Due to the Special Operation of the pigging valve, so with the ball valve or is essentially different, API 6d ball valve DBB, DIB-1, DIB-2 and other structural functions. The pigging valve has only DBB structure function, DBB has double cut-off and relief function (two seals can keep sealed at the same time) . The DBB seat is a single piston seal. Dib double isolation and pressure relief (valves with two seating faces resist source pressure in the closed position through each of the cavities between the relief faces) .
When the pigging valve needs pigging operation, the DBB function pigging valve cuts off the pressure from both ends of the valve, the pressure of the relief valve cavity quickly opens the quick opening door to load the pigging device, and the quick opening of the quick closing door opens the pigging valve to enable the pigging device to enter the pipeline operation.
If is the DIB structure pigging valve must be installed safety valve, when the cavity pressure is too high, safety valve off relief, pollution of the environment. When a pigging operation is required to remove the pigging valve cavity pressure Dib structure into DBB structure so the pigging valve is DBB structure.