Double Block And Bleed Valve

What is a Double Block and Bleed Valve?

In essence, a DBB combines two isolation valves into a single unit, with a third valve placed between them to relieve pressure. This configuration ensures a secure blockage on either side of the system while allowing any trapped fluid to be safely discharged via the bleed valve. Double block & bleed instrument valve is typically used in applications where the system needs to be depressurized for maintenance or inspection without completely shutting down the entire process.

Double Block and Bleed Valves are an efficient way to enhance operational safety while optimizing system space by reducing the number of individual valves.

How a Double Block and Bleed Valve Works

A Double Block and Bleed (DBB) valve is designed to provide positive isolation in high-pressure and critical service applications. Its working principle is based on two independent sealing barriers with a bleed mechanism in between, ensuring maximum safety and leak prevention.

In a DBB valve, two block valves are positioned in series within a single valve body or valve assembly. These block valves are located on the upstream and downstream sides of the process flow. When both block valves are closed, they create two separate sealing points, effectively isolating the pipeline section from the process media.

Between these two block valves, a bleed valve or bleed port is installed. Once the main block valves are closed, the bleed valve is opened to release any trapped pressure or residual fluid from the cavity between the two sealing points. This step confirms that both block valves are sealing properly and that no leakage is occurring.

If fluid or pressure is detected at the bleed port, it indicates a leak in one of the block seals, allowing operators to identify issues immediately without exposing personnel or equipment to risk. This verification feature is a key safety advantage of DBB valves compared to conventional isolation valves.

In advanced DBB valve designs, such as single-body or monoflange configurations, all three functions—double isolation and bleeding—are integrated into a compact unit. This reduces potential leak paths, minimizes installation space, and improves system reliability. Metal-to-metal sealing, precision machining, and compliance with international standards further enhance performance in high-pressure and high-temperature applications.

Overall, a Double Block and Bleed valve works by isolating the process flow at two points and safely venting the cavity between them, making it an essential solution for applications where safety, maintenance efficiency, and regulatory compliance are critical.

Features

The Valves come with a range of advanced features that make them highly effective in critical applications:

• Isolation and Bleed Mechanism: Ensures two independent barriers for safety with a venting mechanism between them.
• Compact Design: Combines multiple valves into a single unit, saving space and reducing weight, while also minimizing the number of potential leak points.
• Pressure Rating and Size Range: Available in pressure ratings from #150 to #2500, Double Block and Bleed valves accommodate different system requirements, with sizes ranging from 8NB to 100NB.
• Body Materials: Manufactured from a wide variety of materials, including stainless steel, carbon steel, and specialty alloys, these Valves are built to withstand various environments. Temperature Range: Suitable for applications with temperatures ranging from -7°C to 280°C.
• Compliance with Industry Standards: These valves adhere to international standards like ASME B16.34 and API 598, ensuring optimal performance in demanding conditions.
• Leak Prevention and Safety:Double Block and Bleed Valve are fire-safe and meet sour service requirements under NACE MR0175 and ISO 15156 standards, making them reliable in harsh environments such as offshore platforms and chemical plants.