6 replies to this topic

[J_Leo]

Dear Fellow Engineers,

 

We have a PSV with a control valve fail open scenario. The control valve installed at the site is a Flowserve Mark One valve, Veltek series.

The engineering contractor used the equations from Flowserve application manual for Vogt series.

 

The problem is the result from the engineering contractor using Flowserve equations is much larger than the ones I used to check their results (about 30% more). If we use their results, the set pressure of the PSV has to be increased to handle the increased relief rate.

 

Please give advice what to do with this situation.

 

The equations from Flowserve and the ones I used are attached for our reference.

 

Thank you in advance for your help.

 

 

Attached Files

•  flow rate using Cv.pdf   397.72KB   67 downloads

Edited by J_Leo, 20 September 2018 - 01:37 PM.

[fallah]

 

The equations from Flowserve and the ones I used are attached for our reference.

 

 

Nothing attached...!

[fallah]

Dear Fellow Engineers,

 

We have a PSV with a control valve fail open scenario. The control valve installed at the site is a Flowserve Mark One valve, Veltek series.

The engineering contractor used the equations from Flowserve application manual for Vogt series.

 

The problem is the result from the engineering contractor using Flowserve equations is much larger than the ones I used to check their results (about 30% more). If we use their results, the set pressure of the PSV has to be increased to handle the increased relief rate.

 

Please give advice what to do with this situation.

 

The equations from Flowserve and the ones I used are attached for our reference.

 

Thank you in advance for your help.

 

J_Leo,

 

No response for uploading attachments...

 

Anyway, IMO the result from the Flowserve equation used by Engineering Contractor could be much closer to the actual result than the one you use; and on the other hand for the existing PSV you might mostly cannot increase the set pressure beyond a little value...

 

Hence, you can check the result of Engineering Contractor with the vendor of control valve to ensure getting right value for PSV relief load...and for additional relief you can ask vendor to use a facility, say mechanical stop, to limit the flow passing through the valve in full open position...

Edited by fallah, 20 September 2018 - 10:22 AM.

[Bobby Strain]

So, why would you need to raise the set pressure? The relieving pressure can exceed the design pressure by 10% in this case.
But, yes, it's best to double check your contractor calculations. Is this stream two-phase or flashing liquid? That makes the calculation more difficult. If it's single phase, that should not be a problem with calculations. If you dictate capacity design to the contractor, then you are giving taking on a liability to your company.

 

And you probably know that some companies require that the flow is based on an open control valve bypass in addition to what passes the control valve.

 

Bobby

[J_Leo]

Hi Fallah and Bobby,

 

The missing file is attached. The relief is gas only, not two-phase. I will explain a little more later.

 

Thanks,

Leo

[Bobby Strain]

Leo,

       You can find CV for your valve at the Flowserve site. So, why not use them?

http://instrumentati...lection-manual/

 

Bobby

[J_Leo]

Bobby,

 

Thank you. I am setting up the calculations using the equations on the website you provided. Let me see what happens. 

I also called Flowserve local office. They might provide me with more information.

 

-Leo