Double Block-and-Bleed and Double Isolation-and-Bleed

DBB definitions

There are two entities in the United States that define DBB&#;API and OSHA. According to API, a DBB valve is 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." API also notes in this definition that this valve does not provide positive double isolation when only one side is under pressure.

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In contrast, OSHA describes DBB 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."

API's DBB definition does not achieve the same level of isolation as OSHA's. API allows DBB valves to be one single valve with two unidirectional seats, while the OSHA standard can only be achieved with two separate valves with a method to bleed pressure in between. There are some valves that utilize a twin-valve design. By combining two valves into one body, a twin-valve design reduces weight and potential leaks paths while meeting the OSHA requirements for double block and bleed.

Valve associations usually choose to follow either API's or OSHA's definition, but some have created their own handbook with their own definitions for industry terms. For example, the British Valve and Actuator Association (BVAA) defines DBB as "a manifold that combines one or more isolation valves, usually ball valves, and one or more bleed/vent, usually a needle-style global valve, into one assembly for interface with other components (e.g., pressure measurement transmitters, pressure gauges, and switches)."

Block and bleed valves are hydraulic manifold systems that provide a single component interface by combining a number of valves, particularly ball and needle valves. They are commonly used in the oil and gas industry and are beneficial in ensuring the supply of liquid upstream does not affect the system components downstream.

Knowing the types and advantages of block and bleed valves can be important when undertaking an industrial or commercial project.

In this post, we explore how block and bleed valves work, its different types, and advantages they offer.

How do Block and bleed Valves Work?

The block and bleed valve can be operated to restrict liquid from flowing into a particular component and later letting it flow out of the manifold.

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Double block and bleed valves, for instance, are single valves that have two seating surfaces. If the valve is closed, it offers an effective seal from both surfaces that allow the liquid to vent out. This type of isolation occurs when only one of the sides faces pressure.

Types of Block and bleed Valves

Different types of block and bleed valves offer different features. Block and bleed valves are also known as isolation valves or isolation manifolds. A manifold that features a number of valves is useful for using it in gas trains, as well as in various industrial contexts.

Other types of block and bleed valves include the double block and bleed valves, three piece non standard length double block and bleed valves, block and bleed needle valves, single unit double block and bleed valves, and cartridge type length double block and bleed valves.

The standard double block and bleed valves, for instance, are used for chemical injections under high pressure environments or for handling toxic fluid processes. Needle valves, on the other hand, are used in pneumatic and hydraulic systems.

Benefits of Block and Bleed Valves

Block and bleed valves are beneficial for preventing leakages or mixing of fluids with critical components. This makes it ideal for use in petrochemical environments where there is a need to handle and manage toxic waste and other dangerous chemicals.

The interlocking provided in the valve allows easy venting of the liquids and provides considerable safety in high-risk environments.

Furthermore, block and bleed valves are important for bringing operation and production costs to a minimum. The efficiency of the valves prevents the need for multivalve systems and ensures high project operational efficiency in a range of industries from LNG and petrochemical to natural gas processing.

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