China Double Offset Butterfly Valve Manufacturers, Suppliers and Factory

Double Offset Butterfly Valve

The double offset butterfly valve (also known as a double-eccentric butterfly valve) is a quarter-turn isolation and flow-control valve engineered for high-performance industrial pipelines. Its offset stem and disc arrangement lifts the disc off the seat immediately upon rotation, minimizing sliding contact and seat wear.

This double-eccentric geometry reduces operating torque while maintaining reliable bi-directional sealing across water, oil, gas, chemical, and power generation systems.

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Key Features and Working Principle

First Offset: The shaft axis is positioned behind the sealing plane of the seat.

Second Offset: The shaft axis is offset from the center axis of the valve and pipeline.

During opening, this dual-offset design causes the disc to swing clear of the seat in a cam-like motion. This action eliminates continuous friction on the sealing surface, lowers breakout torque, and extends seat service life.

Design Comparison: Concentric vs. Double Offset

Design / Selection Factor	Concentric Butterfly Valve	Double Offset Butterfly Valve
Stem & Disc Geometry	Rotates on the valve centerline	Double-eccentric (two offset axes)
Disc-Seat Contact	Continuous rubbing through 90-degree rotation	Disc lifts off seat immediately upon opening
Seating Friction & Wear	High friction; prone to premature wear	Minimal friction; extended service life
Operating Torque	Higher torque under pressure differential	Lower torque; allows smaller actuators
Pressure & Temp Rating	Generally low-to-medium range	Higher ratings (Class 150/300, PN10-PN40)
Primary Application	General utility isolation	Severe industrial service and high-cycle isolation

Technical Specifications & Material Selection

Parameter	Specification Options
Design Standards	API 609 Category B, EN 593, MSS SP-68
Nominal Sizes	DN50 – DN1200 / 2" – 48" (Larger sizes on request)
Pressure Ratings	ASME Class 150, Class 300 / PN10, PN16, PN25, PN40
Face-to-Face Standards	ISO 5752, EN 558-1 Series 20, API 609
Body Materials	Ductile Iron (EN-GJS-400), Cast Carbon Steel (WCB), Stainless Steel (CF8, CF8M, CF3M), Duplex (2205, 2507)
Disc Materials	Stainless Steel 304 / 316, Duplex 2205, Monel, Aluminum Bronze
Stem Materials	17-4PH, 17-7PH, SS420, SS316, Duplex 2205
Seat Materials	Soft: PTFE, R-PTFE, EPDM, NBR Metal: SS316 + Inconel / Stellite overlay (up to +400°C)
End Connections	Wafer, Lugged, Double-Flanged
Testing & Leakage	API 598, ISO 5208 (Zero-leakage options available)
Actuation	Manual Gearbox, Pneumatic Actuator, Electric Actuator

Industry-Specific Applications

Industry	Primary Service Conditions & Material Solution
Desalination & Seawater	Uses Super Duplex (2507) or Nickel-Aluminum Bronze to resist chloride pitting and velocity erosion.
Oil & Gas Processing	Features fire-safe testing, anti-static stems, and low fugitive emission packing for volatile hydrocarbons.
Chemical Handling	Pairs fluoropolymer seats (R-PTFE/PFA) with high-alloy trims for aggressive acids and alkalis.
Power Generation	Employs metal-to-metal seating for reliable operation in steam systems, blowdown lines, and cooling water.

Precision Manufacturing & Quality Control

Quality is integrated directly into every stage of production rather than relying only on final testing.

CNC Machining Precision:

Valve bodies, shaft bores, and disc profiles are processed on 5-axis CNC machines with tolerances held within +/-0.01mm.

Material Integrity (PMI):

100% Positive Material Identification (PMI) via Optical Emission Spectrometry on all alloy castings and stems.

Surface Polish:

Sealing surfaces on the disc are micro-polished (Ra < 0.4 um) to lower torque and prevent seat abrasion.

Stainless Steel Double Offset Flanged Butterfly Valve

Compliance & Testing Badges:

Quality System:

ISO 9001:2015

Pressure Equipment Directive:

CE / PED 2014/68/EU Module H

Fire Safety Certification:

API 607 / ISO 10497 (Select models)

Documentation:

MTR to EN 10204 3.1 supplied as standard; EN 10204 3.2 available upon request (SGS, TUV, BV).

FAQ

Q: What is the main structural advantage of a Double Offset Butterfly Valve over a Single Offset valve?

A: A single offset valve only moves the stem behind the seat plane. A double offset valve adds a second offset away from the pipeline centerline. This double-eccentric motion allows the disc to unseat faster without dragging across the sealing surface, significantly lowering wear and operational torque.

Q: How do I choose between a Soft Seat and a Metal Seat?

A: Choose Soft Seats (PTFE / R-PTFE) for applications requiring strict zero-leakage isolation at standard temperatures (up to 180°C–200°C). Choose Metal Seats (SS316 / Inconel / Stellite) for high-temperature systems (above 200°C up to 400°C), abrasive fluids, or fire-safe process requirements.

Q: Can these valves be installed in bidirectional flow lines?

A: Yes. Double offset butterfly valves are designed for bi-directional sealing. However, optimal sealing performance and lowest operating torque occur when pressure is applied in the preferred flow direction.

Q: Are your double offset valves suitable for automated control applications?

A: Yes. Equipped with standard ISO 5211 mounting pads, our valves seamlessly integrate with quarter-turn electric actuators or double-acting/spring-return pneumatic actuators for modulating or on-off control.

Q: What inspection documents are provided with the order?

A: Every shipment includes an EN 10204 3.1 Material Test Report (MTR) covering chemical composition, mechanical properties, and hydrostatic test results (API 598). Third-party inspections (SGS, TUV, BV) for EN 10204 3.2 certification can be arranged prior to dispatch.

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