The worm gear hard seated lug type butterfly valve is a triple eccentric lug-style isolation valve engineered for demanding process lines that require metal-to-metal or enhanced metal sealing, fire-safe performance and reliable quarter-turn shut-off under elevated temperature and pressure. Manufactured by Trekre Valve, this hard seated lug butterfly valve combines a three-offset disc geometry with threaded lug bolt holes on each side of the body for installation between compatible pipeline flanges. Any dead-end or single-flange duty requires the documented rating, permitted pressure direction and approved bolting arrangement for the exact valve model, size and configuration. Worm gear operation delivers controlled torque multiplication for large bore sizes while keeping operator effort predictable on frequently cycled or infrequently operated isolation points.
Triple eccentric design positions the disc rotation axis behind the body centreline and behind the sealing plane, creating a conical closure path where the disc lifts away from the seat at the first degrees of opening instead of sliding across it. That geometry minimises friction between the hard seat and disc sealing surface, reduces operating torque and extends service life on metal seated applications where resilient liners would not survive temperature or media conditions. At final closing, the disc contacts the seat only at the last moment of stroke, ensuring uniform sealing load without unnecessary wear — a principle that makes triple eccentric lug butterfly valves preferred for high-cycle isolation on gas headers, compressor suction lines and thermal utility systems.
Worm gear hard seated lug type butterfly valve construction
Connection type: lug type (threaded lugs; single-flange or dead-end use only within the documented rating and approved installation arrangement)
Structure: triple eccentric (triple offset) hard seated disc
Size range: NPS 2″ to 72″ (DN50 to DN1800)
Pressure rating: ASME Class 150, 300, 600, 900 and 1500 (size and material dependent)
Body material: WCB carbon steel, CF8/CF8M austenitic stainless steel, WC6/WC9 chromium-molybdenum steel, duplex stainless and nickel-base alloy options
Disc material: stainless steel with surface hardening, or alloy construction matched to body
Seat: metal seated (Stellite or body integral), multi-layer hard seal, elastic metal seal or PTFE/ RPTFE ring on metal base for hybrid sealing
Operation: worm gear and worm shaft (manual gear operated); electric, pneumatic or hydraulic actuators optional
Seal direction: unidirectional or bidirectional sealing selectable per application
Design standard: API 609 Category A/B, MSS SP-67, ASME B16.34
Face-to-face: API 609
End flange: ASME B16.5
Testing: API 598 shell and seat test
Fire-test requirement: confirm any API 607 qualification against a traceable test report applicable to the supplied valve configuration.
Temperature range: -196°C to 600°C (material and seat limited)
Sealing philosophy and fire-safe performance
Hard seated lug butterfly valves from Trekre are built around a geometric sealing concept where the seal ring meets the seat at the instant of final closure, avoiding the continuous rubbing typical of concentric or single-offset designs. Metal sealing can rely on integral body seat with overlay alloy, Stellite-faced seat rings or a composite ring that combines PTFE flexibility with metal backup for low-leakage duty. Specify the required sealing direction separately from any single-flange or pipe-end isolation duty. Confirm both requirements for the exact supplied valve; one does not establish the other.
Where fire-test qualification is required, request the applicable API 607 test report and confirm that it covers the supplied design, materials, pressure class and size within the report’s documented scope. Do not infer fire-test qualification, retained isolation performance or suitability for a fire-exposure duty from a metal seat, packing description or a standard reference alone.
Lug type installation advantages
Lug bodies carry tapped bolt holes on each side, allowing the valve to be bolted to one flange while the opposite pipeline remains undisturbed — a practical benefit for maintenance on long headers, tank farm manifolds and building risers. Do not infer dead-end service or permission to remove downstream piping from the lug body alone. Confirm the exact valve’s single-flange rating, permitted pressure direction, bolting arrangement and isolation procedure before approving that duty. For large bore water supply and power plant cooling systems, lug connection also distributes flange loads evenly and resists pipeline thrust when installed with proper anchor points.
Because triple eccentric lug butterfly valves cost more than concentric gear-operated lug valves, engineers often reserve them for elevated temperature, higher pressure or abrasive media where metal sealing and low torque are mandatory. For low-pressure ambient water, a concentric resilient seated lug valve may suffice; for steam, thermal oil, acidic gas or high-cycle hydrocarbon service, the hard seated triple offset lug type remains the durable choice.
Worm gear operation and actuator interface
The supplied worm gear operator multiplies handwheel input torque through a precision worm and worm wheel pair, enabling confident closure on large diameter discs without excessive operator force. Gear housings are sealed against ingress, with position indication and optional locking devices for tamper-evident isolation. Where remote operation is required, the same valve body accepts electric multi-turn actuators, pneumatic scotch-yoke quarter-turn units or hydraulic operators sized to breakaway and running torque curves derived from seat material and differential pressure.
ISO 5211 mounting pads can be integrated on selected sizes so quarter-turn pneumatic or electric actuators bolt directly to the valve, reducing adapter hardware and alignment error. Trekre engineers size operators using calculated torque with safety factors for seat friction, differential pressure and media film coefficient, ensuring reliable closure on emergency shutdown and block-and-bleed sequences.
Product parameters summary
Structure: triple eccentric lug body with worm gear operator
Nominal diameter: DN50–DN1800 (2″–72″)
Pressure class: Class 150 / 300 / 600 / 900 / 1500
Body: WCB, CF8, CF8M, WC6, WC9, duplex or alloy steel
Disc: stainless or alloy with hardened sealing edge
Seat: metal seated, multi-layer, elastic metal or PTFE-composite
Operation: worm gear manual; electric, pneumatic or hydraulic optional
Connection: lug to clamp or double-flange pattern per API 609
Design standard: API 609, MSS SP-67, ASME B16.34, ASME B16.5
Temperature range: -196°C to 600°C (configuration limited)
Testing: API 598; any API 607 fire-test qualification requires an applicable documented test report
Typical applications and industries
Petrochemical cracking units, catalytic reformers and intermediate product transfer lines requiring metal seated isolation
Natural gas gathering, city gate stations, compressor stations and pipeline sectionalising valves
Metallurgical plant cooling water, blast furnace gas and coke oven utility headers
Power plant steam extraction, condenser cooling water and auxiliary fuel gas systems
Water treatment sludge lines, filter isolation and high-pressure backwash manifolds
Food and pharmaceutical utility steam, CIP circuits and process water where metal seats resist CIP chemicals
Advantages of Trekre hard seated lug butterfly valves
Triple eccentric geometry delivers low operating torque and extended seat life on metal sealed applications where bubble-tight shut-off must be maintained after thousands of cycles. For maintenance in dead-end or sectionalising layouts, confirm the documented single-flange rating and the approved isolation and bolting arrangement for the exact supplied valve. Fire-safe seat and packing design adds an essential layer of protection in hydrocarbon and gas services. Material options from carbon steel through duplex and nickel alloys cover corrosive, high-temperature and cryogenic extremes within one product family. Worm gear operators provide dependable manual control on large bore valves while preserving a straightforward path to automated actuation when project specifications evolve.
Every worm gear hard seated lug type butterfly valve is manufactured and inspected at our Wuxi, China facility with hydrostatic shell and seat testing per API 598, material traceability and dimensional verification against API 609 face-to-face tables. Request technical datasheets, torque data and material certificates for your project specification — Trekre Valve supports EPC contractors, stockists and end users with selection guidance, custom trim packages and consistent supply from a dedicated industrial valve factory.
Frequently Asked Questions
Does a hard-seated lug valve automatically allow downstream pipe removal?
Request the documented end-of-line rating and approved bolting arrangement for the exact size and configuration. Neither the lug body nor the metal-seat description establishes that duty by itself.
What shutoff information should I include for a metal-seated valve?
State the medium, operating conditions, differential pressure and required leakage acceptance and test conditions. Ask for confirmation of the selected seat construction and applicable test evidence rather than relying on a general hard-seat description.
How can I check whether I can reach and operate the handwheel?
Send the installation orientation and available space around the valve. Request the actual gearbox assembly drawing and operating requirements before fixing the layout.