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 Double block and bleed 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. Double block and bleed 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 2008 note.

Double block and bleed 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

Double block and bleed valve is classified by their body structure into two main types:

Modular or Split Body Type Double block and bleed 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 2500 lbs.
 

Integral Double block and bleed valve – 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 valve has 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.

Double block and bleed valve 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

Double block and bleed valve is 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.

Difference between DBB and DIB

API describes Double Isolation & Block Valve, DIB as a “single valve with two seating 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 seating surfaces.” This feature can be provided in one or both directions.

The main difference is that the double block and bleed valve protects against pressure from either side of the valve while the double isolation and bleed valve offers additional seal against pressure from just one side. It is necessary to use the DIB valve instead of the DBB valve in applications requiring an external pressure barrier to be sealed separately from the main pressure barrier. This is critical to meet such operational safety standards or depending on the type of the operation, such as low leakage tolerance of fluid cleanliness.

There are normally two unidirectional self-relieving seats with a DBB valve. These seats do not depend on an external pressure relief system. On the other hand, the DIB valve uses one or two bi-directional seats. The valve allows dual isolation from the pressure at both ends of the valve, but cannot ease the pressure of the body cavity past the seats. DIB valves need an external relief mechanism to ease the build-up of pressure.

Both valves could protect in both the upstream and downstream directions, even in high-pressure or high-temperature conditions. Isolation is critical in situations where leakage through the valve can have significant implications. Once the fluid is sealed, the bleed system may drain the area between the two valves or two seating surfaces. This is critical for maintenance and integrity checks in cases where leakage can be tracked.

How to select the right Double Block and Bleed Valve for your need

The main factors responsible for selecting the right Double block and bleed valve for your application are:

• The nature of the application will determine the kind of Double block and bleed valveyou require. For example, if you need to protect the system’s integrity when repairing a certain section of the pipeline, the double block and bleed valve can be used to do the job. The onstream can be blocked by two gate valves. A ball valve can vent the fluid from the blocked section of the pipeline until it is repaired.
• The kind of Double block and bleed valveyou select varies depending on the type of media you’re going to control. Viscous liquids and dense gases need a full-bore ball, globe, or gate valve as a block valve. The needle valve is often used as a bleed valve. Corrosive media can involve stainless steel Double block and bleed valve that have been secured to block the media without causing any harm.
• The temperature and pressure conditions of your operation would decide the type of Double block and bleed valve you need. High-pressure, high-temperature operations would include the use of anti-static ball valves as block valves. These ball valves are not affected by pressure fluctuations or vibration such that they are safe to use in sensitive operations. A single DBB gate valve with adjustable wedges and a body bleed valve can be used in low-pressure operations.