Expanding Plug Valve-Full Bore

2" – 36" (DN50 – DN900)

Class 150 – 600 / PN 10-100

API 6D, API 599, ASME B16.34, API 607 (fire-safe available)

A216 WCB, A217 WC6/WC9, A351 CF8M, A351 CF8

Metal-to-metal, expanding plug mechanism — central core + expandable sealing elements for DBB sealing against full-diameter seat faces.

Full-bore (full-port) flow passage. Body bore at the seat area matches nominal pipe diameter. Piggable when open. Zero pressure drop in open state.

Everything the Venturi Gives You, Plus an Open Bore

The full-bore expanding plug valve delivers the same DBB function as the venturi version — two independent sealing boundaries in a single valve body, expandable slips that seal simultaneously against upstream and downstream seat faces, a built-in bleed port between the seats. Same isolation capability. Same single-valve DBB package.

What's different is the bore. Full bore means the body passage at the seat area matches the pipeline diameter. No constriction. No reduced cross-section. When the valve is open, the flow passage is the same diameter as the pipe on both sides.

Two things change when you open up the bore.

First: pigging. Pipeline pigs, cleaning tools, scraping tools, inspection pigs — they all need a full-diameter bore to pass through. A venturi constriction blocks the pig. Full-bore passage lets it go. If your pipeline specification requires piggable valves at isolation points, the full-bore expanding plug is the only plug valve design that gives you DBB isolation and piggable flow in one body.

Second: pressure drop. In continuous-flow applications where the valve stays open most of the time, the venturi constriction adds a permanent pressure loss. Every hour, every day, that loss is there. Full-bore passage eliminates it. Open bore matches the pipe diameter, flow goes through unobstructed, and your pump or compressor doesn't have to compensate for a restriction that shouldn't be there.

The Mechanical Cost of a Full-Diameter Seat

Full-diameter seat faces are larger. The expanding slips have to seal against a seat circumference that matches the full pipe diameter — not a reduced venturi diameter. More circumference means more expansion travel, larger sealing elements, and a heavier mechanism.

At 12 inches and below, the difference is modest. The full-bore mechanism is still compact enough to be straightforward. At 24 inches and 36 inches, the expanding elements are pushing outward against a seat circumference two or three feet across. The mechanism gets bigger, more complex, and more expensive to manufacture.

That's the tradeoff. Full bore gives you piggable flow and zero pressure drop. It costs more — especially at large sizes — because the expanding mechanism has to work against a larger seat. When your specification demands pigging or zero open-state pressure drop, the cost is justified. When it doesn't, the venturi version gives you the same DBB function for less money and with a simpler mechanism.

Transmission pipeline isolation at stations where pigs run through. That's the primary application. Pipeline operators run pigs regularly for cleaning, inspection, and integrity verification. Every isolation valve on a piggable section has to let the pig pass. A venturi valve blocks the pig — the crew has to remove the valve or install a bypass every time they run one. Full-bore expanding plug valves eliminate that problem.

Continuous-flow isolation points — meter stations, compressor station block valves that sit open for months and only close for maintenance — also benefit from full bore. The open-state pressure drop through a venturi valve accumulates over time. In continuous service, eliminating that drop saves pumping energy and reduces operating cost.

Fire-safe configurations are available. API 607 testing confirms both sealing boundaries hold after fire exposure, and the full-bore passage doesn't compromise fire-test performance.

A: Standard cleaning pigs and inspection pigs pass through the full-bore open passage. Verify pig dimensions with the valve manufacturer — some expanding plug designs have minor internal features that may affect specific pig types. In general, full-bore expanding plug valves are piggable for standard pipeline pigging programs.

A: Larger seat circumference requires larger expanding sealing elements and more expansion travel. The mechanism components — slips, wedges, core, seat faces — all scale with the bore diameter. At 24"–36", the mechanical package is substantially larger than the equivalent venturi design.

A: Yes. The expanding mechanism creates two independent sealing boundaries against the full-diameter upstream and downstream seat faces. DBB function is the same — the only difference is the seat diameter the slips seal against.

A: That's exactly where full bore delivers its pressure-drop advantage. The venturi version adds permanent flow restriction during those long open periods. Full bore eliminates that restriction. For isolation valves that rarely close but need DBB when they do, full bore is the better choice.

A: 2" through 36" (DN50 through DN900). The most common sizes in pipeline service are 6" through 24". 30" and 36" are available for large-diameter transmission pipeline isolation but carry significant cost premiums due to the size of the expanding mechanism at those diameters.