Blowdown rings

[bevjones2009]

Hi everyone, could you please point me in the direction of blowdown ring settings, I have a few tables, for such valves as Crosby and Farris, only a few settings, please could someone help me find more settings.

Thank you in advance.

 

[JAlton]

Ring Adjustments affect PRV Performance.
Incorrect settings may induce such problems as:
1) Chatter damages Internals (Seat Deformation Galling in Guide Area) also restricts Capacity (No Full Lift)
2) Flutter no damage to Seats, but may induce Galling and also restricts Capacity (No Full Lift)
3) Long Blowdown affects System Operation, may Overheat PRV causing subsequent erratic performance
4) Excessive Simmer may affect Set Pressure (Higher) also may cause Seat Damage due to Steam Cuts and possibly affect reseating performance if longer than Blowdown
5) Hesitant Reclosure (Looks like Long Blowdown on a Gauge) may keep valve open long enough to allow seat damage or impact System Operating Parameters

With a two (2) ring valve the following guidelines are helpful:
Raising the upper ring will decrease blowdown
Raising the lower ring will decrease simmer
Lowering the upper ring will increase blowdown
Lowering the lower ring will increase simmer

With a one (1) ring valve the following guidelines are helpful:
Raising the ring will decrease simmer and increase blowdown
Lowering the ring will increase simmer and decrease blowdown

Farris charts are very reliable. Crosby charts are also reliable. Dresser ring charts are available from their web site at

http://www.Dresser.com.

Select "Consolidated". Select "Literature". Select "Literature" in drop down menu. At Document Warehouse go to business unit and select "Pressure Relief Valves". Scroll down to bottom of screen and select "Technical Service Manuals". Click on "Search Documents". Then download as many different manuals as you need. Most have ring setting charts.

I hope you find this is helpful.



JAC

 

[bevjones2009]

Thanks Jalton, Very helpful.

 

[JAlton]

All PRV Manufacturers have "Final Factory Settings" in their Maintenance Manuals. The One (1) Ring Design PRV Charts are typically sufficient for 7 to 10% Blowdown. However, some PRVs have "Fixed Blowdown" so there is no setting or adjustment. Other than the Crosby, ASME Sec. III, Nuclear Service, Water Ring Design, no PRV has adjustable blowdown on Liquid.

For two (2) ring designs which are typically installed on ASME Sec. I, Power Boiler Applications, the "Final Factory Settings" were for many years condsidered "Field Starting Positions". However, ASME removed the requirements for Blowdown in ASME Sec. I with the exception of a minimum 2 psi or 2% od set, whichever is greater. This was to prevent Chatter and ensure full rated capacity.

Blowdown is not an important issue from an ASME Code perspective any longer. I have been in the business over 30 years, and never thought it would come to this point. Currently, unless an owner/user specifically requests a certain blowdown limit, the PRV Blowdown Control Elements (Rings) will be set in accordance with the OEM Published Settings.

JAC

 

[bevjones2009]

Thank you mate, you have been very helpful.