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DBB and DIB - is there (still) confusion?
Datetime: 2017-05-12    Visit: 144

Article 4.7 defines a double-block-and-bleed valve as “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” with an additional note that “this valve does not provide positive double isolation when only one side is under pressure”

Article 4.8 defines a double-isolation-and-bleed valve as a “single valve with two seating surfaces, each of which, in the closed position, provides a seal against pressure from a single source, with a means of venting/bleeding the cavity between the seating surfaces” with an additional note that “this feature can be provided in one direction or in both directions”.

To summarise:

a DBB is a valve that seals from either direction with a bleed between the two, if the first seal leaks, the second will not seal in same direction.
a DIB is a valve that seals from one direction with two separate seals and a bleed between the two. Here we have two seals from the same direction.
A DBB valve implies double security, but the difference is that it actually gives security in two different directions, each with a separate seal. The important distinction is when a DBB valve is in use and the first seal leaks the second seal will not seal in that same direction. Good, I’m making progress.

At this point the topic can be discussed further, depending on the type of valve used and it’s intended application.

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