Use our free double block and bleed valve selector to instantly find out whether your isolation duty needs a DBB valve, a DIB-1, a DIB-2, or whether a standard ball valve is sufficient. Answer five quick questions about your isolation requirement, media, pressure class and maintenance driver — the tool returns a clear recommendation with the ball valve type and the API 6D reasoning explained in plain English.
A double block and bleed (DBB) valve is a single valve with two seating surfaces that, in the closed position, seals against pressure from both ends and provides a means of bleeding the cavity between the seats. This lets you isolate and prove the seal — something a standard single-isolation valve cannot do. Typical applications include instrument and meter isolation, sampling, calibration ports and chemical injection points on pipelines of all sizes.
Supports all API 6D isolation categories: DBB, DIB-1 and DIB-2. Choose your duty parameters and get an instant recommendation with the comparison table and key decision factors. Need to size the valve first? Use our Valve Cv Calculator to find the required flow coefficient before specifying isolation type.
When do you need a double block & bleed valve?
You need a double block and bleed valve when a single shut-off isn’t enough — when you have to isolate a line and prove the seal before working on it. A standard ball valve seals once and gives you no way to confirm it has actually sealed; a DBB has two seating surfaces with a bleed port between them, so you can isolate from both ends and vent the cavity to verify isolation. Typical triggers are instrument and meter isolation, sampling, calibration, chemical injection points, and pipeline maintenance. If people work downstream or the media is hazardous, step up to a DIB, which adds an independent backup seal.
DBB vs DIB: what the standard actually says
“Double block and bleed valve” is one of the most misused terms in valve engineering, because the same words mean different things to API, OSHA and various operators. This selector uses the API 6D / ISO 14313 definitions, which describe a single valve with two seating surfaces — not the old two-valves-and-a-spool arrangement. Understanding which type is needed is especially important when selecting brass ball valves or stainless steel valves by type for high-integrity duties.
DBB (Double Block & Bleed) — a single valve with two seating surfaces that, closed, seals against pressure from both ends, with a means of bleeding the cavity between the seats. Note: it does not give positive double isolation when only one side is pressurised.
DIB (Double Isolation & Bleed) — a single valve with two seating surfaces, each of which independently seals against pressure from a single source. The second seat is a genuine backup barrier in the same direction.
The distinction that matters on site
The practical difference: on a DBB, if someone is working downstream and the upstream seal leaks, the second seat will not hold in that same direction. On a DIB it will. That’s why high-consequence isolation — vessel entry, pigging, hot work — calls for DIB rather than DBB. Trunnion-mounted ball valves by size are the standard platform for all DBB and DIB duties because their seat design supports cavity bleed and self-relief.
DIB-1 vs DIB-2
- DIB-1 — two independent bidirectional seals; double isolation in both directions. The highest isolation level.
- DIB-2 — two seals in one direction, a single seal in the other (typically a bidirectional seat paired with a unidirectional seat).
Not sure which Cv you need for your DBB or DIB valve? Use our Valve Cv Calculator to size the valve first, then return here to confirm the isolation category. For pressure drop across the selected valve, see our Valve Pressure Drop Calculator.
How to use this selector
- Choose your isolation level — single shut-off, seal verification or two independent barriers.
- Select the pressure direction — whether isolation must hold from one side or both.
- Specify the media — benign, hydrocarbon process fluid, or toxic/high-hazard.
- Enter the pressure class — ASME Class 150, 300–600, or 900 and above.
- Set the maintenance driver — routine shut-off, instrument isolation, or entry/maintenance downstream.
The result panel shows your recommended valve type (DBB, DIB-1, DIB-2 or standard ball valve) with the decision reasoning and a comparison table across all four types. Use the “Change last answer” button to explore alternatives. For full valve selection or a quotation, contact our team.
Frequently Asked Questions
What is a double block and bleed (DBB) valve?+
API 6D defines it as a single valve with two seating surfaces that, when closed, seals against pressure from both ends of the valve, with a means of venting or bleeding the cavity between the seats. Importantly, the standard notes a DBB does not provide positive double isolation when only one side is under pressure.
What is the difference between DBB and DIB?+
A DBB seals against pressure from both ends of the valve. A DIB adds an independent second seal against pressure from a single source — so if the first seal leaks while someone works downstream, the second still holds in that direction. Use DIB where you need two genuine independent barriers in the same direction.
What is the difference between DIB-1 and DIB-2?+
DIB-1 provides two independent bidirectional seals — double isolation in both directions. DIB-2 provides two seals in one direction and a single seal in the other, usually a bidirectional seat paired with a unidirectional seat. DIB-1 is the highest level of double isolation.
When do I need a DBB instead of a standard ball valve?+
When you need to positively isolate a section for maintenance, instrument calibration, sampling or entry and verify the seal by bleeding the cavity between seats — common on pipelines, metering skids and chemical injection. A standard ball valve gives single isolation with no way to prove the seal.
Does a DBB valve replace two separate valves?+
Yes — an API 6D DBB or DIB is a single valve with two seating surfaces, replacing the traditional two-valves-and-a-spool (OSHA-style) arrangement. It saves weight, space, leak paths and installation cost, which is why trunnion ball valves dominate pipeline isolation.
When do you need a double block and bleed valve?+
Whenever a single shut-off isn’t enough — when you must isolate a line and prove the seal by bleeding the cavity between two seats before working on it. Typical triggers: instrument and meter isolation, sampling, calibration, chemical injection, and maintenance needing verified isolation. If personnel work downstream or media is hazardous, step up to a DIB for an independent backup seal.
What is the difference between a DBB and a standard ball valve?+
A standard ball valve gives single isolation with one effective seal and no way to confirm it sealed. A DBB has two seating surfaces and a bleed port between them, so you can isolate from both ends and vent the cavity to verify the seal. The DBB replaces a standard valve wherever proven isolation, seal verification or a second barrier is needed.
Definitions per API 6D / ISO 14313 (Specification for Pipeline and Piping Valves). Guidance tool only — final isolation philosophy must follow your project specification and risk assessment.
