Interpretation Double bloc and bleed

[shabbirvora]

We interpret double block and bleed function as DBB valve or manifolds used in instrumentations systems (Swagelok / Parker Style)

But for Bigger size pipe line valves (around 12") the same terminology is used (Kuka/Kace catalogues)
Can somebody add more on the mechanism of this type sealing
Thanks

 

[zdas04]

Double block and bleed is a technique that is mentioned in the OSHA rules as a valid method to isolate energy away from hot work (some of the others are insert-blinds and mis-aligning piping). They don't define it, but it is taken by most companies to be two sealing surfaces (the "double block") separated by a section of evacuated pipe (the "bleed").

Some companies require that the double block be two independent valves separated by some distance (from inches to miles), others consider a trunion ball valve with a functioning body bleed to be adequate. Some companies have restrictions on what can be done downstream of DBB (one company that I work with does not allow hot work in a confined space to be done downstream of DBB).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[Ashereng]

Some comapanies now require a second element in addition to a valve for a "block" upstream of hot work where there is potential for explosive conditions.

It is common for valves to leak. If relying on a double block and bleed in hot work, a flange or equivalent may also be used downstream of the block valve.

 

[jte]

Actually, OHSA does define a double block and bleed. See thread408-94849. Of course, companies often go beyond OSHA minimums, and individual states may have tighter restrictions also. California is one which allows DBB's for entry but with restrictions.

jt

 

[abeltio]

for work with hazardous products we used the DBB with spectacle blinds.

the sequence is as follows:
block valve
double flanged spool piece with bleed
spectacle blind
double flanged spool piece with bleed
block valve

saludos.
a.

 

[shabbirvora]

Can somebody share the sizes they have used and also advise some technically sound equipment provider?