Question 1

What is a double block and bleed (DBB) valve and how does it work?

Accepted Answer

A Double Block and Bleed (DBB) valve is a single valve assembly that provides two independent sealing surfaces — upstream and downstream seats — that both independently seal against the process fluid from each direction, combined with a bleed (vent) port that drains the cavity between the two seats to atmospheric pressure. When the valve is closed, both seats are engaged. The bleed port is then opened to vent the inter-seat cavity. If both seats are holding, no fluid flows through the bleed port — confirming the integrity of both seals before downstream maintenance begins. The DBB function in a trunnion mounted ball valve operates through the spring-loaded downstream seat holding under both pressure directions. An expanding gate valve achieves DBB via a split gate and seat wedge mechanism that expands to seal under both upstream and downstream pressure. API 6D (ISO 14313) defines the specific leakage test requirements for DBB valves.

Question 2

When does Saudi Aramco specify double block and bleed valves?

Accepted Answer

Saudi Aramco specifies DBB valves for: (1) pipeline isolation before maintenance when the downstream section must be vented and verified clear of pressure before opening; (2) emergency shutdown valve (ESD) stations in classified hazardous areas where a single valve isolation is insufficient; (3) sampling connections and pig trap isolation where the upstream pressure must be verifiably blocked on both sides; (4) chemical injection and chemical dosing block valves; (5) crude oil meter runs and fiscal metering isolation where zero leakage verification is required. The SAEP-347 Annex 4 and associated Saudi Aramco piping class documentation indicate DBB as a specific valve class (not just any trunnion ball valve) — the valve tag will be designated 'DBB' or 'TBV-DBB' in the process control documentation.

Question 3

What valve types can provide double block and bleed (DBB) capability?

Accepted Answer

Three valve types can provide genuine DBB capability as defined in API 6D: (1) Trunnion mounted ball valves — the most common DBB valve type in Saudi Aramco pipeline and process applications; the spring-loaded upstream and downstream seats independently seal against the fixed ball, and the body cavity between them is connected to a bleed valve; (2) Expanding gate valves — a split gate and seat plate mechanism that expands to seal both upstream and downstream when the gate is closed, with a cavity bleed connection; (3) Double isolation and bleed (DIB) plug valves — less common in the Saudi Aramco hydrocarbon sector. A standard floating ball valve or conventional gate valve does NOT provide DBB function — it seals only in one direction. When a Saudi Aramco drawing or purchase order specifies 'DBB', the valve must be explicitly designed, tested, and certified for double block and bleed service per API 6D.

Question 4

What is the difference between DBB (Double Block and Bleed) and DIB (Double Isolation and Bleed)?

Accepted Answer

API 6D distinguishes between DBB and DIB based on the pressure direction the seats seal from: DBB (Double Block and Bleed) requires each of the two seats to seal from a different pressure direction — the upstream seat seals from upstream pressure, the downstream seat seals from downstream pressure. Both seats must independently hold before the bleed port is considered verified. DIB (Double Isolation and Bleed) is a higher standard — both seats must independently seal from the same pressure direction (upstream), meaning the downstream seat also blocks upstream pressure without relying on downstream back-pressure. DIB is the more demanding specification and is required where a positive double isolation must be demonstrated under one pressure direction only — common in fiscal metering and certain hazardous area isolation applications. For Saudi Aramco applications, the piping class or valve data sheet will specify whether DBB or DIB capability is required.

الميزة	DBB	DIB
ختم المقعد	كل منهما من اتجاهين متعاكسين	كلاهما من المنبع فقط
API 6D	القسم 6.3	القسم 6.4
الاستخدام الشائع	إغلاق خط الأنابيب، ESD	القياس المالي، أخذ العينات
الصرامة	قياسي	أعلى

صمامات الإغلاق المزدوج والتصريف في المملكة العربية السعودية — API 6D، عزل خطوط الأنابيب والعمليات

الإغلاق المزدوج والتصريف — الوظيفة ومتطلبات أرامكو السعودية

أي أنواع الصمامات توفر وظيفة الإغلاق المزدوج والتصريف؟

الأسئلة الأكثر شيوعاً — صمامات الإغلاق المزدوج والتصريف

اطلب عرض سعر لصمامات DBB — API 6D، مخزون في جدة