Extended Stem Triple Offset Double Flange Hard Sealed Butterfly Valve

The extended stem triple offset double flange hard sealed butterfly valve is an industrial isolation valve designed for buried pipelines, underground utility vaults, tank farms and other installations where the handwheel or actuator must remain above grade while the valve body sits below ground level or inside confined pits. Manufactured by Trekre Valve in Wuxi, China, this double-flange triple eccentric butterfly valve combines metal-to-metal hard sealing with a custom-length extension stem so operators can open and close the valve from the surface without entering hazardous or flooded chambers. Worm gear manual drive is standard; bare stem ISO 5211 platforms accept electric multi-turn or pneumatic quarter-turn actuators for remote control on water supply, district heating, petrochemical and mining networks.

Extended stem butterfly valves solve a recurring field problem: the valve must be installed at the correct elevation for pipeline alignment, yet the operating device must be reachable for daily use and emergency shutdown. Trekre engineers the extension as a rigid, fully guided stem assembly rather than a simple pipe extension, maintaining concentricity and torsional stiffness across lengths from one metre to ten metres and beyond. The triple offset disc geometry lifts the sealing surface away from the seat during opening, reducing friction and operating torque on long-stem assemblies where stem deflection and packing friction would otherwise increase handwheel effort. Metal hard sealing handles high-temperature thermal oil, steam condensate, process gas and abrasive slurry media that destroy resilient soft seats over time.

Extended stem triple offset double flange hard sealed butterfly valve construction

Connection type: double flange (flanged ends both sides)

Structure: triple eccentric (triple offset) metal hard sealed disc with extension stem assembly

Size range: NPS 2″ to 48″ (DN50 to DN1200)

Pressure rating: PN10, PN16, PN25, PN40; ANSI Class 150/300 where cross-referenced

Body material: WCB carbon steel, WC6/WC9 alloy steel, CF8/CF8M austenitic stainless steel, LCB low-temperature carbon steel

Disc material: stainless steel 304/316 or alloy matched to body and media, with hardened sealing edge

Seat: metal seated — Stellite-faced integral body seat, replaceable metal ring or multi-layer laminated hard seal

Extension stem: carbon steel or stainless steel stem tube with internal stem rod, guide bearings and adjustable packing gland; length per site survey

Operation: worm gear manual standard; bare stem ISO 5211 platform; electric multi-turn or pneumatic quarter-turn optional

Seal direction: bidirectional or unidirectional per pipeline specification

Design standard: GB/T 12238, API 609 Category B, EN 593 where applicable

End flange: GB/T 9113, HG/T 20592, ANSI B16.5 Class 150/300, EN 1092-1

Face-to-face: GB/T 12221, EN 558 Series 13/14, API 609 short/long pattern

Testing: GB/T 13927, API 598, EN 12266-1 shell and seat leakage class

Temperature range: -29°C to 425°C (body, seat, stem packing and extension seal limited by material selection)

Triple offset geometry and extension stem engineering

Triple offset design positions the disc rotation axis behind and beside the seat centreline so the sealing ring contacts the seat only in the final degrees of closing travel. This camming action creates the sealing load without sliding friction across the full 90-degree stroke, which is especially important on extended stem valves where cumulative packing drag and stem side load can otherwise prevent reliable shut-off. Trekre machines the offset angles to maintain consistent seat contact pressure from DN50 through large-bore DN1200 sizes, with disc edge hardening matched to the seat overlay for long service life on cycling duty.

The extension stem assembly consists of an outer protective tube, internal torque-transmitting stem, intermediate guide supports for spans exceeding three metres, and a weatherproof packing flange at the upper end. Guide bushings prevent stem whip under rapid operation and keep the disc square to the seat after years of underground service. The lower coupling connects to the valve stem through a verified key or spline interface; the upper end terminates at the worm gear input or actuator mounting flange. For buried service, the tube wall thickness and external coating system are specified to resist soil loading, groundwater and stray current corrosion. Customers specify total stem extension, floor-to-centreline dimension and orientation of the operating head relative to the pipeline axis at order stage.

Applicable working conditions and industries

Extended stem triple offset hard sealed flange butterfly valves serve municipal water transmission mains installed in buried valve chambers, district heating return lines where operators cannot access the valve body, mining dewatering headers in underground galleries, petrochemical tank dike isolation, and power plant circulating water pits. The metal hard seal tolerates higher temperature and velocity than rubber-lined alternatives, making the valve suitable for thermal oil circulation, high-pressure steam condensate isolation and process gas lines carrying light hydrocarbons or inert gas. Triple offset shut-off performance meets bubble-tight requirements on clean media and controlled leakage classes on dirty or high-velocity flow when specified with appropriate seat overlay and actuator sizing.

Underground and buried installations benefit from the double flange body because each pipeline spool bolts independently, simplifying removal for maintenance without disturbing the opposite line. The extension stem eliminates the need for valve pits large enough to accommodate an operator at body level, reducing civil construction cost and improving safety in confined or flooded spaces. Worm gear drives with self-locking reduction ratios hold the disc position without continuous operator input; optional position indication and lockable handwheel covers support padlock security on public utility networks. Electric actuator packages with buried conduit entries and torque-limiting controls integrate with SCADA systems for remote isolation during pipeline breaks or scheduled maintenance.

Product parameters summary

Model series: extended stem triple offset double flange hard sealed butterfly valve

Nominal diameter: DN50–DN1200 (NPS 2″–48″)

Nominal pressure: PN10/PN16/PN25/PN40, Class 150/300

Body: WCB, WC6, WC9, CF8, CF8M, LCB

Disc and seat: stainless steel or alloy with Stellite or laminated metal hard seal

Extension stem length: 1000 mm to 100000 mm (custom per drawing)

Drive: worm gear manual, bare stem ISO 5211, electric or pneumatic actuator

Standards: GB/T 12238, API 609, EN 593, HG/T 3708

Leakage class: API 598, EN 12266-1 Rate A or project-specified

Selection and ordering checklist

Confirm medium composition, design temperature and pressure, nominal diameter, flange standard and pressure class, extension stem total length and floor-to-pipe-centreline dimension, drive type and required operating torque, seal direction, leakage class, external coating for buried service, and whether the valve must comply with a project-specific inspection and test plan. Trekre Valve provides technical datasheets, material certificates, pressure test reports and dimensional drawings for EPC approval. Contact the factory with pipeline isometric details and chamber dimensions so the extension stem span, guide support spacing and packing arrangement are engineered for your site conditions rather than selected from a generic catalogue length.

Anti-corrosion measures for buried extended stem assemblies include epoxy coal tar or fusion-bonded epoxy on the body exterior, stainless steel stem tubes for aggressive soil, and sacrificial anode or cathodic protection interfaces where project specifications require them. Upper packing sets use graphite or PTFE-impregnated fibres rated for the operating temperature band, with lantern rings and flush connections available for fugitive emission monitoring on petrochemical duty.

For global distributors and equipment manufacturers sourcing from China, this extended stem triple offset double flange hard sealed butterfly valve delivers a proven isolation solution for buried and inaccessible installations where soft-seated or non-extended designs cannot meet temperature, media or operational access requirements. Request a quotation with your complete duty specification and the Trekre engineering team will confirm body material, seat overlay, stem extension layout and actuator interface before production release.