Triple Offset Butterfly Valves for Hydrocarbon Isolation: How They Work and When to Use Them

Technical guide · Supreme Valves India · Updated 2026-10-25

A triple offset butterfly valve (TOV or TOBV) gives metal-to-metal, torque-seated shut-off in a quarter-turn valve that is far shorter and lighter than a gate valve of the same size and class. That combination is why it is specified for hydrocarbon isolation, steam, high-temperature and fire-safe duties where a rubber-lined butterfly valve would not survive.

How the three offsets work

1. Shaft behind the seal. The shaft is set behind the sealing plane, so the seal is continuous all the way round with no interruption at the shaft.
2. Shaft off-centre. The shaft is offset from the pipe centreline, so the disc swings away from the seat as it opens.
3. Inclined conical seat. The seat is a cone whose axis is tilted from the pipe axis. The seal ring meets the seat only in the final degrees of closing and lifts off immediately on opening.

The result is a cam action with no rubbing during stroke. Sealing comes from torque pressing the seal ring into the conical seat, not from interference with a rubber liner. Concentric (rubber-lined) and double offset (high-performance) valves rely on some seat contact through part of the stroke; the triple offset design avoids it completely.

Seal designs

• Laminated seal ring: alternating layers of stainless steel and graphite. Tolerates small distortion and gives tight shut-off; the most common design.
• Solid metal seal ring: for high temperature, abrasive or high-cycle service, and where graphite isn't acceptable.
• Seat: machined into the body, often with a stellite or other hard-faced overlay; or a replaceable seat ring.

Where triple offset valves are used

• Hydrocarbon process and product lines, tank farm isolation, refinery units.
• Steam and condensate, boiler and turbine auxiliaries.
• Emergency shutdown and remotely operated shut-off valves (ROSOV), with fire-safe certification and fail-safe actuators.
• High-temperature gas and flue duties, and cryogenic service in special designs.

Advantages over a gate valve

• Much shorter face-to-face and lower weight, especially from NPS 8 upwards.
• Quarter-turn operation, easy to fit with pneumatic or electric actuators.
• No seat cavity to trap fluid or solids.
• Bubble-tight shut-off is achievable with laminated seals when tested to the specified class.

Points to check before specifying

• Preferred direction. Many valves have a preferred sealing direction with a higher rating. Specify the expected pressure direction.
• Shut-off class. State the test standard and leakage rate, for example API 598, ISO 5208 Rate A, or a specific allowable leakage.
• Fire-safe. For hydrocarbons, ask for an API 607 or ISO 10497 fire test certificate covering the design, size and class.
• Torque. Seating torque is high relative to concentric valves. Size actuators for seating and unseating torque with margin, at the maximum differential pressure.
• Disc clearance. Check the disc swing against the pipe bore, especially with heavy-wall or lined pipe.
• Standards. API 609 Category B covers offset butterfly valves; ASME B16.34 sets body ratings.

What to include in an enquiry

Size, class, body style (wafer, lug or double flanged), body, disc and seal materials, maximum shut-off pressure and direction, temperature, shut-off class, fire-safe requirement, and operator with fail position.

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