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Valve positioners, classified by structure into pneumatic valve positioners, electro-pneumatic valve positioners, and intelligent valve positioners, are essential accessories for control valves. They are typically used in conjunction with pneumatic control valves; they receive the output signal from the controller and use this signal to control the pneumatic control valve. When the control valve moves, the displacement of the valve stem is fed back to the valve positioner through mechanical mechanisms, and the valve’s position is transmitted to the higher-level system via electrical signals. However, when using valve positioners, various faults may occasionally occur, or there might be different issues with the positioners, and we can provide solutions for those problems. Next, we will introduce some of the problems that may arise when using positioners. Common Troubleshooting for Valve Positioners (I) 1. The valve positioner does not respond to input signals. (1) Check the supply pressure level. The leverage must be at least 1.4 kgf/cm2. For the springreturn actuator type, the supply pressure level must be greater than the spring specification. (2) Check whether the input signal is correctly supplied to the positioner. The signal should be 4~20mA. (3) Check whether the zero point or span point is set correctly. (4) Check whether the nozzle of the valve positioner is blocked. Additionally, check whether pressure is being supplied properly to the valve positioner; the pressure is discharged through the nozzle. If the nozzle is clogged by any substance, please send the product for repair. (5) Check whether the feedback rod is installed correctly. 2. The pressure at OUT1 reaches the exhaust pressure level and will not decrease any further. (1) Check the A/M switch. If the switch is damaged, replace the switch or the pilot relay valve. (2) Check for any gaps or damage between the nozzle and the baffle. If it is damaged, please send the product to YTC for repair. 3. Pressure is depleted only by the A/M switch. (1) Check whether the nozzle of the valve positioner is clogged. Additionally, check whether pressure is being supplied properly to the valve positioner; the pressure is discharged through the nozzle. If the nozzle is clogged by any substance, please send the product to the manufacturer for repair. 4. Deviation occurs. (1) Check whether the safety spring has shifted. (Next to the Pilot solenoid valve) (2) Check whether the size of the actuator is too small. If that is the case, insert a hole to reduce pressure flow. (3) Check for friction between the valve and the actuator. If that is the case, increase the size of the actuator or reduce the friction level. Common Troubleshooting for Valve Positioners (II) 1. The actuator only operates in open/close mode. (1) Check the operation type of the actuator and valve positioner. The air pressure discharged from port OUT1 causes the input signal level to increase. Therefore, the connection is the OUT1 port when using a single actuator as standard. Ensure that the range adjustment is correct according to the valve system settings. 2. The linearity is too low. (1) Check whether the valve positioner is properly positioned. Specifically check whether the feedback rod is properly parallel to the 50% point of the ground. (2) Check whether the zero point and range points have been correctly adjusted. If one of the values is adjusted, the other must also be adjusted again. (3) Check whether the supply air pressure level of the regulator is stable. If the level is unstable, the regulator must be replaced. 3. The valve positioner has too low hysteresis. (1) If it is a double-acting actuator, please check whether the seat adjustment is being performed correctly. For any further inquiries regarding seating, please contact the manufacturer for adjustments. (2) Gear backlash may occur when the feedback rod and lever spring are loose. Avoid back binding; adjust the lever spring. (3) Check whether the connecting rod of the feedback rod is tightened.