Control valve positioners are essential devices used to enhance the performance and accuracy of control valves by providing precise positioning of the valve plug or disc in response to control signals from the process controller or transmitter. There are several types of control valve positioners, each with specific features and functionalities. Here are some common types of control valve positioners:

1. Pneumatic Positioners:

   • Pneumatic positioners are widely used in industrial applications and operate based on the principle of using pneumatic pressure to position the valve actuator according to the control signal.
   • These positioners receive an input signal from the process controller or transmitter and adjust the air pressure to the actuator to position the valve plug or disc accurately.
   • Pneumatic positioners are suitable for use with pneumatic actuators and are often used in process control systems in industries such as chemical processing, oil and gas, power generation, and water treatment.

2. Electro-Pneumatic Positioners:

   • Electro-pneumatic positioners combine pneumatic and electronic components to provide precise control and positioning of control valves.
   • These positioners receive an electronic input signal from the process controller or transmitter and convert it into a pneumatic output signal to adjust the actuator position.
   • Electro-pneumatic positioners offer improved accuracy, responsiveness, and flexibility compared to pneumatic positioners and are suitable for applications requiring precise control of valve position.

3. Digital Positioners:

   • Digital positioners utilize digital technology and microprocessors to control and position control valves accurately.
   • These positioners receive digital input signals from the process controller or transmitter and use advanced algorithms and feedback mechanisms to adjust the valve position.
   • Digital positioners offer enhanced performance, diagnostics, and communication capabilities compared to pneumatic and electro-pneumatic positioners. They may also include features such as self-calibration, adaptive tuning, and predictive maintenance.

4. Smart Positioners:

   • Smart positioners are advanced digital positioners equipped with additional features such as diagnostics, communication protocols, and self-calibration capabilities.
   • These positioners can communicate with the control system using digital communication protocols such as HART (Highway Addressable Remote Transducer), Foundation Fieldbus, or Profibus.
   • Smart positioners provide real-time feedback on valve performance, health status, and diagnostic information, allowing for proactive maintenance and troubleshooting.

5. Pneumatic-Hydraulic Positioners:

   • Pneumatic-hydraulic positioners combine pneumatic and hydraulic components to control and position control valves in high-pressure or high-force applications.
   • These positioners use pneumatic pressure to control a hydraulic actuator, which in turn positions the control valve.
   • Pneumatic-hydraulic positioners are suitable for applications requiring high thrust or force, such as large-diameter valves or high-pressure steam systems.

These are some common types of control valve positioners used in industrial process control systems. The selection of a specific type of positioner depends on factors such as the type of valve, actuator, process requirements, and control system architecture.