PRV ASME I Valves 1

[gguliye]

Dear All,
May be my question is so basic, however, i am doing my hair off, because i couldnt come up to the result why

in ASME section I valves, we have 2 rings. Nozzle ring and guide ring. Why lowering guide ring decreases blowdown of the valve?
In my opinion it has to increase the blowdown. Could someone help me with this question?
Regards,

 

[gerhardl]

This would be better to comment if you posted a drawing exactly showing the mentioned parts, so we can be sure which is which.

I could have misunderstood your question, but I beiieve you mean 'lower the set pressure = actual blowdown pressure*, in which case the explanation could be as simple as that you slacken the spring pressure (elongates the spring), and it will thus require less force to open.

 

[gguliye]

Sir,
Here is the picture

 

[gerhardl]

OK, thanks! I think I was right, but depending of definition and understanding of 'lowering' = moving in which direction? If not satisfactory try to post in PSV forum!

 

[gguliye]

Dear Gerhardl,
Guide ring has nothing to do with the spring. There is another bolt for the compressing or decompressing the spring.
Guide ring has something to do with the changing the flow angle of deflection.
Is there anyone else who can write an answer for this?
Regards,

 

[Rputvin]

A lower guide ring has more force imparted on it and increases blowdown. Raising the guide ring lowers blowdown.

Page 44 of this document explains it well, using the same diagram you posted.

https://www.emerson.com/documents/a...-valve-engineering-handbook-en-us-3923290.pdf

 

[gguliye]

Rputvin,
Thanks, I didnt notice it before