Double Block and Bleed Plug Valve is a type of plug valve designed to provide two sealing barriers (double block) and a means to vent/bleed the cavity between the seals.
It ensures positive isolation of process fluid for safe maintenance, sampling, or instrument connection. This design reduces the need for multiple valve assemblies, saving space and weight.
 

Description

1.Structure of Double Block and Bleed Plug Valve

Body: Cast or forged steel (carbon steel, stainless steel, alloy steel).
Plug: Cylindrical or tapered plug with port openings, sometimes sleeved or lubricated.
Seating: Soft-seated (PTFE, PFA, Nylon) or metal-to-metal.
Seals: Two independent sealing surfaces provide the double block function.
Bleed Valve/Port: Located between the two seals, allowing safe venting, pressure monitoring, or draining.
Operation: Usually quarter-turn (lever, gear, pneumatic, or electric actuator).
 Typical Construction
One-piece body or split body.
Top-entry or side-entry.
Fire-safe and anti-blowout stem design.

2.Standards of Double Block and Bleed Plug Valve

DBB plug valves are generally manufactured in compliance with:
API 6D / ISO 14313 – Pipeline valves
API 599 – Metal plug valves
API 6FA / ISO 10497 – Fire testing
ASME B16.34 – Pressure-temperature ratings
NACE MR0175 / ISO 15156 – Material for sour service
ISO 5211 – Actuator mounting
ASME B16.5 / B16.47 – Flanged end connections

3. Features of Double Block and Bleed Plug Valve

Double isolation with bleed capability.
Compact design compared to two valves + bleed valve system.
Quarter-turn operation for quick opening/closing.
Fire-safe & anti-static design available.
Bidirectional sealing (seals in both flow directions).
Low fugitive emissions design possible.
Various end connections: Flanged, Butt-weld, Socket-weld, Threaded.

4. Applications of Double Block and Bleed Plug Valve

Oil & Gas pipelines (liquid and gas).
Metering skids.
Storage terminals.
Offshore platforms.
Chemical & petrochemical plants.
Where positive isolation and safe venting are critical (maintenance, sampling, testing).

5. Operation of Double Block and Bleed Plug Valve

Open position: Plug port aligns with pipeline → full flow.
Closed position: Plug rotated 90° → flow blocked.
Bleed: Cavity between two sealing surfaces can be vented/drained through the bleed valve.
Can be manually operated (lever/gear) or automated (actuator).

6. Maintenance Manual (General) of Double Block and Bleed Plug Valve

Routine Maintenance Steps
Inspection
Regularly check seals, plug lubrication (if lubricated type), and bleed valve.
Monitor for leakage through bleed port (indicates seat wear).
Lubrication (for lubricated plug type)
Inject sealant through lubrication fittings.
Ensures smooth operation and extended life.
Seal Replacement
Isolate and depressurize system.
Remove bonnet/cover.
Replace seats, O-rings, or plug sleeves.
Operation Check
Cycle valve fully open/closed to verify smooth rotation.
Confirm bleed port opens and closes correctly.
Storage & Preservation
Keep valves in dry condition.
Protect machined faces with rust preventive.
Store with plug partially open to avoid sticking.
 

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