Metal Seated Triple Eccentric Butterfly Valve

2" - 48" (DN50 - DN1200)

Class 150 - 600 (PN 10 - 100)

API 609, ASME B16.34, ISO 15848 (low-leakage)

A216 WCB, A351 CF8M, A351 CF8, A182 F316 (forged for smaller sizes)

Metal-to-metal (Stellite 6 overlay on seat ring, hardened disc edge), fire-safe per API 607

Triple eccentric (shaft offset from centerline in three planes—axial, radial, angular), cam-action disc rotation eliminates seat friction during 90° travel, zero rubbing contact until final 2-3° of closing, metal seat rated for cyclic high-temperature service

Why Triple Eccentric Changes Everything

Most butterfly valves rub. The disc scrapes across the seat every time it opens and closes. Elastomer seats can tolerate that rubbing—they're soft, they deform, they recover. Metal seats don't. If you rub Stellite against Stellite every cycle, you grind the seal surface down until it leaks.

Triple eccentric geometry solves this at the structural level. The shaft is offset from the disc centerline in three planes—axial, radial, and angular. Those three offsets make the disc travel in a cam path. When you start opening the valve, the disc lifts off the seat immediately. It rotates freely through nearly the entire 90° stroke with zero contact against the seat ring. Only in the last 2-3 degrees of closing does the disc cam back into the seat and press into it for a seal.

That means the Stellite overlay doesn't get ground away cycle after cycle. Metal-to-metal seating holds up for thousands of cycles in high-temperature service where elastomer would have burned out after the first week. Continuous service at 350°C and above? Short-term exposure pushing past 500°C? This is where triple eccentric metal-seated valves earn their place.

When Fire Safety Isn't Optional

A fire on a petrochemical line isn't a hypothetical. It's a scenario you design for. Elastomer seats burn. They soften. They lose seal integrity while the line is still pressurized. A metal seat doesn't burn. It doesn't soften. It maintains mechanical seal contact through a fire event because the seating surfaces are hardened alloy, not rubber.

API 607 fire testing validates that. The valve gets burned, cooled, burned again—and it still holds its seal classification. Triple eccentric geometry helps here too, because the cam-action closing motion delivers consistent, repeatable seat contact force regardless of thermal expansion or distortion in the body.

ISO 15848 fugitive emission compliance rounds out the qualification package for refining and petrochemical applications. Regulators and plant operators both want the same thing—valves that don't leak process fluid to atmosphere, and don't leak more under fire conditions. This valve delivers on both counts.

What the Three Offsets Actually Do

Let's break it down plain. The axial offset moves the shaft behind the disc plane so the disc swings away from the seat on the downstream side during opening. The radial offset places the shaft off the pipe centerline so the disc cam-lifts uniformly. The angular offset tilts the shaft axis relative to the seat plane so the disc makes a progressively tighter seal in those final degrees of closing—more contact force, better seal integrity, no over-compression that could damage the seat.

All three work together. You can't get the same result with two offsets. Double eccentric reduces rubbing but doesn't eliminate it. Triple eccentric eliminates rubbing through the full stroke except for the sealing contact zone at closed position. That's the difference between a metal seat that lasts a season and a metal seat that lasts for years.

A: Yes. Metal-to-metal seating rated for continuous 350°C+ service covers saturated and superheated steam lines in Class 150-600 range. Select body material per steam chemistry—WCB for standard conditions, CF8M for corrosive steam condensate.

A: Gate valves work, but they're heavy, slow to stroke, and the wedging mechanism is prone to sticking after long periods in one position. Triple eccentric butterfly valves stroke in 90°, weigh less, and the cam-action geometry prevents seat binding. For frequent cycling in high-temperature service, butterfly is the better choice.

A: ISO 15848 defines fugitive emission testing and classification. Low-leakage means the valve meets stringent emission rate limits under defined test conditions—temperature cycles, mechanical cycles, and sustained pressure. For petrochemical plants subject to environmental emission regulations, this qualification is a compliance requirement, not a marketing label.

A: No. Stellite 6 overlay against hardened disc edge is a dry-metal seal pair. The cam-action geometry ensures the contact zone is limited to the final degrees of closing—no sustained sliding friction that would require lubrication. Seat integrity comes from geometry and material hardness, not from grease.

A: Manual lever (sizes 2"-6"), manual gear operator (8"-48"), electric actuator, pneumatic cylinder. The 90° quarter-turn stroke is compatible with all standard rotary actuators. Positioner and limit switch integration per project requirements.