What is DBB and DIB ball valve?
First we need to clarify two kinds of sealing: the SPE and DPE.
SPE single piston effect: it is also call unidirectional seat design. When upstream pressure is higher than cavity pressure, the seat will seal; while the cavity pressure is higher than upstream pressure, it
DPE, it is called “bi-directional seat”, no matter the cavity pressure is higher or not, the valve will seal.
DBB Ball Valve
If a ball valve’s two seat are made of SPE seat, it is call DBB ball valve, double block and bleed ball valve. The advantage is that when the cavity pressure is higher than downstream, the valve seat will relief the pressure to the downstream. The disadvantage is that when the upstream seat is broken, the fluid will leak to cavity and then leak to the downstream and cause leakage.
DIB-1 Ball Valve
It is ball valve with double DPE seat. Call double isolation and bleed ball valve. The advantage of this kind of ball valve is that if the upstream seat is broken, the fluid will flow to cavity and force the ball against the downstream seat and use as secondary seal. No leakage will happen. The disadvantage is if the cavity pressure is high than the upstream pressure, it can be relive cause dangerous conditions. So if DIB ball valve, a safety valve is need to be install to bleed the cavity pressure to protect the valve.
There are also one kind of DIB-2 ball valve, which combine the advantage of SPE and DPE seat. That means one side use uni-directional seat (SPE) and the other side use bi-directional seat (DPE). It combines the advantages of DBB and DIB-1 ball valves.
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