DIB ball valve provides a seal against pressure from a single source, with a means of venting/bleeding the cavity between the sealing surfaces.
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DIB ball valve definition in API 6D:
Single ball valve with two seating surfaces, with two sealing surfaces, each of which, in the closed position, provides a seal against pressure from a single source, with a means of venting/bleeding the cavity between the sealing surfaces. This feature can be provided in one direction or in both directions
Two types of DIB ball valves:
DIB-1 Ball Valve: Double Piston Seat x Double Piston Seat
For the DIB Double Piston x Double Piston (DIB-1)configuration, over pressurization of cavity is external with a safety valve.
Upstream and downstream sealing; pressure energized; two seats are bidirectional sealing seats.
Advantage: Each seat can isolate the fluid from upstream and downstream, if one seat is damaged, the other seat still work to ensure the sealing performance.
DIB-1 Ball Valve
DIB-2 Ball Valve
DIB-2 Ball Valve: DPE Seat x Self Relieving Seat
For the DIB Self relieving x double piston (DIB-2) configuration, cavity over pressurization is internally controlled within the line.
Upstream and downstream sealing; pressure energized; one seat is bidirectional seat and one seat is unidirectional sealing seat.
For DIB-2 Ball Valve, the fluid can be relieved from one seat to downstream side.
Advantage: Self-relieving seat, no need to assembly the safety valve for pressure relieving.
Both DIB-1 & DIB-2 are for trunnion mounted ball valve structure.
The double block and bleed valve is abbreviated to DBB valve. It is made up of two ordinary ball valves linked by a common inlet end. The double block and bleed ball valve is a product intended to substitute several connections between conventional valves; as the name suggests, it is a double block and bleed ball valve. The distinction between this DBB valve and the conventional one is that it can effectively overcome leakage that happens during system operation, and it can be quickly closed and can discharge easily. This DBB ball valve is a modern form of valve that is commonly used on the market today.
What is a Double block and bleed Valve?
Two agencies officially describe Double block and bleed valve in different terms.
Double-block-and-bleed valve (DBB) is defined by API 6D as a &#;single valve with two seating surfaces that, in the closed position, provides a seal against pressure from both ends of the valve with a means of venting/bleeding the cavity between the seating surfaces.&#; When just one side is under pressure, this valve does not have positive double isolation, according to the note.
And OSHA defines DBB valve as &#;the closure of a line, duct, or pipe by closing and locking or tagging two inline valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves&#;.
Double block and bleed valve classification.
DBB valves are classified by their body structure into two main types:
Modular or Split Body Type DBB Valve &#; The main feature of this design is that it has two balls in one valve to ensure greater safety. A drain needle valve is located between the two balls on the Double Block & Bleed valve. This allows the valve to be drained and the pressure to be reset to zero. Instrumentation and piping all benefit from the modular form, three-piece body construction. Instrumentation valves range in size from 1 inch to 3 inches; piping valves range in size from 1 inch to 24 inches. API 3.000 to API 10.000 in all pressure class scores from 150 to lbs.
Integral DBB Valves &#; These valves are used in the instrumentation industry and come in a variety of designs to meet a variety of needs, including flange to flange, flange to the thread, injection, and sampling, and ball and needle types. A drain needle valve is located between the two balls on the Integral Double Block & Bleed valve. This allows the valve to be drained and the pressure to be reset to zero.
Features and Benefits of DBB Valve.
Double Block and Bleed valves have been developed to substitute the process of bolting the individual valves together to provide dual insulation.
This new model provides excellent savings in weight, space, and installation time, particularly for insulation in the instrument or instrument cage. These weight savings will amount to up to 60% and tests have shown that a time savings of 70% on installation is also possible. The biggest benefits must be seen, however, in reducing the leakage pathways into the environment, thus reducing the possibility of possible dangers.
Dual isolation is an essential requirement when maintenance is performed downstream of the first isolation valve. Cavity venting is given by either a ball or a globe vent valve such that the compressed pressure between the two isolation valves is vented safely.
These valves have also grown to incorporate the role of chemical injection and sampling points. In-built control valves are also incorporated into these valves.
Application of Double Block and Bleed Valve.
DBB valves are used where critical sealing is necessary to make sure no leakage occurs. Both valves can operate in various applications and industries, such as the Natural Gas industry, petrochemical, transmission and storage, industrial processes for natural gas, main-line and multi-purpose valves in liquid pipelines, and transmission lines of refined materials.
The demand for meters calibration is another application where the DBB valve is used. Each valve closed to the meter device must be tightly sealed. Even a minor leak causes errors in meter calibration and the inaccurate meter factor remains until the next proven procedure and large sums are required. Choosing the right DBB or DIB valve tested for API will help ensure the calibration is accurate almost every time.
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Double-Block Valves and Double Block and Bleed Valve
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(Petroleum)
(OP)
5 Mar 03 23:18Does anyone know the application of double block and bleed valve, i understand this valve consists of double seats with a body bleed, is it correct? Aslo, i heard that in case the pressure rating 900 and above, the double block valve (Two valves seried with a bleed) shall be applied. Double Block and Bleed valve shall not be considered for this application.
For this, do they have any code or standard concerned this matter. Your help will be very appreciated.
Replies continue below
(Mechanical)
6 Mar 03 16:24Nottingham,
The application of double block and bleed valves has usually been client driven in my experience. I am not aware of any code or standard that requires the double block and bleed.
On my current project we are using two types of single body, double block and bleed valves. For ANSI class 600 and below we use a twin seal plug valve. For ANSI class and above we use an expanding slab gate valve.
(Chemical)
7 Mar 03 14:07A double block & bleed is not a type of valve, but a valve arrangement. It consists of 2 gate valves in series (this gives you your double block) and typically a 3/4" gate valve stubbed in between the two gate valves (this gives you your bleed).
This valve arrangement is meant to give you positive isolation. The 2 gate valves in series are closed and the pipe segment between them is depressured via the 3/4" bleed valve. A pressure gauge can be connected to the bleed valve or it can be connected to flare. If the first block valve passed you can tell so by the pressure gauge or its contents can be routed to flare.
Note: A bouble block and bleed is only consider positive isolation when the pipe segment between the 2 block valves can relieve continuously to a lower pressure than whats being contained by the block valves.
Hope this helps!
(Mechanical)
10 Mar 03 07:18Nottingham, whilst Double Block & Bleed is an arrangement it can be acheived using a valve arrangement of twoo isolation valves in series with a bleed isolation valve in between, or using a single bodies double block & bleed valve.
Certainly within certain provinces in Canada, depending on the province their is legislation permitting or not permitting certain DBB single bodied arrangements. As Andrew TX states its usually client driven, based on the companies isolation philosophy and HAZOP studys performed.
For example BP have a preference for Double Expanding Gate valves, then Solid Slab Gate Valves, and thirdly Double Piston effect Ball Valves onyl when space cannot permit the use of the other two. Expanding Gate produces a mechanical seal on both sealing surfaces, where as solid slab relies on seat springs and line pressure to seal.
For smaller instrument connections Integral DBB's (i.e. Oliver, Galperti, Kenmac type) are frequently used to save weight (offshore) and uses the second block valve within the unit as the first instrument isolation (check out EEMUA 182).
(Mechanical)
10 Mar 03 16:07double block and bleed is required by code in section I (boiler ) service if there are 2 or more boilers interconnected on a common steam line and the boilers have a manway in the steam drum. This is to avoid cooking the maintenance person that enters the steam drum on the idle boiler . A similar philosphy would be prudent for any pressure vessel that a person can enter , if the vessel is interconnected to another active system which has dangerous fluids.
(Mechanical)
10 Mar 03 21:43For safe working in a confined space such as a vessel, it may be necessary to have such a valve installation. The Statutory Authority responsible for Occupational Health and Safety in your area is a good start. Australian Standard AS titled "Safe working in a confined space" makes reference to double block and bleed arrangements and their use.
(Mechanical)
13 Mar 03 08:26A double block and bleed valve is used where positive isolation between two processes is required, but where the piping systems must occasionally be connected. It is almost always a gate valve with discs that can both be positively seated on each seating surface. A good example is a double disc parallel seat gate valve that uses a wedge arrangement (actuated by the downward push of the stem) to push both discs against their respective seats. The bleed is a drain drilled at the bottom of the run so as to detect leakage as well as prevent pressure build-up that might be great enough to push the fluid into the adjacent process.
A flexible wedge valve can be used as a db&b, but only if it has been specifically designed to do so. The force of the stem must not only cause the two discs to conform to the seat plane, but also with sufficient force to seal the seat against leakage and dP.
Double block and bleed arrangements, where there are two conventional isolation valves with a drain between, are required when a boiler is being worked on and is attached to a process steam line supplied by (an)other(s). A single valve cannot be used even if it is designed as a double block and bleed.
(Chemical)
13 Mar 03 12:49I would never want to enter a vessel isolated by a double block and bleed, there have been too many people killed when the double block and bleed didn't do its job because the bleeder was plugged and the double block and bleed was lost.
Sure, it's possible to write a procedure with a double block and bleed that should work. For my own comfort, I'd want that vessel either blinded or it's physical disconnected so I know nothing is going to get in there when someone is in there.
My experience is that most facilites now require blinding or physical disconnects, double block and bleeds as isolation for confined spaces are either not acceptable OR if they are allowed, are just about impossible to get buy-off to do.
(Mechanical)
13 Mar 03 14:32Actually, there apparently are some plants thata have 2 or more boilers in service, interconnected, that do not have the double block and bleed.
Prior to about , the ASME code sect I required" one stop valve plus one non-return valve". Apparently, some vendors interpreted a non-return valve as a simple check valve, while other more prudent opinions were that a non-return valve is a stop/check valve combo. In any case, several medium sized boilers were installed in the period - that do not have effective double block and bleed when in combined/interconnected service.
Since , Section I eliminated the wording "non-retun valve" and now states the need for 2 stop valves plus telltale bleed.
(Mechanical)
4 Apr 03 00:58Double Block and bleed Valves can be explained as below.
*. A valve which seals on both upstream and Downstream Seat.
*. both the setas work independently of each other. Thus two different mediums can be separated by the valve.
*. The Fluid trapped in the body cavity could be released through the Bleed connection/Valve.
(Specifier/Regulator)
10 Jun 03 17:25We use Double Block and Bleed plug valves with two plugs in one body. We can replace a single plug valve with one of these valves to create a double block and bleed without piping modifications because the face to face dimension is the same as a single plug of the same flange rating. They come in most flange ratings. The bleed port can be purchased with 1/2" or 3/4" threaded or flanged. Some manufactures provide valve stems on opposite sides and others with stems on the same side. These valves are called many names, but we prefer to call them Tandem Plug Valve so it will not be confused with a valve arrangement of to two block valves and a bleed valve. Here is a few Websites.
(Industrial)
11 Jun 03 15:08First, I have enjoyed reading all the answers.
I am involved in Instrumentation and Interlock systems. My experience with double block and bleed valves has been on the fuel gas line on boilers, furnaces, and incinerators. When the boiler shuts down or trips the two block valves close and the vent opens.
The first time I came accross this was back in . A package boiler had this setup. The valves were called Maxon valves. The boiler interlock panel supplied 120 volts to the valves which allowed the operator to latch the block valves open and the vent closed. When the unit shutdown, the 120 volts were removed from the valves allowing the blocks to close and the vent to open. Since them I have run into a number of different configurations.
Mark
(Industrial)
26 Jun 03 03:52For Double block and bleed (DB&B), please go to the homepage www.bch.dk , who is the only supplier in the world of this arrangement in one single body (as it has been patented). You will have DB&B with same face-to-face dimension as for one single valve, thus, saving space. Furthermore, this DB&B, also called "twin plug valve", is cheaper and lighter that the normal DB&B arrangement.
(Petroleum)
26 Jun 03 10:02I agree with most here, double block and bleed is a client driven requirement(in my experience). I first ran into it with custody transfer of crude oil, & recently for safety reason on high pressure steam lines. I too would not enter a confined space with just a double block and bleed valve., here in the oil fields of Calif. we require spec. & pad blinds before entry is permitted. Good Luck! ...Mark
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