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Control Valve Failure Position


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#1 grimster85

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Posted 19 July 2010 - 01:17 AM

I have been looking at a system that claims to be "fail last closed". I have come across this terminology before as has another process engineering collegue. However our instrument engineer, and a valve vendor specialist had never heard of this before.

I have never actually been involved in a valve installation but I had assumed that the positioner would "trap" the air in the valve and that the spring in the actuator would be pushing to close the valve (thus over a long period the valve would eventually close due to leaks)

Does anyone have experience in this area and could provide me with some experience with this type of valve.

Thank you for any help that can be provided.

#2 deltaChe

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Posted 19 July 2010 - 08:22 AM

I have been looking at a system that claims to be "fail last closed". I have come across this terminology before as has another process engineering collegue. However our instrument engineer, and a valve vendor specialist had never heard of this before.

I have never actually been involved in a valve installation but I had assumed that the positioner would "trap" the air in the valve and that the spring in the actuator would be pushing to close the valve (thus over a long period the valve would eventually close due to leaks)

Does anyone have experience in this area and could provide me with some experience with this type of valve.

Thank you for any help that can be provided.



Dear

Base on my limit experiece, failure in last position or "as is" is most easily accomplised with an MOV.
And, these MOV will remain where positioned on loss of electrical power.

#3 chemsac2

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Posted 19 July 2010 - 10:48 AM

grimster85,

Control valves with "Fail last" as fail safe condition can be either FLDC (i.e. fail last drift close) or FLDO (Fail last drift open). Such valves would be locked to their last position on air failure. However, due to leaks they would either go to open position for FLDO or closed position for FLDC.

In fact, even if this is not captured during engineering stage, vendor would ask engineering to confirm if valve is FLDC or FLDO.

Regards,

Sachin




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