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Fail Open Scenario - Two Paralell Control Valves


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#1 J_Leo

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Posted 12 December 2021 - 05:03 PM

Hello Fellow Engineers,

 

Under what circumstances on the control scheme can two parallel pressure control valves be considered independent, so only the bigger one needs to be considered for sizing of PSV for the control valve fail open scenario?

 

Currently, two control valves fail simultaneously is considered for the downstream PSV sizing. If I increase the Cv of the smaller control valve, the relieving load would exceed the PSV capacity. I am wondering if it is possible to size the PSV based on the Cv of one control valve but just not sure about the criteria to make them independent.

 

Thanks,

Leo 



#2 Bobby Strain

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Posted 12 December 2021 - 06:56 PM

I don't see a way to make them independent. You might evaluate using separate pressure transmitters and pressure controllers.

And even with that, you need to assess the risks if both valves fail open.

 

Bobby



#3 fallah

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Posted 13 December 2021 - 02:15 AM

 

Under what circumstances on the control scheme can two parallel pressure control valves be considered independent, so only the bigger one needs to be considered for sizing of PSV for the control valve fail open scenario?

 

Currently, two control valves fail simultaneously is considered for the downstream PSV sizing. If I increase the Cv of the smaller control valve, the relieving load would exceed the PSV capacity. I am wondering if it is possible to size the PSV based on the Cv of one control valve but just not sure about the criteria to make them independent.

 

 

Hi,

 

To get a proper response, please upload a simple sketch of the system you described...



#4 latexman

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Posted 13 December 2021 - 07:29 AM

Is there any common cause failure?



#5 J_Leo

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Posted 16 December 2021 - 01:54 PM

Thank all for your responses.

 

I will prepare a sketch and have it uploaded.



#6 astro

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Posted 17 May 2022 - 10:42 AM

I'd suggest that my comments over at Double Jeopardy? Post #9, could provide some useful points to consider.






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