DBB Valve Selection

[Valving]

There are many experienced members and I would like to receive their comments regarding the DBB valve selection which is not very clear anywhere.
In my work, I located that the types of DBB valves are as follows
1.DBB Ball Vales (consisting of 2 valves)
2.Twin DBB Plug Valves (consisting of - 2 stems 2 plugs)
3.DBB Plug Valves
4.Through Conduit Slab Gate Valve
5.Through Conduit Expanding Gate Valve
6.Trunnion mounted ball valves with bleeding
7.Any other?

I understand that for real critical and high pressure applications and sealing must be granted, 1 and 2 is the best way. Pricewise, probably 2nd will be cheaper.

I read that 3,4,5 may not be providing good tighness.

I would be glad if you could share your comments
1.When you prefer 1 and 2?
2.I believe 1st option has limited sizes.
3.When could 3-4-5 be preferred?
4.Could anyone compare the prices of 1-2-3-4-5?


rgds to all

 

[sheiko]

Just for information:

http://www.eng-tips.com/faqs.cfm?fid=1612

"We don't believe things because they are true, things are true because we believe them."

 

[Valving]

Thanks for comments, I did not readh that clarification but similar ones.
My concern is more for other valves. plug, gate etc.

 

[zdas04]

I'm not sure why you've included gate valves in your list. They tend to not even be bubble tight, let alone suited for a poaitive energy isolation scenario. Same with plug valves.

And as to your question 4--yes, many people can compare the prices.

David

 

[Valving]

David thanks for your input.
Few companies specify Gate Valves as DBB and couple of vendors mention that the valves apply under the API6D design and testing, and insist that they are a zero leakage valve. (API598, API6)

Any further comments will be appreciated.

 

[HitokiriAoshi]

I will treat this as just, Double BLOCK, and bleed out the leak.

A trunnion ball valve with single piston effect seats on the upstream and downstream side with a bleed hole/valve in the cavity would be your lowest cost bet depending on size.

for gate valve and plug valves, you would need 2 of them, with a blood valve in between the two for it to act as double BLOCK and bleed.

You need to see how critical is this double block and bleed, for example, if it's just water/waste water, and you are just DBBing for maintenance purpose down the 2 valves, lowest cost solution is best, and it may be single ball valve or double gate valves depending on size.

However, if you need absolute isolation, such as poisonous or reactive chemical, i would use bubble tight valves and do true double block and bleed, maybe even the extra mile by using 2 DBI valves in a DBB configuration.