With the need for verifiable and maintainable shut off in safety critical applications, double block and bleed valves have commonly been used for primary and secondary tight shut off, in an attempt to provide and ensure system integrity. Historically, system integrity would be achieved through the use of two individual isolation valves, a spool piece and a bleed valve that had the disadvantage of extensive cost and weight and also increased the risk of emissions due to multiple flanged faces. Consequently, integral DB&B valves are now widely used.
These valves have a single or side entry body design with dual Ball with a bleed valve installed between the two main line valves. These valves are available bi-directional in metal seated and soft seated style, in bubble tight shut off. Sometimes called twin valves, are available up to ANSI 150 2500 class. These DB&B design valves replace existing traditional techniques employed by pipeline engineers to generate a double block and bleed configuration in the pipeline.