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Analysis of Common Causes of Valve Positioner Problems
Release time:
2026-04-07 15:22
To troubleshoot a valve positioner, it is essential to accurately identify which stage or component of the device has failed. Typically, two fault-analysis approaches are employed: first, based on the valve positioner’s transfer function, the system can be analyzed stage by stage and component by component; this method is less suitable for on-site maintenance but highly effective for diagnosing complex and difficult-to-resolve problems. Second, maintenance personnel can conduct a comprehensive analysis and judgment based on the observed symptoms of the fault; this approach is most appropriate for field troubleshooting. The following section outlines the root causes of common faults that may occur in valve positioners:
1. The valve positioner has signal input but no output pressure signal.
(1) Electrical/pneumatic positioner: Foreign matter is present between the armature and the coil frame.
(2) Blockage of the constant orifice.
(3) Poor alignment or damage to the nozzle baffle.
(4) The diaphragm in the amplifier (either a metal diaphragm or a rubber diaphragm) is damaged.
(5) Incorrect gas line connections (including the amplifier).
(6) The positive and negative terminals of the electrical/pneumatic positioner’s input signal cable are reversed.
(7) The diode in the input terminal box of the positioner is open-circuited, or the wiring is poor.
(8) The air supply pressure does not meet the requirements.
(9) The amplifier’s air consumption exceeds the rated value by a large margin.
(10) The magnetic polarity of the electric/pneumatic positioner is installed incorrectly.
(11) Excessive preloading force on the amplifier.
(12) The spool in the spool-type amplifier is jammed by a foreign object.
(13) The “manual/automatic” switch is in the wrong position (neither manual nor automatic).
(14) Short circuit in the electrical signal input to the electric/pneumatic positioner.
(15) The balance spring was improperly installed and adjusted.
2. The output pressure of the lower-stroke positioner changes slowly.
(1) The gas-cone valve of the amplifier has a small cone angle.
(2) Long-term use of the amplifier diaphragm can lead to elastic hysteresis.
(3) The sensing element of the pneumatic positioner (bellows or diaphragm chamber) exhibits elastic hysteresis after prolonged use.
(4) The feedback spring exhibits elastic hysteresis.
3. The upper stroke limiter indicates a slow pressure change.
(1) The amplifier’s intake ball valve is stuck too far down.
(2) The amplifier has a relatively high air consumption.
(3) The amplifier’s intake ball valve is contaminated, reducing the flow area.
(4) The ratio of the diameter of the constant throttling orifice to the nozzle diameter is less than the rated value (the value specified in the technical requirements).
(5) Poor fit between the nozzle and the baffle.
(6) There is slight friction between the armature and the coil holder.
2020-01-19
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