Double Block and Bleed functionality explained - Focus on API 6D and OSHA specification

Learn all relevant information about the DBB functionality, the relevant standards like API 6D and OSHA or how to achieve the best level of isolation in our short but very informative explanatory video. You can find more valuable information on the topic of DBB functionality and the different isolation levels in our blog. In our blog, we regularly keep you up to date with technical articles on numerous key topics related to DBB valves and their applications. Our hint for you: Subscribe to our newsletter today so that you will never miss a new blog article on the topic of DBB valves and their applications:

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The term Double Block & Bleed is defined by different organizations, such as API, OSHA and BVAA but also associations like EEMUA and companies like Shell.

For the Oil & Gas Industry API 6D and OSHA are the most important specifications.

Let`s have a look on both specifications!

According to API 6D edition 2022, a Double Block and Bleed Valve System is defined as “A valve with two or more sealing elements that, in the closed position, provides a seal against pressure from both ends of the valve with a means of bleeding the cavity between the sealing elements. ”You should be aware, that such a DBB valve does not provide positive double isolation when only one side is under pressure. For such an application, API 6D defines a DIB valve “A valve with two or more sealing elements, each of which, in the closed position, provide a seal against pressure from a single source, with a means of bleeding the cavity between the sealing elements.”

In contrast, OSHA defines only one Double Block and Bleed Valve System 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”.

Important to know is, that the API's DBB Type A and Type B definition, or even the DIB Type B definition does not achieve the same level of isolation as OSHA's, respectively API DIB Type A.

API Type B defines a DBB or DIB valve as one single valve with two seats, while the OSHA standard and
API Type A can only be achieved with two separate valves with a method to bleed pressure in between.
Through this, the isolation level is increased enormously.

So to sum up, you can say that OSHA is equivalent to API DIB Type A.

In which applications are the DBB valves used?
Double block and bleed valves are most commonly used in the oil and gas industry but can also be helpful in many other industries. It’s typically used where bleeding the valve cavity is required, where piping needs positive, high level isolation for maintenance, or for any of following scenarios:
 Prevent product contamination
 Remove equipment from service for cleaning or repair
 Meter calibration
 Liquid service near waterways or municipalities
 Transmission and storage
 Chemical injection and sampling
 Isolate instrumentation such as pressure indicators and lever gauges
 Primary process steam
 Shut off and vent pressure measuring instruments

There you have it!

We recommend the use of DBB valves with 3 independently operating valves which are incorporated in a single valve body and both block valves are sealing in one direction. For high tightness and double safety. Because safety is the driving force.


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