Valve Comparison Guide
Triple Offset vs Double Offset Butterfly Valve — Which High-Performance Design?
Triple offset (TOV) vs double offset (high performance) butterfly valve: shut-off class, fire safety, temperature rating, API 609 categories and selection guide for critical service.
Overview
A triple offset butterfly valve has three geometric offsets: two lateral (as in double-offset) plus a third conical offset that makes the seating surface a cone. This means the disc lifts completely away from the seat in a cam-action motion — zero friction throughout the entire stroke until the final seating moment. Metal-to-metal shut-off.
DN100–DN1200, Class 150–600, WCB / CF8M / SS 316 seats, API 609 Category B
A double offset butterfly valve has two geometric offsets — the disc stem is offset from the centre of the disc and from the pipe centreline. This reduces seat friction during opening/closing. Soft (elastomeric or PTFE) or metal seats. Better than concentric type but does not achieve metal-to-metal shut-off.
DN50–DN900, Class 150–300, WCB / ductile iron / SS, PTFE or elastomeric seats, API 609 Category A
Pros & Cons
Triple Offset Butterfly Valve (TOV)
Double Offset (High Performance) Butterfly Valve
Triple Offset Butterfly Valve (TOV) vs Double Offset (High Performance) Butterfly Valve — Specification Comparison
| Parameter | Triple Offset Butterfly Valve (TOV) | Double Offset (High Performance) Butterfly Valve |
|---|---|---|
| Seat Type | Metal-to-metal (cone profile) | PTFE, elastomeric, or metal (softer) |
| Seat Friction | Zero (cam-action — lifts off before seating) | Reduced vs concentric, but still present |
| Shut-off Class | ASME Class VI at all temperatures | Class IV–VI (elastomeric); limited at high temp |
| Fire Safe | Yes — metal seats survive fire | Only if metal seats specified |
| Max Temperature | Up to 650°C (alloy steel seats) | 200–260°C (PTFE); higher with metal seats |
| API 609 | Category B (flanged) | Category A (wafer/lug) — Category B (flanged) |
| Bi-directional | Yes — standard feature | Possible but less reliable at high differential |
| Cost | Highest | Moderate |
| Seat Life | Very long — zero friction contact | Good but shorter at high-cycle service |
When to Use Each
Use Triple Offset Butterfly Valve (TOV) when:
Use Double Offset (High Performance) Butterfly Valve when:
Decision Guide
Choose a triple-offset butterfly valve for fire-safe service, high temperature (above 200°C), refinery or petrochemical critical isolation, and any application requiring metal-to-metal ASME Class VI shut-off at elevated temperature. Choose a double-offset (high performance) butterfly valve for general process service at Class 150–300, moderate temperatures, chemical service with PTFE seats, and any application where triple-offset is over-specified and cost is a consideration.
Frequently Asked Questions
What does 'triple offset' actually mean in a butterfly valve?
Can a triple-offset butterfly valve replace a gate valve?
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