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Understanding the Differences between Double Block and Bleed (DBB) and Double Isolation Bleed (DIB) Valves

January 31, 2024

In the realm of piping system design, selection, and industrial safety, comprehending the distinctions between Double Block and Bleed (DBB) valves and Double Isolation Bleed (DIB) valves is crucial. This blog aims to elucidate the fundamental disparities between each valve type and shed light on their applications.

Double Block and Bleed Valve (DBB)

A DBB valve is engineered to enhance two inline isolation points, creating a barrier between the upward and downward sections of a piping system. This prevents cross-contamination or contamination between two fluid flows. Commonly used in petrochemical, oil, and gas applications, DBB valves consist of two interconnected but separate shutoff valves and an interconnecting bleed line.

In the first stage, an isolation valve ensures a perfect closure of the upstream fluid, preventing it from flowing downstream. The second stage uses another isolation valve to create an additional barrier, while a bleed line connects the two valves for releasing any moisture or pressure from the system. Selecting a DBB valve is critical, especially when handling hazardous and volatile media, as zero communication between upstream and downstream fluids is essential for safety.

Double Isolation and Bleed Valve (DIB)

The DIB valve is a specialized valve used in piping systems, combining pressure relief and isolation in two stages. It facilitates quick shutoff, particularly in the transportation of hazardous fluids. Widely employed in gas and oil plants, cold storage plants, industrial processes, and nuclear power plants, the interior stage serves as the main isolation point, fully isolating fluid and the system. The second stage consists of two separate venting points to safely release pressure on the downstream side, preventing safety issues.

DIB valves, typically made from anti-corrosive materials like stainless steel and carbon steel, boast a longer service life. Their internal volumes are designed to eliminate the need for large-scale drainage or containment vessels, making them suitable for limited installation spaces.

Differences between DBB and DIB Valves

Both DBB and DIB valves play vital roles in the gas and oil industry, controlling fluid flow in process systems and pipelines. Understanding the key differences is crucial for selecting the appropriate valve for a specific application:

DBB Valve

  • Operates with two closure components and a bleed valve in between, creating a double block and bleed arrangement for isolation.
  • Utilizes two sealed chambers for enhanced safety features.
  • Complex and large in size, occupying ample installation space.
  • Bleed valve releases pressure build-up for safe opening and closing.

DIB Valve

  • Uses a single seal for isolation, resulting in a simpler and more economical design than DBB.
  • Smaller in size, suitable for installations with limited space.
  • Operates with three closure elements and one bleeding valve.
  • Provides an extra level of isolation, suitable for areas where leakage could have severe consequences.

Figure: A schematic of the DBB valve on the left and DIB valve on the right.

Factors to Consider When Selecting Between DBB and DIB Valves

  1. Available Space: Consider the space constraints for installation.
  2. Required Level of Security: Assess the criticality of isolation and security in your application.
  3. Budget Constraints: Evaluate the economic feasibility of each valve type.
  4. Specific Benefits and Features: Understand the unique advantages offered by DBB and DIB valves.

In conclusion, a comprehensive understanding of these valves’ nuances empowers you to make informed decisions based on the specific requirements of your piping system.

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