Introduction The new integral electric actuator accepts the standard 4–20 mA signal and automatically modulates butterfly valves, control valves, dampers and the like — no servo amplifier needed — running in automatic, soft-manual or hard-manual states, with status interlocks, high reliability, long life and easy maintenance. Because actuators work in harsh conditions and the regulating element touches the medium directly — heat, pressure, corrosion, wear — faults still occur in service.
Faults divide into electrical and mechanical. The general fault-finding method: first switch the actuator to HARD-MANUAL (direct hand command) and see whether it executes correctly. If hard-manual works, switch to SOFT-MANUAL (4–20 mA input) and check; if hard-manual fails, check the electrical control section and whether the regulating element is jammed.
1.1.1 Motor circuit 1) Larger actuators use three-phase motors. In harsh, frequently cycling service, contactor contacts burn and make poorly, causing phase-loss overheating or failure to run in one direction — inspect contactors carefully during maintenance. 2) Smaller actuators use single-phase motors switched by solid-state relays; typical faults are a degraded start capacitor or a burned SSR causing failure to run or one-direction failure.
1.1.2 Control modules The new integral actuator concentrates control in the main control module, position-transmitter module and power module. The transmitter and power modules are easy to check with a multimeter (feedback signal, output voltages). The main module is verified by substitution with a spare or on a healthy unit. Modules themselves rarely fail; the common fault is loose, broken or floating wiring due to vibration or installation — e.g. a transmitter module hit by high voltage or with a failed weak component gives a wrong feedback signal, abnormal indication and loss of automatic control. Install and maintain carefully; keep module wiring solid.
1.1.3 Potentiometer and travel control These connect to the rotating parts and often fail through poor connection. A loose potentiometer coupling makes the transmitter output unrepresentative of actual position and the actuator uncontrollable; a badly coupled travel mechanism fails to protect and the machinery suffers mechanical damage.
1.1.4 Signal interference The 4–20 mA control signal is easily disturbed — the actuator hunts and never settles. Screen the signal cables properly and route them away from strong interference sources.
Install and commission strictly per the manual — above all set the travel limits so the valve neither over-closes nor over-opens and jams. In service, process conditions — excessive differential pressure, corrosion and wear — can jam the valve, overheating the motor or tripping protection. To judge: disconnect power and try the valve by hand. If the actuator works but cannot modulate the medium, the actuator-valve coupling has likely come loose or the valve itself is faulty.
