Triple-Offset Butterfly Valves: Zero-Leakage Isolation

Triple-offset butterfly valves (TOBV) use three geometric offsets to achieve metal-to-metal, zero-leakage Class VI shut-off without friction between seat and disc during operation. They are replacing ball and gate valves in many high-pressure applications.

The Three Offsets

First offset: stem axis behind disc centerline—eliminates interference on openingSecond offset: stem axis eccentric to pipe centerline—lifts disc away from seatThird offset: seat cone axis tilted relative to pipe axis—disc contacts seat only at the last degree of closing

Torque and Seating

The oblique seating geometry means seating force is perpendicular to the seat surface, not a sliding action. This eliminates friction-induced wear and allows metal-to-metal sealing with repeatable Class VI performance throughout valve life.

Materials and Temperature Range

TOBV discs and seats use Stellite-overlaid or stainless steel hard-faced surfaces. They operate from cryogenic temperatures to +593 °C. The compact face-to-face dimension (per API 609) reduces piping spool length compared to full-bore ball valves.

Applications and Sizing

Cryogenic LNG service, high-pressure steam, refinery crude unit, and power plant main steam lines use TOBVs. Cv values are available from manufacturers for sizing. Actuator sizing must account for seating torque at maximum differential pressure.

Specify API 609 Category B for fire-safe TOBVConfirm seat material for temperature and erosion resistanceSize actuator with 25% torque margin above calculated seating torquePerform leakage test per API 598 or ISO 5208 after installation