We have IL make Control Valve in VHP(100 Kg/cm2) to HP (40 Kg/cm2) PRDS line. Suppose it is opening at 51% with the command at constant load.

Suddenly valve closes at command 51% and again after few seconds open and follow the commands. Valve accessories are positioner, volume booster, and Air Lock relay. Can anyone tell why valve suddenly becomes closed?

With regards
Sanjib dutta

 

Sanjib,

You simply have not provided enough information for the people on this mailing list to efficiently help you. This is common problem that people, who are many time engineers, expect that they can spend a minimum effort in stating their problem on this mailing list (and other forums), while getting a maximum effort by this mailing list in solving their problem. This results in the people on this mailing list being forced to speculate on potential solutions, many times wasting their good time in a Good Samaritan effort.

Some of the information you could have provided that would help out are:

1. Please do not use acronyms like "IL," VPH," "HP," & "PRDS" in your problem statement as people on this mail list may not recognize the acronyms or the acronyms letters may mean different things to different people.

2. What have you done to troubleshoot the problem so far?

3. Is this a new problem, e.g. has it happened before on this loop?

4. Has this happened to any of the other of the control loops in the system?

5. If this is a new problem, has there been any recent changes to the loop? To the control system?

6. What kind of signal is being used from the control system to the valve positioner? 4-20 mA, HART, Fieldbus?

7. What was the signal from the control system doing at this time?

8. How many times has this happened?

9. If more than once, what time of the day/week has the problem occurred?

10. Were there any other unusual operation of the control loops in the same unit operation at the same time as this problem?

11. Are there any override controls on this loop?

12. What kind of valve are you talking about? Manufacturer/Model

13. What are the manufacturers/models of the associated equipment?

14. Did you have any power problems when this occurred? Alarms?

15. Was lightning occurring during this time?

16. Is the air supply to the positioner clean?

17. Is your positioner subject to vibrations?

18. Did the process reflect a change when the valve went from 51% to 0% and then back to 51%, e.g. change in flow, pressure, etc.?

19. Were there any unusual process conditions or operations prior to this happening?

20. Did you have any unusual alarms during the time that this occurred?

21. Is your positioner a smart one that could help you troubleshoot this problem?

When stating a problem to request someone's assistance always follow the Golden Rule of Communication - "Always state or provide information to someone else like you would like it stated to you."

William (Bill) L. Mostia, Jr. PE
ISA Fellow, SIS-TECH Fellow,
FS Eng. (TUV Rheinland)
SIS-TECH Solutions, LP
713-909-2139 (o)


"No trees were killed to
send this message, but a large number of electrons were terribly
inconvenienced." Neil deGrasse Tyson

Any information is provided on a Caveat Emptor basis.

 

Is it actually closing, or is it just the feedback says it's closing?

One thing you might want to look at is intermittent air pressure loss.
Depending on the type of valve actuator there is a limit sometimes on a
minimum pressure where it will stay open at all, and if you have an
intermittent low pressure , it could close during that time period.