How to Troubleshoot Control valve

In this article, you will find how you can troubleshoot problems Control valve with each problem and its solutions.

Introduction

I hope you liked our previous articles on maintenance jobs on various field instruments. Today we will see the maintenance jobs on the control valve.

So, let us start with this article.

NOTE: In this case, we will see air to open valve also known as air fail close valve. For maintenance jobs on air to close valves, opposite actions are to be considered.

Problem> Control valve not opening/stuck at close position.

Solutions:

1. The control valve can be in a locked position using the handwheel. Remove the handwheel’s latching and make it free.
2. Check the instrument air supply in the positioner’s inlet. Set it as per the instrument air supply required. The value can be seen in the nameplate as well as the datasheet.
3. If instrument air is not present downstream of SOV (if SOV is present), then check the SOV. SOV might not be working. Check the SOV. If found faulty, then replace it or service it.
4. Power supply to the SOV can be absent. Check the whole loop for knowing and attending to the issue of voltage absence on SOV.
5. Check the actuator. If it is passing, then replace it or overhaul it.
6. Check whether the positioner is in power on condition or not. If the positioner is not in power on condition, then check for the voltage by checking the loop.
7. If the air supply to the positioner is ok, then check the command on the positioner. If the command is not as per the command given by the PLC/DCS, then check the whole loop (terminations, cable, barrier).
8. If there is no signal to open the control valve, then in the worst case, the analog output channel can become faulty. Change the channel and do the necessary configurations.
9. The valve positioner can be in manual mode. Put it in auto mode.
10. If all the above-mentioned problems are not found, then the valve might be stuck. If a handwheel is available, then try opening using the handwheel. If it works then do rousing and then try opening using air. If it does not open then drop the valve and do repairing.

Problem> Control valve not opening fully and getting stuck in between

Solutions:

1. Check the instrument air supply in the positioner’s inlet. Set it as per the instrument air supply required. The value can be seen in the nameplate as well as the datasheet.
2. Check the instrument air tubing for leakage. If any tube leakage is there then attend the leakage.
3. Check the actuator. If it is passing, then replace it or overhaul it.
4. If the actuator is found ok, then check the condition of the SOV. The SOV might be passing.  Service it.
5. Check the condition of the limit stop bolt in the actuator and/or gearbox. They can be in such a position which does not allow the actuator to open fully.
6. The valve might be stuck. If the handwheel is available, then try opening using the handwheel. If it works then do rousing and then try opening using air. If it does not open then drop the valve and do an overhauling.

Problem> Control valve not opening fully and getting stuck in between

Solutions:

1. The control valve can be in a locked position using a handwheel. Remove the handwheel’s latching and make it free.
2. Check the instrument air supply in the positioner’s inlet. Set it as per the instrument air supply required. The value can be seen in the nameplate as well as the datasheet.
3. Check the feedback assembly of the positioner. If it is having an issue, then attend it.
4. Do calibration of the control valve and do stroke checking.
5. If instrument air is not present in downstream of SOV (if SOV is present), then check the SOV. SOV might not be working. Check the SOV. If found faulty, then replace it or service it.
6. Power supply to the SOV can be absent. Check the whole loop for knowing and attending to the issue of voltage absence on SOV.
7. Check the actuator. If it is passing, then replace it or overhaul it.
8. Check whether the positioner is in power on condition or not. If the positioner is not in power on condition, then check for the voltage by checking the loop.
9. If the air supply to the positioner is ok, then check the command on the positioner. If the command is not as per the command given by the PLC/DCS, then check the whole loop (terminations, cable, barrier).
10. The valve positioner can be in manual mode. Put it in auto mode.
11. If all the above-mentioned problems are not found, then the valve might be stuck. If a handwheel is available, then try opening using the handwheel. If it works then do rousing and then try opening using air. If it does not open then drop the valve and do an overhauling.

Problem> Control valve having hunting issue

Solutions:

1. Check the instrument air supply in the positioner’s inlet. Set it as per the instrument air supply required. The value can be seen in the nameplate as well as the datasheet.
2. Check the instrument air supply pressure. It should be constant.
3. Check all the connections. A loose connection can cause this problem.
4. Do calibration of the control valve and do stroke checking.
5. Check the feedback assembly of the positioner. If it is having an issue, then attend to it.
6. Check the actuator. If it is passing, then replace it or overhaul it.

Resources

I found this interesting free Engineering book on Control Valve by Fisher(Emerson)Fifth Edition.

CONTROL VALVE HANDBOOK

Download Here

EndNote

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