(1) Used in critical control systems where high control quality is required, to enhance the positioning accuracy and reliability of the control valve.
(2) Used in applications where there is a significant pressure differential across the valve (△p > 1 MPa). By increasing the air supply pressure to boost the actuator's output force, the system can overcome the unbalanced forces exerted by the fluid on the valve plug and minimize stroke errors.
(3) When the controlled medium is high-temperature, high-pressure, cryogenic, toxic, flammable, or explosive, the packing is often compressed tightly to prevent external leakage; consequently, the friction between the valve stem and the packing is substantial. In such cases, a positioner can be used to overcome control lag.
(4) When the controlled medium is a viscous fluid or contains suspended solids, a positioner can be used to overcome the resistance exerted by the medium against the movement of the valve stem.
(5) Used with large-diameter control valves (DN > 100 mm) to increase the thrust output of the actuator.
(6) When the distance between the controller and the actuator exceeds 60 meters, a positioner can be used to overcome transmission lag in the control signal and improve the valve's response speed.
(7) Used to improve the flow characteristics of the control valve.
(8) When a single controller is used to manage two actuators for split-range control, two positioners can be employed-one configured to accept low-range input signals and the other high-range input signals-such that one actuator operates within the lower range and the other within the upper range, thereby establishing a split-range control scheme.
