Common Fault Analysis and Troubleshooting for Electric Valve Actuators

An electric actuator primarily consists of a power board, main board, travel detection device, torque measurement device, AC contactor or frequency converter, motor, and reducer. An electric actuator uses a small motor to drive a worm gear in a first-stage reduction mechanism, capable of delivering multi-turn, angular, or linear motion to the valve. The actuator's motion output is determined by the characteristics of the valve being controlled.
If the operating torque required by the controlled valve is particularly high, such as greater than 2000 NM, a second-stage reduction gearbox is typically added. The electric actuator directly drives the second-stage reduction gearbox, which in turn drives the valve. Electric actuator protection typically includes valve position protection, torque protection, motor overheat protection, motor stall protection, control unit fault protection, and power failure protection. Troubleshooting should be targeted based on the alarm information provided by the electric actuator.

1. Electric Actuator Valve Position Loss

Battery Power Loss
When using an incremental encoder to measure stroke, the actuator must have a battery as an auxiliary power source. Even if the AC power is lost, the incremental encoder can still detect changes in the electric actuator's valve position, and the fully open and fully closed positions of the electric actuator will not change. However, if the AC power is lost and the battery power is depleted, the incremental encoder will not be able to detect the actual valve position change, resulting in valve position loss. When AC power is restored, some manufacturers' products default to a 50% valve position. Some manufacturers using incremental encoders have improved their hardware by adding a capacitor circuit. This capacitor stores energy to maintain the valve position when the AC power is lost. However, the electric actuator cannot be manually operated without battery power, otherwise the valve position will still be lost. Therefore, it is important to replace the battery promptly when it is low.

Hardware Damage
A broken encoder wire in the electric actuator, low encoder input voltage, damaged travel transmission gears, corrosion on the encoder circuit board, or damage to the mainboard's travel detection and storage components can all cause abnormal valve position changes or loss. When troubleshooting, confirm that the encoder input voltage is normal and then replace the mainboard or travel encoder to eliminate these issues one by one.

2. Electric Actuator Torque Failure

Torque Protection Failure
Measuring the output torque of electric actuators mainly involves mechanical protection switches, torque calculation based on motor current, voltage, and power, and sensor-based protection devices. Mechanical torque protection switches were prevalent before 2000 and were a transitional product. Some low-end electric actuators still use them today. These torque protection switches only provide a switching value for torque protection and cannot provide real-time process torque data, resulting in large measurement errors. Calculating torque using the motor current, voltage, and the phase angle between them requires a software program. Sensor-based torque protection devices combine the axial deformation of the actuator's primary worm gear with a pressure sensor. The voltage output by the pressure sensor is amplified by a circuit board and the signal is input to the control board to obtain the actuator's real-time torque value.
Torque protection failure is primarily manifested by tripping of the actuator's AC power supply, severe wear of the actuator's worm gear, bending of the gate stem, or even broken screws connecting the actuator to the valve. The torque protection value should be reset and verified using a torque calibration bench. When selecting valve torque, it's crucial to ensure the actuator can reliably open and close the valve while also ensuring the electric actuator torque does not exceed the maximum torque the valve stem can withstand. This presents some challenges in parameter setting, as the maximum torque that each valve stem can withstand is often difficult to determine. Electric actuator manufacturers often set torque parameters based on experience, initially setting a low torque protection value. If the torque protection triggers, the torque protection value is increased appropriately until the valve can open and close normally in the cold state. If the torque protection triggers in the hot state, the torque protection value is further increased to ensure normal opening and closing in the hot state.

Torque Protection Malfunction
When the electric actuator is manually operated lightly, the over-torque protection triggers. After eliminating the possibility that the torque protection value is set too low, for intelligent electric actuators, observe the torque value displayed on the LCD screen or the indicator light indicating over-torque. Rotate in the opposite direction, and the over-torque signal should disappear. Otherwise, replace the mainboard or torque detection device to correct the problem. For mechanical torque detection devices, rotate the motor actuator in the opposite direction to check if the torque switch is disconnected. If not, replace the torque protection switch. If overtorque still occurs even after the torque protection switch is set to the maximum value, consider whether the electric actuator's torque is too low.

3. Specific Causes of the Electric Actuator Motor Rotating but the Actuator Output Shaft Not Rotating

The electric actuator is engaged on the manual side. After the electric actuator motor rotates, the switching device fails to engage on the motor side, causing the motor to idle.
The worm gear driven by the electric actuator is worn and slipping, causing the motor to idle and the actuator output shaft to not rotate.
One of the three phases of the motor power cable has loose contact, causing the motor to intermittently rotate.
If the electric actuator motor is idling, after confirming that the power supply is not faulty, open the electric actuator's primary worm gearbox and inspect the worm gear for wear. If wear is severe, return the actuator to the factory for repair or replace it with a new one. A faulty switching device can usually be repaired on-site, depending on the operating principle of the switching device of the different electric actuators.

4. Causes of Electric Actuator Motor Overheating

Frequent operation of the electric actuator can cause the motor to overheat, triggering protective action.
A broken wire or poor contact in the RTD temperature sensor terminals can cause a false overheat signal.
A damaged motor rotor bearing prevents rotation, leading to motor stalling and overheating.
If the motor bearing is damaged, the bearing should be replaced; if the temperature sensor is damaged, the motor should be replaced. Replacing the temperature sensor alone requires disassembling the stator winding, which is prohibitively expensive, potentially costing the equivalent of purchasing a new motor with hundreds of watts of power.

5. Causes of Electric Actuator Inoperability

A power board failure. The power board provides control power to the main board. A power board failure can prevent both local and remote operation.
A main board failure can prevent control commands from being executed.
A power supply failure causes the electric device to detect a phase loss or no power, preventing the electric actuator from operating.
For this type of failure, the only option is to replace the main board and power board, one by one, as testing of the circuit boards is generally not possible in the operating environment.

6. Reasons for the electric actuator not providing full open/close feedback

The terminal position relay is faulty and cannot reliably close or open.
The relay is incorrectly set.
The mainboard is faulty.
When troubleshooting, first check the terminal position settings to ensure they are correct. For relay failure, if the position relay is installed independently, replace the relay. If the position relay is welded to the mainboard, replace the mainboard.