A Guide to Diagnosing and Solving Problems with Control Valve Oscillations and Uneven Opening

1. Description of the problem and relevance

This guide is dedicated to diagnosing and solving problems with oscillations and irregular opening of the control valve in industrial systems. Protected criticality level: critical. The violation affects boosters, operating valves, control systems, and related actuators. Improper adjustment, insufficient actuator size, dryness or process influences can cause unpredictable valve oscillations.

2. Safety net

Warning: It is forbidden to carry out diagnostics without disconnecting the power and blocking the mechanism.

Use isolation means and connect to the system with PPE (personal protective equipment). Before diagnosis, turn off the power and perform a signature lock. Measure system pressure and cut off power if higher than 0.5 bar.

3. Necessary diagnostic tools

4. The first review checklist

5. Systematic diagram of diagnostics

1. Determine the type of oscillation: low-frequency (0-10 Hz), medium-frequency (10-100 Hz), high-frequency (100-1000 Hz).
2. Measure the valve vibration with the analyzer. If the vibration exceeds 4.5 mm/s, note.
3. Check the settings of the amplifier: measure the voltage at the input and output ends.
4. Measure the voltage on the drive motor. If it fluctuates by 10% from the nominal during operation, mark it.
5. Measure the temperature of the valve. If it exceeds 60°C, note.
6. Measure the drive forces. If the force is higher than 80% of the nominal, note.
7. If the vibration is greater than 4.5 mm/s, continue with the diagnosis.
8. Check for micro-breaks on the valve surface.
9. Measure the temperature around the valve.
10. If the measured temperature is higher than 60°C, note.
11. Check if there are changes in the system in the last 30 days.
12. Measure the valve vibration again.
13. If the measured vibration is greater than 4.5 mm/s, continue with the diagnosis.
14. Measure the drive forces.
15. If the force is higher than 80% of the nominal, note.
16. Perform amplifier tuning diagnostics.
17. Measure valve vibration.
18. If the measured vibration is greater than 4.5 mm/s, note.
19. Measure the temperature of the valve.
20. If the measured temperature is higher than 60°C, note.

6. Matrix of causes of exceptions

7. Root cause analysis for each fault

7.1. Incorrect positioner setting

A positioner, if not configured correctly, cannot accurately control the valve position. This may result in hesitation and uneven opening. To check the positioner setting, use a multimeter and check the voltage at the input and output. If the voltage is not within specifications, this confirms the cause. Incorrect adjustment can damage the valve and reduce control accuracy.

7.2. Insufficient drive size

An actuator that is too small for a given flow cannot operate the valve effectively. This results in hesitation and uneven opening. To check the drive size, use a dynamometer and measure the force. If the force is less than 80% of the nominal strength, this confirms the cause. Undersizing the drive can result in drive damage and reduced efficiency.

7.3. Valve dryness

Valve dryness leads to increased friction and decreased control accuracy. This may cause vibrations and uneven opening. To check whether the valve is dry, use a thermal chamber and measure the temperature. If the temperature is above 60°C, this confirms the cause. Valve dryness can cause valve damage and reduced performance.

7.4. Process injections

Process disturbances, such as changes in pressure or temperature, can cause fluctuations in the system. To check process injections, use a pressure meter and measure the pressure. If the pressure fluctuates, this confirms the cause. Process leaks can damage the valve and reduce accuracy.

7.5. Oscillation frequency mismatch

A mismatch in the oscillation frequency can lead to resonance and oscillation in the system. To check the vibration frequency, use a vibration analyzer and measure the frequency. If the frequency does not match the vibration frequency, this confirms the reason. A mismatch in oscillation frequency can damage the system and reduce accuracy.

8. Step-by-step troubleshooting procedures

8.1. Incorrect positioner setting

1. Turn on the power to the positioner.
2. Use a multimeter to check the voltage at the input and output.
3. Compare measured values ​​with specifications.
4. If the voltage is not within specifications, adjust the positioner.
5. Check the positioner settings again.
6. Turn on the power and check the operation of the valve.
7. If the vibrations disappear, the procedure is completed.

8.2. Insufficient drive size

1. Turn on the drive power.
2. Use a dynamometer to measure force.
3. Compare measured values ​​with nominal values.
4. If the force is less than 80% of the rated force, replace the drive.
5. Check the drive size again.
6. Turn on the power and check the operation of the valve.
7. If the vibrations disappear, the procedure is completed.

8.3. Valve dryness

1. Turn on power to the valve.
2. Use a thermal camera to measure temperature.
3. Compare the measured values ​​with the standard values.
4. If the temperature is above 60°C, check the cooling system.
5. Check for leaks.
6. If leaks are found, replace the seals.
7. Check valve operation.
8. If the vibrations disappear, the procedure is completed.

8.4. Process injections

1. Power on the system.
2. Use a pressure meter to check your pressure.
3. Compare the measured values ​​with the standard values.
4. If the pressure fluctuates, check the system.
5. Check for leaks.
6. If leaks are found, replace the seals.
7. Check valve operation.
8. If the vibrations disappear, the procedure is completed.

8.5. Oscillation frequency mismatch

1. Power on the system.
2. Use a vibration analyzer to check the frequency.
3. Compare the measured values ​​with the standard values.
4. If the frequency does not match the vibration frequency, check the system.
5. Check for resonance.
6. If resonance is detected, change the system settings.
7. Check valve operation.
8. If the vibrations disappear, the procedure is completed.

9. Preventive visits

10. Spare parts and components

Go to the UNITEC-D catalog to purchase spare parts.

11. Reference books

• DSTU 2245: Production Measurement and Control
• EN 13445: Validity and requirements for industrial valves
• ISO 9001: Quality management systems
• CE, UkrSEPRO certification
• Original technical documents of the manufacturer
• UNITEC-D additional guides