Product Description
Double block and bleed (DBB) is the practice of shutting in a section of pipe on both sides of the valve rather than just one. It means you close the ball valves to block both the upstream and downstream sides of your working area, and then bleed any pressure that remains in the piping and valve
API 6D defines a double block and bleed valve as a 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 vending/bleeding the cavity between the seating surfaces