Sizing a PCV in steam service

[SrChemE]

Would somebody have the sizing program for a FIsher regulator?
I am in a catch 22 situation: don't know the flow rate passing through an old PCV and don't know the CV on the valve. There is the need to replace a relief valve downstream and the only way to size the RV is based on the failure of the control valve upstream.
How would you go about doing this? The PCV installed is so antient, it does not have any tags for specs.
It is a 3" Fisher regulator. I only found a tag on the 3" actuator, but it was barely readable.
Any thoughts?

 

[LittleInch]

Replace the regulator.

The time, effort and cost involved in doing anything else will pale into insignificance.

Your only other option is to find the data sheets, PFD etc for the design. Could you install a temporary flow meter or US clamp-on meter to measure flow and us/d/s pressure. What does this valve control on??

If you ask fisher they might have a max CV for the particular model, but it could be very high compared to what you actually have.

All in all - If it's that old it might be needing replacement any way....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[SrChemE]

LittleInch,
You are correct, we need to replace the valve, as old as it is. I contacted the vendor who was not able to locate any info on the valve. He gave me a CV based on the largest capacity of a 3" Fisher valve.
Unfortunally this valve supplies steam to several areas in the plant. If I get this wrong... this could cause shutdown and donwtime.
I really like the idea of the temporary flow meter to measure the actual flow, but there might not be enough space. The PCV valve is on a bypass and the only available piping is on a vertical line. It is worth checking though. I can get this arranged for the next shutdown if okay.
Thank you!