Flange Block-Bleed DBB

Quick Specs 2" - 20" (DN50 - DN500) Class 150 - 600 API 6D, API 607, ASME B16.34, ISO 15848 A216 WCB, A351 CF8M, A182 F51 PTFE, Nylon, PEEK, metal-to-metal (Stellite 6) Flanged end connections (RF/RTJ), bolted bonnet, double block & bleed in single body, manual or actuated operation

Flanged Connections——Where the Pipeline Specification Calls for Bolted End Connections

The flanged DBB valve serves the same isolation function as the trunnion DBB——two independent blocking seats with a verified bleed cavity between them——but with flanged end connections to the pipeline instead of butt-weld. Flanged connections (raised face or ring-type joint per ASME B16.5) are the standard pipeline connection method for Class 150 through Class 600 in many facility specifications——particularly on process piping systems where maintenance accessibility requires bolted connections that can be disassembled without cutting and re-welding the pipe. A butt-weld DBB valve (like the FLOWKS all-welded DBB series) permanently joins the valve to the pipeline——removal requires cutting the weld and re-welding a replacement. A flanged DBB valve unbolted from the pipeline flanges——four bolts per flange (on smaller sizes) or dozens on larger sizes, but the principle is the same: unbolt, remove, replace, re-bolt. No welding. No hot work permit. No radiographic inspection of replacement welds.

That bolted-connection accessibility is the primary reason facilities specify flanged DBB valves on Class 150-600 piping——the maintenance logistics of bolted connections are simpler, faster, and cheaper than welded connections on the pressure classes where flanged joints are structurally adequate. Above Class 600, butt-weld connections become the standard specification because flanged joints at Class 900 and above require heavier bolting, larger gasket surfaces, and higher bolt tensioning loads that push the flanged-connection maintenance complexity beyond practical limits for many installations. The FLOWKS flanged DBB covers Class 150 through Class 600——the pressure range where flanged connections serve the majority of process piping installations and where the bolted-connection maintenance advantage is most valuable.

Bolted Bonnet——Maintenance Access Without Removing the Valve from the Pipeline

The bonnet (the valve body section that contains the stem, packing, and the upper trunnion bearing) attaches to the body through a bolted bonnet-to-body connection——bolted, not welded. That bolted bonnet design provides maintenance access to the stem packing, the upper trunnion bearing, and the ball-and-seat assembly without removing the entire valve from the pipeline flanges. The maintenance procedure: unbolt the bonnet, lift the bonnet assembly (stem, ball upper pin, packing) out of the body, access the seat rings and ball for inspection or replacement, re-install the bonnet with new gasket, re-bolt, re-torque. The pipeline flanges stay bolted——the valve body stays connected to the pipeline throughout the maintenance operation. That in-line maintenance capability is the same principle that FLOWKS top-entry ball valves use for buried and welded pipeline service——the difference is that the flanged DBB's bolted bonnet serves flanged-connection installations where the pipeline flanges themselves are the primary disassembly point, and the bonnet bolts are the secondary access point for internal trim maintenance.

The bonnet-to-body gasket is a critical sealing element——it's the pressure boundary between the body cavity (exposed to pipeline pressure) and the bonnet cavity (exposed to packing and stem). The gasket specification matches the process media and temperature conditions: spiral-wound gaskets (stainless winding with graphite or PTFE filler) for general process service, metal-ring gaskets for high-temperature and fire-safe applications where spiral-wound gaskets would degrade under sustained thermal loading. The gasket gets replaced every time the bonnet gets unbolted——gaskets are one-time sealing elements, not reusable. That replacement requirement is standard maintenance practice across bolted-bonnet valve designs——you don't re-use a gasket on a pressure boundary, you install a new one every time the joint gets re-assembled.

Double Block and Bleed——Same Functional Architecture, Flanged Installation Package

The DBB isolation architecture inside the flanged body is identical to the trunnion DBB: two independent spring-loaded seats pressing against the trunnion-mounted ball from opposite sides, with a bleed cavity between them that vents through a designated port on the body. The upstream seat blocks process pressure from the active pipeline section. The downstream seat blocks pressure toward the isolated section. The bleed cavity verifies both seats simultaneously——zero pressure at the bleed confirms both blocking boundaries are holding. The functional behavior is the same regardless of the connection type (flanged or butt-weld): the seats seal, the bleed verifies, the isolation is double and independent.

The difference between the flanged DBB and the butt-weld DBB is entirely in the installation interface——flanged ends for bolted pipeline connection with maintenance accessibility, versus butt-weld ends for permanent pipeline integration with maximum structural integrity and minimum external leak paths. Both configurations deliver the same DBB isolation performance. The choice between them is driven by the facility's piping specification (does the line use flanged or welded connections at this size and pressure class?), maintenance philosophy (is in-line removal a requirement or is permanent installation preferred?), and the specific application's structural and regulatory requirements.

Flanged DBB: bolted end connections (RF/RTJ flanges)——removable from the pipeline by unbolting without cutting pipe. Butt-weld DBB: welded end connections——permanently joined to the pipeline, removal requires cutting the weld. Same DBB isolation function inside the body. Flanged for maintenance accessibility on Class 150-600 piping. Butt-weld for permanent installation and minimum external leak paths on Class 900+ piping or buried service.

Above Class 600, flanged connections require heavier bolting, larger gasket surfaces, and higher bolt tensioning loads that make flanged maintenance less practical than butt-weld. Butt-weld connections are the standard specification for Class 900-1500 piping——the structural integrity and leak-path elimination of welded joints outweighs the maintenance accessibility advantage of flanged connections at those pressure ratings. FLOWKS offers butt-weld and all-welded DBB configurations for Class 900-1500 applications.

In-line maintenance access to the stem packing, trunnion bearings, and seat/ball assembly without removing the valve from the pipeline flanges. Unbolt the bonnet, lift it out, service the internals, re-bolt with a new gasket. The pipeline stays connected throughout——no hot work, no cutting, no re-welding. That accessibility is the maintenance advantage of bolted-bonnet design over welded-bonnet design.

Yes——API 607 with metal-to-metal seats (Stellite 6). Flanged connections with RTJ gaskets maintain sealing through fire exposure alongside the valve body's metal seating. On flammable service pipelines, fire-safe certification is mandatory regardless of the connection type——flanged or welded, the seating system has to hold through fire.

1/2" or 1" flanged or threaded connection on the body——vented to atmosphere or closed drain depending on the process media. Hazardous media (H₂S, hydrocarbon, VOC) requires closed drain capture. Non-hazardous utility service vents to atmosphere through a needle valve. The bleed port size scales with the valve bore——larger bores use larger bleed ports to accommodate higher potential bleed flow rates under seat-failure conditions.