Concentric vs Double Offset vs Triple Offset Butterfly Valves
Technical guide · Supreme Valves India · Updated 2026-10-28
Direct answer: Use concentric resilient-seated butterflies for water and utility PN10/PN16 or Class 150. Step up to double offset (high performance) for higher temperature, tighter shut-off or PTFE seats. Reserve triple offset for metal-seated, often fire-safe critical isolation. Body style (wafer/lug/flanged) is a separate decision from offset geometry.
Selection tree
| Type | Seat | Typical duty |
|---|---|---|
| Concentric | EPDM / NBR / Buna | Chilled water, seawater (with right materials), HVAC, PN16 water mains |
| Double offset | PTFE / RTFE / metal | Process Class 150/300, chemicals, higher temp than rubber |
| Triple offset | Metal laminated / solid | Critical isolation, steam/hydrocarbon, fire-safe specs |
How offsets work (buyer view)
- Concentric: disc centreline through pipe — seat rubs throughout stroke; soft seat OK.
- Double offset: shaft offset so disc cams into seat — less wear, enables PTFE and higher performance.
- Triple offset: adds a conical seating angle — metal-to-metal with minimal rub, torque rises.
WCB Class 150 RFQs
Many international BOQs say WCB body, Class 150 RF, SS316 disc, sometimes “STELLITED”, gear or limit switch — without saying concentric vs double offset. Ask: soft seat or PTFE/metal? Temperature? Fire-safe? That decides the geometry.
RFQ checklist
- Concentric / double / triple offset
- Wafer, lug or double flanged
- Seat and disc materials
- PN vs Class and flange standard
- Operator + switches
Start with WCB Class 150 butterfly RFQ; escalate geometry only with duty data.
Frequently asked questions
What is a concentric butterfly valve?
The disc rotates on a centreline through the pipe axis (zero offset). Soft elastomer seats (EPDM, NBR, etc.) provide shut-off for water and utility service, typically PN10/PN16 or Class 150.
When do I need double offset?
When temperature, pressure or cycle life exceeds soft concentric seats — high-performance butterflies with PTFE/RTFE or metal seats, often Class 150/300 process lines.
When is triple offset justified?
Metal-seated, often fire-safe critical isolation, higher temperature hydrocarbon and steam duties where rubbing must be minimised. Higher cost — specify only when the piping class demands it.