According to API 6D “Specification for PipelineValves” standards, a double block-and-bleed valve is 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 venting/bleeding the cavity between the seating surfaces.”

Block Valve. Any type of valve that is used to close off flow, such as flow through a pipeline or out of a tank. Types of valves used in such service include gate valves, ball valves, and plug valves.

It’s typically used where bleeding the valve cavity is required, where piping needs isolation for maintenance, or for any of these other scenarios:

Prevent product contamination

Remove equipment from service for cleaning or repair

Meter calibration

Liquid service near waterways or municipalities

Transmission and storage

Chemical injection and sampling

Isolate instrumentation such as pressure indicators and lever gauges

Primary process steam