DBB double block and bleed, mainly used in valve
that has mentioned above. If it is BDD the root of the instrument,
which means root valve including 2 globe valve and 1 discharge
valve. It can be fission, composed by 3 valve. It can also be
integral, external have three operating handles. Besides, there
is another one used on pipeline named shutoff valve (such as ball
valve), requires when cavity bleed, both seat of upstream and
downstream should be closed.
The ball valve with DBB function is designed according to API
6D, used for long-distance pipelines on gas & liquid. DBB
namely double block and bleed, when the body cavity pressure fluctuation
seat will tightly hold ball, then both inlet and outlet seal.
Whether gas or liquid medium, safety valve must be set in body
to ensure pressure relief and discharge to atmospheric enviorment.
So whether it is necessary to use the ball valve with DBB function
should look the medium in the body cavity whether can be discharged
to atmosphere and do no harm when overpressure.
Meanwhile, another one is upstream seat sealing, which discharge
the pressure to downstream pipeline when overpressure without
safety valve.
All rights reserved by FBIC Inc., do remember to show the source
(www.fsbic.com) of the news when copying.
