DB&B VALVES
DB&B VALVES
(OP)
Hi
I have a very very urgent question about application of double block & bleed valves,single block & bleed valves ; where and for what working classes these are necessary ?
My question is for a crude oil metering system and the maximum working class is 600# ; please inform me about some site addresses
thanks a lot
I have a very very urgent question about application of double block & bleed valves,single block & bleed valves ; where and for what working classes these are necessary ?
My question is for a crude oil metering system and the maximum working class is 600# ; please inform me about some site addresses
thanks a lot





RE: DB&B VALVES
They aren't necessary for any piping class in the sense 'over this rating, you must provide x, y and z'. Your question is a little broad so I'll go through a very general description.
That said, it's tyically driven out of operability and safety concerns. Single block valves are for stopping the flow. They also provide isolation if you need to work on downstream equipment. Think of the block valves around a control valve.
Single block with a bleed valve is to allow you to drain either the upstream or downstream side, depending which side (or both) the bleed is one. Also common on control valve manifolds for that reason.
Double block and bleed are used to provide additional safety and/or isolation. Essentially, you have two closed valves with an open bleed between them. If both valves are closed and the bleed is opening and functioning, you know you can't get flow into the section that has been isolated. Blinds are another way of providing positive isolation. On a metering stations, I've also seen double block and bleeds used to ensure no flow through a bypass where it would affect the accuracy of the meters.
RE: DB&B VALVES
To be more specific i have often seen that on parallel trains where one train may be taken out of service while the other are running (and here metres could be a good example) and where the pressure class is =>900# there you will ud DB&B. But the use will often depend on company standards.
Best regards
Morten
RE: DB&B VALVES
The use of DB&B is independent of pressure classes.
Their use is to ensure a better isolation.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
RE: DB&B VALVES
RE: DB&B VALVES
we are using DB&B for level bridles (LB) on the equipment on site which are mainly class 1500#. When they want to perform CFT on the (LB), they close both blocks while the equipment is in operation. The issue is reopening the first block valve adjacent to equipment is extremely hard due to high delta P across the valve. Can anyone advise what is the best practice to reopen this valve?
The valves we are using are Hi-lock DB&B.
RE: DB&B VALVES
They are also used between or in front of meters at a custody transfer point where it would be unacceptable to have one meter working while the other meter was leaking product across it too. Likewise, it is also common to find these at any point or pipeline branch where a loss of product would be dangerous or could mean lost revenues. This would typically be at custody transfer points from a gas/oil producer to the meters as they enter a pipeline owned by others, between refineries, between process units where revenues are accounted for separately, etc.
RE: DB&B VALVES
RE: DB&B VALVES
The connection is 2". Can we use gate valve?
RE: DB&B VALVES
RE: DB&B VALVES
I am just asking with using a globe, do we eliminate this problem? I know this problem exists with balls forever. As this valve upstream of Level Bridle is normally fully open or closed, I do not see any issue with using Gate valves.
Cheers
RE: DB&B VALVES
RE: DB&B VALVES
By the way, can I ask where you are working? Would you mind me asking for your email address? I am in Australia.
Rgds
RE: DB&B VALVES
Sure thing. Please see,
http://virtualpipeline.spaces.msn.com/
RE: DB&B VALVES
RE: DB&B VALVES
MARKFLOW
RE: DB&B VALVES
RE: DB&B VALVES
So far i have only seen arguments that DBB should be used for positive isolation of equipment. One example is HP systems e.g. for parallel trains.
Best regard
Morten
RE: DB&B VALVES
"Double block and bleed valves are used where positive isolation and assurance from flow leaking from upstream to downstream of a valve is required, nothing else. It has nothing to do with pressure class and little to do with safety."
DBB are very much a part of a safety program especially if you have a LT&T system in a facility.
RE: DB&B VALVES
Best regards
Morten
RE: DB&B VALVES
RE: DB&B VALVES
Best regards
Morten
RE: DB&B VALVES
RE: DB&B VALVES
Reduced bore means it is smaller. You need to check each valve manufacturer's definition of reduced bore, but it is usually the next size down.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?