5 replies to this topic

[J_Leo]

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 

[Bobby Strain]

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

[fallah]

 

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...

[latexman]

Is there any common cause failure?

[J_Leo]

Thank all for your responses.

 

I will prepare a sketch and have it uploaded.

[astro]

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