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What role does a valve positioner play in control valve regulation?
Release time:
2026-04-07 15:22
Valve positioners are classified, according to their structure, into pneumatic valve positioners, electro-pneumatic valve positioners, and smart valve positioners. They are essential accessories for control valves and are typically used in conjunction with pneumatic control valves. A valve positioner receives the output signal from the controller and uses this signal to regulate the pneumatic control valve. Once the control valve actuates, the displacement of the valve stem is fed back to the valve positioner via a mechanical linkage.
The specific functions of a valve positioner in control valve regulation are as follows:
1. Used in critical control systems with stringent control-quality requirements to enhance the positioning accuracy and reliability of control valves.
2. Used in applications where the pressure differential across the valve is large (Δp > 1 MPa). By increasing the supply air pressure, the actuator’s output force is enhanced to overcome the unbalanced force exerted by the fluid on the valve plug, thereby reducing stroke error.
3. When the controlled medium is high-temperature, high-pressure, cryogenic, toxic, flammable, or explosive, the packing is often tightened significantly to prevent external leakage, resulting in substantial friction between the valve stem and the packing. In such cases, a positioner can help overcome the time delay.
4. When the medium being controlled is a viscous fluid that may contain solid suspended particles, a positioner can overcome the resistance exerted by the medium on the valve stem movement.
5. Use a control valve with a large nominal diameter (Dg > 100 mm) to increase the output thrust of the actuator.
6. When the distance between the regulator and the actuator exceeds 60 meters, a positioner can compensate for the lag in control-signal transmission and improve the valve’s response speed.
7. Used to improve the flow characteristics of control valves.
8. When a single controller is used to implement staged control over two actuators, two positioners can be employed, each receiving the low-range and high-range input signals, respectively. In this configuration, one actuator operates in the low-range mode while the other operates in the high-range mode, thereby realizing staged regulation.
2020-01-19
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