DBB vs DIB Ball Valve
DBB and DIB terminology describes isolation behavior, not simply the number of valve seats. The seat direction and pressure response need to be understood before the required arrangement is specified.
Single-piston-effect and double-piston-effect seats influence how pressure is isolated across each seat and how the body cavity responds to pressure buildup.
The valve datasheet should state the required DBB or DIB philosophy, seat arrangement, cavity-relief requirement, upstream/downstream pressure cases, bleed connection and test acceptance.