What is the function of a positioner in an air operated valve actuator?

In the realm of industrial automation and fluid control systems, air operated valve actuators play a pivotal role. These actuators are responsible for opening and closing valves, regulating the flow of various substances such as liquids, gases, and steam. Among the essential components that enhance the performance of air operated valve actuators is the positioner. In this blog post, as a supplier of air operated valve actuators, I will delve into the functions of a positioner in an air operated valve actuator and why it is crucial for efficient and precise valve control.

Understanding Air Operated Valve Actuators

Before we explore the role of a positioner, let's briefly understand air operated valve actuators. These actuators use compressed air as a power source to generate the force required to operate valves. They are widely used in industries such as oil and gas, chemical processing, power generation, and water treatment due to their reliability, fast response, and ability to handle high pressures.

There are different types of air operated valve actuators, including piston actuators, diaphragm actuators, and External Tie-rod Scotch Yoke Air Cylinder. Each type has its unique design and operating principle, but they all share the common goal of converting the energy from compressed air into mechanical motion to open or close a valve.

The Role of a Positioner

A positioner is a device that is used in conjunction with an air operated valve actuator to precisely control the position of the valve. It receives a control signal from a process controller or a control system and adjusts the air pressure supplied to the actuator to move the valve to the desired position. Here are the key functions of a positioner in an air operated valve actuator:

1. Precise Positioning

One of the primary functions of a positioner is to ensure precise positioning of the valve. In many industrial processes, accurate control of the valve position is critical for maintaining the desired flow rate, pressure, or level of a substance. For example, in a chemical reactor, a small deviation in the valve position can lead to significant changes in the reaction conditions, potentially affecting the quality of the final product.

A positioner continuously compares the actual position of the valve with the desired position indicated by the control signal. If there is a difference between the two, the positioner adjusts the air pressure to the actuator to move the valve towards the desired position. This feedback control mechanism allows for very precise positioning, often with an accuracy of ±0.5% or better.

2. Compensation for Friction and Load Variations

Valves are subject to various forces and loads during operation, such as friction in the valve stem, pressure differentials across the valve, and changes in the process fluid properties. These factors can cause the valve to deviate from its desired position, leading to inaccurate control.

A positioner can compensate for these variations by adjusting the air pressure to the actuator. For instance, if the friction in the valve stem increases, the positioner will increase the air pressure to the actuator to overcome the additional resistance and maintain the valve in the desired position. This ensures that the valve operates consistently, regardless of the external factors that may affect its performance.

3. Fast Response

In some industrial processes, rapid changes in the valve position are required to respond to sudden changes in the process conditions. For example, in a safety shutdown system, the valve needs to close quickly to prevent a hazardous situation.

A positioner can provide a fast response by quickly adjusting the air pressure to the actuator. It can convert the control signal into an appropriate air pressure within a short time, allowing the valve to move rapidly to the desired position. This fast response capability is essential for maintaining the safety and efficiency of the industrial process.

4. Signal Conversion and Amplification

In many cases, the control signal from the process controller may not be suitable for directly operating the valve actuator. For example, the control signal may be an electrical signal (such as a 4 - 20 mA signal), while the actuator requires an air pressure signal.

A positioner can convert the electrical control signal into an air pressure signal and amplify it to a level that is sufficient to operate the actuator. This signal conversion and amplification function make it possible to interface the valve actuator with a wide range of control systems.

Types of Positioners

There are several types of positioners available, each with its own advantages and applications. The most common types include:

Pneumatic Positioners

Pneumatic positioners use compressed air as the power source for both the control and the operation of the actuator. They are simple, reliable, and suitable for applications where electrical power is not available or where there are strict explosion - proof requirements.

Electro - Pneumatic Positioners

Electro - pneumatic positioners convert an electrical control signal into a pneumatic signal. They offer the advantage of being able to interface with modern electronic control systems, providing more precise control and additional features such as digital communication.

Smart Positioners

Smart positioners are advanced electro - pneumatic positioners that incorporate microprocessor technology. They offer enhanced functionality, such as self - calibration, diagnostic capabilities, and the ability to communicate with a control system using digital protocols. Smart positioners can provide valuable information about the valve and actuator performance, allowing for proactive maintenance and troubleshooting.

Applications of Positioners in Different Industries

Positioners are widely used in various industries to improve the performance of air operated valve actuators. Here are some examples:

Oil and Gas Industry

In the oil and gas industry, positioners are used in valves for wellhead control, pipeline regulation, and refining processes. Precise control of the valve position is crucial for maintaining the safety and efficiency of the operations. For example, in a pipeline, a positioner can ensure that the valve opens and closes at the right time to control the flow of oil or gas, preventing over - pressurization and leaks.

Chemical Industry

In the chemical industry, positioners are used in valves for chemical reactors, distillation columns, and storage tanks. Accurate control of the valve position is necessary for maintaining the correct reaction conditions, preventing unwanted reactions, and ensuring the quality of the chemical products. Fail Close Scotch Yoke Pneumatic Actuator with positioners are often used in safety - critical applications to ensure that the valve closes automatically in case of a power failure or other emergencies.

Power Generation Industry

In the power generation industry, positioners are used in valves for boiler control, turbine control, and cooling water systems. Precise control of the valve position is essential for maintaining the efficiency of the power generation process and preventing equipment damage. For example, in a steam turbine, a positioner can control the steam flow rate to the turbine, optimizing the power output and reducing energy consumption.

Why Choose Our Air Operated Valve Actuators with Positioners

As a supplier of air operated valve actuators, we offer a wide range of products that are equipped with high - quality positioners. Our actuators and positioners are designed and manufactured to meet the strictest industry standards, ensuring reliable and efficient operation.

We have a team of experienced engineers who can provide technical support and assistance in selecting the right actuator and positioner for your specific application. Whether you need a Scotch Yoke with Hydraulic Manual Handwheels for a critical process or a simple piston actuator for a general - purpose application, we can provide you with the best solution.

In addition, we offer competitive pricing, fast delivery times, and excellent after - sales service. We understand the importance of your industrial process and are committed to providing you with the products and support you need to keep your operations running smoothly.

Conclusion

In conclusion, a positioner plays a vital role in an air operated valve actuator by providing precise positioning, compensating for friction and load variations, offering a fast response, and performing signal conversion and amplification. It is an essential component for ensuring the accurate and efficient control of valves in various industrial processes.

If you are in need of air operated valve actuators with positioners for your industrial application, we invite you to contact us for more information. Our team of experts will be happy to discuss your requirements and provide you with the best solution for your needs. Let's work together to improve the performance and reliability of your industrial process.

References

• Perry, R. H., & Green, D. W. (Eds.). (1997). Perry's Chemical Engineers' Handbook. McGraw - Hill.
• Crane Co. (2009). Flow of Fluids Through Valves, Fittings, and Pipe. Technical Paper No. 410.
• Fisher Controls International LLC. (2010). Control Valve Handbook. Emerson Process Management.