Removes stiction | Removes effects | Positioner Control Valve Working Principle
A valve positioned is a device used to increase or decrease the air load pressure driving the actuator of a control valve until the valve’s stem reaches a position balanced to the output signal from the process variable instrument controller.
Positioner Control Valve Working Principle (2025 Updated Guide)
Positioner Control Valve is an invaluable part of up-to-date flow control systems. It ensures that the control valve opens to the required position as prompted by the control signal, thereby improving accuracy, stability, and system efficiency. A Positioner Control Valve is an integral one in the systems of modern flow control, which not only opens the valve to the correct position as indicated by the control signal, but also ensures that the process stabilizes and that the system functions at a level of greater efficiency and accuracy.
What Is a Positioner Control Valve?
The control valve positioner is an attachment to the actuator of the valve. It is designed to push or pull the valve spindle in the required direction by a controller signal (standardly 4-20 mA or pneumatic pressure). The positioner is the element that checks if the valve position meets the setpoint and also the part that, if needed, changes the pressure of the actuator to make the new position set.
Working Principle of Positioner Control Valve – Step-by-Step
1. Signal Reception:
The transmitter sends a signal to the positioner (DCS/PLC or control system).
Signal types are commonly: 4, 20 mA (electro-pneumatic), or 3, 15 psi (pneumatic).
2. Position Comparison:
- The positioner determines the exact position of the valve by the help of internal feedback like cams or sensors.
- It is this relative position that the positioner double-checks with the signal’s set point.Continuous Feedback Loop: The positioner is continuously monitoring and rectifying the valve position in real time; the positioner is thus the feedback loop.
Not a single moment does the positioner not monitor and change the valve position in real time.
The feedback loop is because the positioner is constantly monitoring and correcting the valve position.
3. Airflow Adjustment:
- In this case, the positioner will change the pneumatic actuator’s pressure with the help of the air supply to move the valve back to the starting or ending position if the given signal is between 3mA and 3.99mA or 16mA and 20mA, respectively.
- The pressure change is converted into a linear motion that moves the linear actuator or a rotary motion that turns the rotary actuator. This movement is communicated to the valve, and the valve repositions itself accordingly.
Types of Valve Positioners:
Pneumatic Positioners – Get pneumatic signals (3–15 psi).
Electro-Pneumatic Positioners – Change 4-20 mA electrical signals to pneumatic output.
Microprocessor-based models called Digital/Smart Positioners Aid in diagnostics, provide remote control, and enable self-calibration.
Key Advantages:
Enhanced valve response time and accuracy
Eliminated process variability
It proves to be an effective friction, hysteresis, or actuator spring wear compensator.
Allows the setting up of split-range and sophisticated flow control systems