Solutions for Electric Control Valve Malfunctions

Electric control valves are essential components in automated control systems, widely used in industrial processes to regulate fluid flow, pressure, and temperature precisely. However, when an electric control valve fails to respond to control signals, it can lead to system interruptions or reduced efficiency. Such faults are often caused by electrical, mechanical, or circuit issues, requiring a systematic troubleshooting approach to identify and fix the problem. This article will outline common causes and troubleshooting steps to help users quickly diagnose and resolve issues, ensuring the electric control valve returns to normal operation.

Check the Circuit Connections

Start by checking the connections in the power supply circuit, signal circuit, and valve position feedback circuit to ensure they are functioning properly. Loose or faulty connections can cause the valve to fail. The steps are as follows.

Power Supply Circuit: Verify that the power is on, the voltage is stable, and there are no breaks, looseness, or damage in the supply cable.
Signal Circuit: Ensure that the control signal wiring is correct and undamaged. If using an analog signal, confirm that the signal source is providing the correct current or voltage.
Valve Position Feedback Circuit: Check that the feedback sensor is properly connected and returning the correct signal.
Also, check if the limit switch has reached its set point or if there is any malfunction. A mechanical or electrical failure in the limit switch could prevent the valve from functioning as expected.

Check Mechanical Components

Mechanical faults in the electric control valve can also lead to non-responsiveness. Check the following mechanical parts.

Valve Sticking: Verify if external resistance or internal jamming is preventing the valve from moving. You can try manually operating the valve to see if it moves smoothly.
Actuator: Check for any mechanical issues like jams or damage in the actuator's components (e.g., gears or levers).
Manual Mode Check: If the valve operates normally in manual mode, most electrical faults can be ruled out, allowing you to narrow down the problem.

Further Checks in Manual Mode

If the valve works in manual mode, the issue is likely in the control circuit. Disconnect one of the control signal wires and input a current signal directly into the actuator's analog signal input. Observe whether the valve responds to the signal. If the actuator responds, the issue may be with other components of the control circuit, such as the circuit board, sensor, or control signal source.

Input Signal Check

If the valve is not responding to control signals, check the resistance at the control board's input. Follow these steps:

Use a multimeter to measure the resistance at the analog input, confirming it is within the normal range. For current-input actuators, the resistance should generally be below 500Ω, while for switch-type actuators, the input resistance is usually above 1kΩ.
If the input signal's resistance is normal but the valve still doesn't respond, the issue may lie in the control circuit's board. In this case, replacing the circuit board or inspecting its control signal detection components is recommended.

Actuator Power and Internal Faults

If the electric control valve suddenly stops responding, perform detailed checks on the following components.

Actuator Power Tripping: Verify whether the actuator power has tripped, possibly due to a short circuit in the actuator's internal heater. Use a multimeter to check for a short circuit in the heater.
Servo Control Board Fuse: Check if the fuse on the servo control board has blown. If so, replace the fuse.
AC Contactor Damage: The internal AC contactor in the actuator may be damaged, preventing the motor from starting. After turning off the power, open the actuator to inspect the coil resistance and contact connections. If the contacts are not functioning, replace the contactor.

Motor Overheating Fault Analysis

Motor overheating can also cause the valve to fail to respond. Overheating usually occurs when the motor's thermal protection device is triggered to cut off the power to prevent damage. The actuator may resume normal operation once the motor cools down. Check the following:

Excessive Start-ups: Frequent motor starts can lead to overheating. Check if the start frequency is set too high.
Incorrect Dead Zone or Inertia Settings: If dead zone or inertia constants are set improperly, they can also cause overheating.
Motor Fault Diagnosis: If the motor seems faulty, measure the resistance of the motor windings with a multimeter. Open or short circuits in the windings indicate a faulty motor that needs replacing.

Actuator Calibration

Some intelligent electric actuators require calibration before their first use. The calibration process includes:

Setting the actuator's direction of rotation.
Adjusting the valve's stroke.
Fine-tuning the dead zone and inertia constants.
If the actuator hasn't been calibrated, it may fail to operate as expected. Restart the calibration process and ensure all parameters are set correctly. After recalibration, the actuator should respond to control signals properly.

Conclusion

Troubleshooting an electric control valve not responding involves examining multiple areas, including electrical, circuit, and mechanical components. By systematically checking the power supply, signal circuits, valve position feedback, actuator, and motor, you can effectively identify the cause of the problem. Most faults can be resolved through careful inspection and repair of the actuator and control circuit, ensuring the electric control valve returns to normal operation.