Lug Type Dual Plate Check Valve

Size: 2" - 48" (DN50 - DN1200)

Pressure: Class 150 - 600 / PN 10-100

Standard: API 6D, ASME B16.34, MSS SP-126 (dual plate check), AWWA C508 (waterworks)

Body Materials: A216 WCB, A351 CF8M, A351 CF8, ductile iron (GGG40)

Seat: Metal-to-metal or soft seated—dual plate check valves commonly use a combination: metal body seat ring + elastomer or PTFE seal on the plate edge for bubble-tight shutoff. Metal-to-metal plates available for high-temperature service.

Plates: Two semicircular plates (half-discs) hinged on a central hinge pin inside the body bore. Plates open by rotating away from the seat surface with forward flow—each plate swings to approximately 60-80° open position. A torsion spring on the hinge pin assists plate closure when forward flow velocity drops. Plates close in a spring-assisted, near-simultaneous motion.

Design: Lug body—threaded lug holes on both sides of the body flange. Lug format allows installation between two flanges with bolts through the lug holes, or as a line terminus with one flange blanked off. Short face-to-face dimension (API 6D pattern). Spring-assisted closing.

Compact and Fast-Closing — Two Half-Discs Beat One Full Disc

The dual plate design splits the check function between two semicircular plates instead of one full-disc swing. Each plate is lighter than a full disc. Each plate swings through a shorter arc to reach the closed position. That lighter mass and shorter travel translate directly to faster closing—roughly 0.2-0.5 seconds with spring assist, compared to 0.5-1.0 seconds for a gravity-closing full-disc swing check.

Faster closing means less reverse flow volume passes through the valve before it shuts. On pump discharge protection, that matters. Even a small reverse flow volume can spin the pump backward—reverse rotation causes mechanical damage to the pump impeller, bearings, and shaft. The dual plate check closes fast enough to limit reverse flow to a volume that won't establish sustained reverse rotation. A standard swing check closing in 0.5-1.0 seconds allows more reverse flow through the valve before the disc seats, and on some pump installations that extra volume is enough to start the pump spinning backward.

The torsion spring adds closing force beyond gravity. When forward flow velocity drops below the threshold that holds the plates open, the spring drives the plates toward the closed position even if there's no backpressure pushing them shut. That spring assist is essential for vertical installations—flow upward—where gravity doesn't help the plates close. In a vertical pipe, a gravity-closure swing check disc hangs open and relies entirely on reverse flow to push it shut. The dual plate spring closes the plates regardless of orientation.

Soft Seated for Bubble-Tight — Metal for High Temperature

Dual plate check valves commonly run a hybrid seating arrangement: metal body seat ring with an elastomer or PTFE seal on the plate edge. The metal seat ring provides structural integrity in the body bore. The soft seal on the plate edge compresses against the seat ring when the plates close, creating a bubble-tight shutoff that metal-to-metal seating can't consistently achieve at low backpressure.

If your process line needs zero leakage in the closed direction—chemical dosing lines, closed-loop heating systems, applications where even微量 backflow contaminates the upstream process—soft seated dual plates give you that bubble-tight seal under normal backpressure conditions. The elastomer or PTFE seal is replaceable during maintenance without re-machining the seat ring.

For high-temperature service where elastomer and PTFE seals degrade—steam above 400°F, hot oil service, fired heater feed lines—metal-to-metal plates are the specification. The plate edge contacts the metal seat ring directly, no soft seal. Shutoff isn't bubble-tight at low backpressure, but the metal seating survives the temperature where soft seals would harden, crack, or lose sealing compression.

Lug Body — Dead-End Service and Between-Flanges Installation

The lug body has threaded holes on both sides of the body flange. That lug format gives you two installation options that wafer-body check valves don't provide.

Option one: dead-end service. Install the valve at the end of a pipeline with one flange blanked off. The threaded lug holes on the blanked side accept bolts that secure the blind flange. Wafer-body check valves can't do this—they have no threaded holes and rely on being sandwiched between two flanges with through-bolts. If you need a check valve at a line terminus, lug is the format that works.

Option two: between-flanges installation without a separate spacer ring. The lug body bolts directly to the upstream and downstream flanges with bolts through the threaded lug holes. No spacer. No additional gaskets beyond the two flange-to-valve joints. Simple...