The double block and bleed valve is also called DBB valve, generally say, it is make up by two ball valve and one neddle valve or two ball valve and a globe valve.

Why some conditions use the Double Block and Bleed valve?

Double Block and Bleed valves have evolved to replace and add the process of bolting together individual valves to make the valves in one body.it saved a lot of space and meterial, it is the development tendency of the valve in the future.

These new assembly of the double block&bleed valve provides great savings in weight, space and installation times especially in cage isolation. These savings can be as much as 70% in weight and shown that it can saving 70% installation time on the projects. However the greatest savings , therefore reducing the risk of the potential hazards this entails such as leak or insecure.

Dual ball is a necessary requirement when maintenance is taking place down stream of the first isolation valve.

These double bllock and bleed valves have also evolved to encompass the function of chemical analysis and mechanical character.  Cavity venting is provided by either two balls or globe OS&Y vent relief valve so that the pressure between the two isolation valves can be safely vented.