adhere to the most rigorous international safety and performance standards.

III. Factors to Consider when Selecting Pneumatic Actuator Control Valve

A. Application Requirements

The specific needs of your process or application are paramount in selecting a pneumatic actuator. Consider factors like the type of fluid being controlled, the required flow rate, and the operating pressure and temperature. These factors help determine the most suitable actuator type and specifications.

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B. Safety Requirements

The safety requirements of your operation play a critical role in your choice of actuator. For critical safety applications, a spring return actuator that defaults to a safe position in the event of air supply failure may be the best choice. In less critical scenarios where more control is desired, a double acting actuator could be more appropriate.

C. Availability of Compressed Air

The availability and pressure of the compressed air supply in your facility also affects your choice of actuator. Double acting actuators require two sources of air for operation, while spring return actuators can operate with a single air supply.

D. Quality and Certifications of the Manufacturer

The reliability and reputation of the manufacturer, as evidenced by their certifications and commitment to quality control, should also consider. This ensures that the actuator you choose is reliable, durable, and adheres to industry safety and performance standards.

IV. Best Practices for Selecting and Installing Pneumatic Actuator Control Valve

A. Understand Your Process Requirements

Before selecting a pneumatic actuator control valve, fully understand your process requirements. Identify the nature of the fluid, the required flow rate, and the operating pressure and temperature. This information is essential in choosing the right type of actuator and its specifications.

B. Evaluate Safety Needs

Assess the safety needs of your operation. If your operation must default to a safe position in case of air supply failure, consider a spring return actuator. If you need more control and can manage the risk of the actuator remaining in its last position during an air supply failure, a double acting actuator could be suitable.

C. Consider the Availability of Compressed Air

Check the availability and pressure of the compressed air supply in your facility. If you have two sources of air, a double acting actuator could be an option. If only a single air supply is available, a spring return actuator would be more suitable.

D. Consider the Manufacturer&#;s Reputation and Certifications

Investigate the manufacturer&#;s reputation, certifications, and commitment to quality control. These factors can provide reassurance that your selected actuator is reliable, durable, and meets industry safety and performance standards.

E. Proper Installation and Maintenance

Once you&#;ve selected the right pneumatic actuator, carefully follow the manufacturer&#;s instructions for installation to ensure optimal performance. Regular maintenance, as recommended by the manufacturer, is also crucial for the longevity of the actuator and overall efficiency of your operation.

FAQ

1. What is a pneumatic actuator control valve and how does it function?

A pneumatic actuator control valve is a device that uses compressed air to control the movement of a valve, adjusting the flow of fluids in a system. The pneumatic actuator converts the air pressure into mechanical motion, enabling precise regulation of flow rates by opening or closing the valve.

2. What are the different types of pneumatic actuator control valves?

There are several types, including diaphragm actuators, piston actuators, and vane actuators. Each type varies in design and application suitability, with diaphragm actuators being common for their simplicity and reliability, while piston actuators offer higher force capabilities.

3. What are the benefits of using pneumatic actuator control valves?

These valves offer several advantages, such as fast response times, high reliability in hazardous environments, and the ability to produce substantial force. Additionally, they are easy to maintain and can be integrated into automated control systems for efficient operation.

4. What are the typical applications of pneumatic actuator control valves?

Pneumatic actuator control valves are widely used in industries such as oil and gas, chemical processing, water and wastewater treatment, and food and beverage production. They are ideal for applications requiring robust and reliable flow control in dynamic conditions.

V. Conclusion

The selection of a suitable pneumatic actuator requires careful consideration of various factors. It begins with understanding the specific needs of your application, including the type of fluid, the required flow rate, and the operating pressure and temperature. Safety requirements are equally important, dictating whether a spring return or a double acting actuator is more suitable. The availability of the compressed air supply in your facility is another determinant, especially since double acting actuators require a double air supply. The manufacturer&#;s reputation, their certifications, and quality control commitment are also crucial to ensure the reliability and durability of the actuator. Lastly, proper installation and regular maintenance, according to the manufacturer&#;s instructions, are critical for optimal performance and longevity of the actuator.

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