![]() ![]() The key to understand the difference between Double Block & Bleed (DBB) and Double Positive Isolation (DPI) can be found in API 6D. While this may seem like a small matter, but in reality it means that some users may think they’ve achieved positive isolation when they haven’t. ![]() Many people take the term “Double Block & Bleed” (DBB) to mean the same thing as “Double Positive Isolation” (DPI). Shut off and vent pressure measuring instruments.Isolate instrumentation such as pressure indicators and lever gauges.Liquid service near waterways or municipalities.Remove equipment from service for cleaning or repair.It’s typically used where bleeding the valve cavity is required, where piping needs isolation for maintenance, or for any of these other scenarios: One actuator instead of two is required.ĭouble Block and Bleed Valve Applicationsĭouble block and bleed valves are most commonly used in the oil and gas industry, but can also be helpful in many other industries.All the valve components are housed in a single unit, the space required for the installation is dramatically reduced thus freeing up room for other pieces of essential equipment.The pipelines where these valves are installed can also be pigged without any problems.The valves are full bore with an uninterrupted flow orifice they have got a negligible pressure drop across the unit.There are significantly fewer potential leak paths within the double block and bleed section of the pipeline.This design also has operational advantages, Using a single unit double block and bleed valve system versus 3 separate valves saves installation time, weight on the piping system, and space. This style can isolate piping on both sides of the valve to vent/bleed the valve cavity between the seats. Single Unit Double Block and Bleed Valve provides double block and bleed in a single valve. Now you can de-pressurize the line downstream and open it up to work on it.” Types of Block and Bleed Valve Systems Single Block and Bleed ![]() You close the ball valve and open the bleeder. ![]() Just upstream is a double block and bleed valve-a trunnion-mounted ball valve with self-relieving seals and a bleed valve to vent the cavity. You don’t want to shut down the entire facility, so you decide to block off and depressurize just the section you’re working on. In simple terms as explained by ValveMagazine.Com, “It’s time to do maintenance on a section of process. Bleed valves will either be vented directly to atmosphere locally or via a hose connection / piping to an appropriate closed disposal system. Once isolation has been achieved in one or more of the main process isolation valves, the cavity that is created between these isolation valves can be drained through the bleed valve. This is achieved by two isolation valves (may be ball, gate, globe, needle, etc.) placed back to back, with a third bleed valve (usually NPS 0.75 or NPS 1 size isolation valve) in the center cavity. Double Block and Bleed Valves operate on the principle that isolation can be achieved from both the upstream and downstream fluid flow / pressures. ![]()
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