Double vs Triple Offset Butterfly Valves: Differences & Selection

For a purchase decision, compare the proposed configurations against one common duty sheet. Ask the supplier to identify the geometry on a sectional drawing before comparing materials, tests, installation and maintenance. This avoids treating a design label as proof that a valve meets the whole project specification.

In a double-offset arrangement, the shaft is displaced from the seat plane and pipeline centreline. Bray's McCannalok manual describes cam action lifting the disc from its seat during opening. Emerson's triple-offset explanation adds an inclined sealing cone to the two shaft offsets, intended to avoid rubbing during rotation. These are design principles, not a guarantee of wear-free operation in every service.

Review the actual drawing and operating instructions. The catalogue word 'high-performance' is not sufficient to identify a particular geometry. KEHUA's high-performance series should be reviewed on its own offered drawing; this guide does not rename that series as a verified double-offset model.

No. Geometry and seat construction are separate specifications. Bray's McCannalok range includes a metal-seated option, illustrating why double offset should not be used as a synonym for soft seated. For any proposal, request a component-level material list rather than relying on a broad seat label.

For KEHUA's listed triple-offset metal-seated series, ask what the offered sealing assembly actually contains. Confirm the body, disc, shaft, seat, seal ring, packing and gaskets. Where a ring is laminated or has inserts, identify their materials and limitations. A metal seat description does not establish that every component is all-metal or suitable for the same temperature.

Start with the medium and the complete operating envelope. Water service still needs a review of chemistry, solids and operating cycles. Steam service needs temperature and cycling data. Oil and gas duties need composition and any project-specific sealing, emissions or fire-test requirements. These are questions for technical review, not blanket approvals for either geometry.

Supply normal and design pressure and temperature, maximum closed-valve differential pressure, upset conditions and required pressure direction. Where ASME B16.34 is specified, confirm its applicability and the contract edition with the supplier. The standard's public scope covers pressure-temperature ratings, materials and testing, among other topics; a design label cannot substitute for the offered model's records.

For solids, abrasive media or corrosive service, request a documented suitability assessment of the wetted and sealing materials. For throttling, provide flow cases and ask for sizing and control review. Do not infer control suitability from an isolation-valve description or from the number of offsets.

No universal guarantee follows from the name. Make leakage acceptance a written procurement requirement: identify the applicable test standard and edition, test medium, pressure, duration, direction and acceptance criterion. Request evidence for the exact supplied configuration and distinguish seat leakage from leakage to atmosphere.

If shutoff is required with pressure from either side, state that explicitly and obtain the supplier's supported limits for both directions. Do not transfer another manufacturer's test result, certification or marketing claim to a KEHUA valve. Also separate factory acceptance testing from any promised performance in the actual process conditions.

Ask for valve torque data at the specified duty, the actuator sizing basis, minimum available supply and required failure position. Review seating and unseating requirements as well as running torque. Agree travel stops, setting instructions and any commissioning checks; avoid an unsupported assumption that either design always needs a smaller actuator.

Offset geometry is independent of body attachment: compare the wafer butterfly valve, lug butterfly valve or flanged butterfly valve series against the piping layout. Confirm the mating flange, face-to-face length, pipe bore, disc clearance and installation envelope on the drawing. If downstream piping may be removed, obtain separate end-of-line approval. For maintenance, ask for access requirements, replaceable components, spare-part identification and permitted service procedures.

Send one duty sheet to each supplier so that quotations can be compared without hidden differences. Record exceptions and obtain engineering approval before ordering.