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Double Block and Bleed Valve (FAQ)
A block and bleed manifold is a hydraulic manifold is a component which
regulates fluid flow between pumps and actuators and other components in a
hydraulic system. that combines one or more block/isolate valves, usually
ball valves, and one or more bleed/vent valves, usually ball or needle
valves, into one component, for interface with other components (pressure
measurement transmitters, gauges, switches, etc.) of a hydraulic (fluid)
system.
The purpose of the block and bleed manifold is to isolate or block the flow
of fluid in the system, so the fluid from upstream of the manifold does not
reach other components of the system that are downstream, then bleed off or
vent the remaining fluid from the system on the downstream side of the
manifold. For example, a block and bleed manifold would be used to stop the
flow of fluids to some component, then vent the fluid from that component's side of the manifold, in order to effect some kind of work
(maintenance/repair/replacement) on that component.
A block and bleed manifold with one block valve and one bleed valve is also
known as an isolation valve or block and bleed valve; a block and bleed
manifold with multiple valves is also known as an isolation manifold.
Double Block and Bleed are also used in combustionable gas trains in many industrial applications.
Double Block and Bleed Valves replace existing traditional techniques
employed by pipeline engineers to generate a double block and bleed
configuration in the pipeline.
Cartridge Type Standard Length Double Block and Bleed Valves have a patented
design which incorporates two ball valves and a bleed valve into one compact
cartridge type unit with ANSI B16.5 tapped flanged connections. The major
benefit of this design configuration is that the valve has the same
face-to-face dimension as a single block ball valve (as specified in API 6D
and ANSI B16.10), which means the valve can easily be installed into an
existing pipeline without the need for any pipeline re-working.
Three Piece Non Standard Length Double Block and Bleed Valves (DBB Valves)
feature the traditional style of flange-by-flange type valve and is
available with ANSI B16.5 flanges, hub connections and welded ends to suit
the pipeline system it is to be installed in. It features all the benefits
of the single unit DBB valve, with the added benefit of a bespoke
face-to-face dimension if required.
The single unit Double Block and Bleed Valve (DBB) design also has operational advantages, there are
significantly fewer potential leak paths within the double block and bleed
section of the pipeline. Because the valves are full bore with an
uninterrupted flow orifice they have got a negligible pressure drop across
the unit. The pipelines where these valves are installed can also be pigged
without any problems.
There are several advantages in using a Double Block and Bleed Valve.
Significantly, because all the valve components are housed in a single unit,
the space required for the installation is dramatically reduced thus freeing
up room for other pieces of essential equipment.
Considering the operations and procedures executed before an operator can
intervene, the Double Block and Bleed manifold offers further advantages
over the traditional hook up. Due to the volume of the cavity between the
two balls being so small, the operator is afforded the opportunity to
evacuate this space efficiently thereby quickly establishing a safe working
environment.