Views: 0 Author: J-VALVES Publish Time: 2026-07-10 Origin: Site
In oil & gas transmission, petrochemical, cryogenic LNG and offshore facilities, trunnion ball valves with DBB, DIB-1 and DIB-2 double isolation & bleed functions are mandatory safety equipment for pipeline maintenance. The core difference lies in SPE single piston effect and DPE double piston effect seat design, which determines leakage protection, cavity relief and application range. Combined with real photos of DBB ball valves, DIB sectional drawings and cavity bleed test footage, this article explains sealing structures fully under API 6D standard.
Equipped with two SPE single piston seats, one-piece body with central bleed port. It provides bidirectional shut-off for upstream and downstream media. Operators can vent trapped fluid and test seat tightness without removing the valve from pipeline.Limitation: Two SPE seats only seal pressure from pipeline side. If upstream seat leaks, cavity pressure cannot form secondary seal on downstream side. It has built-in self-relief function without external relief valve, widely used for general industrial piping.
Each seat can independently isolate single-side pressure with redundant sealing, divided into DIB-1 and DIB-2, higher safety level than standard DBB for toxic, flammable and high-pressure medium.
DIB-1 adopts two DPE bidirectional seats on both ends. If upstream seat fails, accumulated cavity pressure will press downstream DPE seat tightly against ball to build a second isolation barrier, completely prevent medium penetration.
Disadvantage: No internal pressure relief channel, external safety relief valve must be installed to avoid cavity overpressure caused by thermal expansion. No flow direction restriction for installation.
DIB-2 combines upstream SPE single piston seat and downstream DPE double piston seat, integrating self-relief and redundant isolation performance, top choice for LNG and ultra-high pressure crude oil pipelines.
Working principle: Upstream SPE seat releases overpressure back to upstream pipeline automatically, extra relief valve is unnecessary; downstream DPE seat maintains reliable single-side isolation. Flow direction mark on flange, reverse installation forbidden.
1. Modular seat interchange: Switch DBB / DIB-1 / DIB-2 sealing structure on same valve body without new mould;
2. Ultra-precise ground sealing pair: Bubble tight shutoff Class VI soft seat, metal hard seat withstand -196℃ ~ +550℃;
3. Uniform spring preload: Circumferential high-temperature springs keep tight contact under low differential pressure;
4. Integrated bleed port: Reduce extra pipe fittings and potential leakage points;
5. Full international certification: API 6D, API 607 fire safe, anti-static, anti-blowout stem test passed for all trunnion DBB ball valves.
City gas, general chemical circulation, low-pressure water pipeline:J-VALVES DBB trunnion ball valve
High-pressure natural gas trunk line, transmission station: DIB-1 double isolation ball valve
LNG terminal, cryogenic tank outlet, offshore platform, hydrogen refueling station:DIB-2 hybrid seat ball valve
