Control valve troubleshooting
The failure of the control valve may lead to a production Loss if there is no alternative bypass line. And manual bypass will be difficult to control the process in such a situation. So control value troubleshooting is very essential to identify the problem. If you’re aware of the possibility of the problem then you can able to solve it in a short time. Some of the common problems that arise in control valves are discussed below.
- Valve not operating
- Valve hunting
- Valve not operating linearly
- Slow response
Value not operating
If the control valve not responding, check the following condition.
1. Whether the air supply is normal.
2.The positioner power supply is normal or not.
3.Check the air filter regulator working condition.
4.Check the volume booster, airlock relay and solenoid value condition if installed additionally.
5.Check all the tube line free from the choke.
6. Check the i /p converter working condition.
7.Check the output of the positioner.
If the output is not coming, service the positioner and calibrate it. If all the above possibility not exists, then the problem will be in the actuator or valve body side.
1.Most of the control value provides a port to check diaphragm damage, the air will get passed through it.
2.Operate the valve manually to release the jammed condition.
3.Remove the actuator stem and valve stem coupling and check the actuator operation to conclude where the problem lies.
If the actuator is not normal, remove the cap and inspect the plate, spring and other parts inside the control value.
By the way, remove the valve body and inspect the condition of all internal parts. And replace it if any damage is available.
Valve Hunting
Valve hunting is one of the common problems that arise in the control valve. The hunting will lead to the disturbance of process parameter like pressure, flow. The abnormality reduces the process efficiency hence it needs to be eliminated immediately.
*Check for any leakage along the tube line in the control valve. Which will make the valve operation abnormal.
*check the position transmitter and the feedback link condition attached to it.
*check the positioner output,in smart positioner we can adjust the bandwidth setting to reduce the hunting.
*Adjust the PID controller tuning will Eliminate this problem.
The problem will solved by above steps. Even if the problem exist check the remaining steps followed for valve not operating condition.
Value not operating linearly
The control valve has to operate linearly for the given command to maintain the process control. An irregular movement of the valve stem leads to a mess in the controller output. The possible causes are mentioned below.
*The position transmitter link may be loosened or removed. Which lead to the wrong input of feedback into the positioner.
*The positioner needs to be calibrated may solve this problem.
*Calibrate the i/p converter even the problem is not solved replace it.
These are some of the problem faced in the control valve. These steps may useful for troubleshooting the control valve. Leave a comment on another problem you have faced in your experience.
