Wafer Double Eccentric Butterfly Valve

2" - 48" (DN50 - DN1200)

Class 150 - 300 / PN 10-40

A216 WCB, A351 CF8M, A351 CF8, ductile iron (GGG40)

Resilient elastomer (EPDM/NBR/Viton) on disc edge, or PTFE/modified PTFE for higher temperature; optional metal seat ring with Stellite overlay for high-temperature configurations

Double eccentric (high-performance)—shaft offset from disc center in two planes (axial + radial). Disc lifts off seat during initial rotation, reducing seat friction and extending cycle life. Wafer body—sandwich between pipeline flanges.

API 609, ASME B16.34, EN 593

The Gap That Needed Filling

Centerline butterfly valves seal well at low pressure. They're cheap, they're simple, they work. But push the pressure toward Class 300 and the disc starts deforming under differential load. Push the temperature past what elastomer can tolerate and the liner degrades. Push the cycle count into the thousands and the rubbing friction between disc and seat starts wearing out the elastomer.

Triple eccentric metal-seated valves handle all of that. They seal at Class 600, they handle 350°C+, they cycle metal-on-metal without degradation. They also cost considerably more, and for many applications between centerline limits and triple eccentric territory, they're overkill.

That's the gap. Double eccentric—what API 609 calls "high-performance butterfly valve"—fills it. Two shaft offsets move the disc off the seat centerline. The disc cam-lifts during the first degrees of rotation instead of sliding across the seat surface. Reduced rubbing. Extended seat life. Typically 3-5 times more cycles before seat replacement compared to concentric designs. Pressure handling up to Class 300. Temperature capability up to approximately 250°C with PTFE or modified PTFE seats. Metal seat option with Stellite overlay for moderate high-temperature service. All in a wafer body that sandwiches between pipeline flanges—the most space-efficient installation format available.

Two Offsets, Real Results

The axial offset places the shaft behind the disc centerline plane so the disc swings away from the seat on the downstream side during opening rotation. The radial offset positions the shaft off the pipe centerline so the disc lifts uniformly as it begins to rotate. Together, these two offsets create a cam-action motion—the disc separates from the seat in the first degrees of opening instead of dragging across it.

That reduced contact friction is the key benefit. On a concentric valve, the disc scrapes across the elastomer liner through the entire 90° stroke. Every cycle scrapes the seat. After enough cycles, the liner wears thin, loses compression against the disc edge, and starts leaking. On a double eccentric valve, the disc only contacts the seat in the closed position and during the final degrees of closing. The rest of the stroke is frictionless. Seat material survives longer. Cycle intervals between maintenance stretch out. Plant uptime improves.

The elastomer seat sits on the disc edge instead of in the body bore—that's another difference from centerline construction. Disc-edge seating gives you a tighter, more defined seal contact zone. PTFE and modified PTFE seats on the disc edge push the temperature ceiling higher than body-bore elastomer liners. Metal seat rings with Stellite overlay on the disc take you into moderate high-temperature territory without jumping to triple eccentric pricing.

Wafer Format Keeps It Lean

Wafer body means the valve sandwiches between two pipeline flanges. Through-holes in the body flange ears. Bolts pass through the valve and thread into the pipeline flange nuts on both sides. No valve flanges of its own. The pipeline flanges carry the bolt load. The valve sits in the gap between them.

That makes the wafer double eccentric butterfly valve the most compact high-performance quarter-turn valve you can install. Face-to-face dimensions follow API 609 short pattern or long pattern. The short pattern fits the same face-to-face space as a centerline wafer valve. The long pattern gives you a longer body bore for improved flow characteristics at higher pressure. Either way, the installation footprint is smaller than a flanged gate valve, smaller than a flanged ball valve, and the weight is lower too.

Cost sits between centerline and triple eccentric. You pay more than a centerline valve for the double offset geometry and the higher pressure/temperature capability. You pay less than a triple eccentric valve because you don't need three offsets and metal seating isn't mandatory. For process lines running Class 150-300 at temperatures that exceed elastomer liner comfort but don't demand full metal-to-metal fire-safe seating, this is the right valve.

A: API 609 categorizes butterfly valves as Category A (centerline/concentric) and Category B (offset/high-performance). Double eccentric valves fall into Category B because the shaft offsets move the disc off the seat centerline, creating cam-action rotation. Category B covers higher pressure classes, reduced seat friction, and extended cycle life compared to Category A.

A: Modified PTFE seats on the disc edge handle temperatures up to approximately 250°C continuous, which covers many saturated steam applications in the Class 150-300 range. For superheated steam or temperatures above 250°C, specify the metal seat option with Stellite overlay, or move to a triple eccentric metal-seated valve.

A: Wafer format keeps cost and weight down. If your application requires one-side isolation, dead-end service, or line-blanking capability, specify the lug body version. For standard inline isolation where both pipeline flanges remain connected, wafer is the standard and most cost-effective choice. Both body formats use the same double eccentric internals.

A: Resilient elastomer seats on double eccentric valves typically deliver 3-5 times more cycles than equivalent seats on concentric valves, because the cam-action geometry reduces seat friction during rotation. Exact cycle life depends on media, temperature, pressure differential, and stroke frequency. In standard water and light-process service, expect 50,000+ cycles before seat intervention. In more demanding conditions, plan for earlier scheduled maintenance.

A: When your application requires Class 300+ sustained pressure, metal-to-metal fire-safe seating per API 607, continuous service above 250°C, or ISO 15848 fugitive emission compliance for petrochemical service. Double eccentric handles the middle ground—Class 150-300, moderate temperature, resilient or PTFE seating. Triple eccentric handles the demanding end—Class 600, high temperature, metal seating, fire-safe qualification.