What is a triple offset butterfly valve?

It is a butterfly valve with three offsets: the shaft sits behind the seat plane, the shaft is off the pipe centreline, and the seat cone axis is inclined. Together they let the disc reach the seat without rubbing, so the valve can use a metal seat.

What is the difference between double offset and triple offset butterfly valves?

A double offset valve moves the shaft behind the seat and off centre, which cuts seat rubbing but still has some contact near closure and usually uses a polymer seat. The triple offset adds an angled seat cone, so contact happens only at closure and the seat can be metal.

What are the advantages of a triple offset butterfly valve?

Friction-free travel, a metal seat suited to high temperature, and a compact, light body compared with a gate or ball valve of the same size. The seal is torque-seated, so actuator sizing matters.

How do I calculate the operating torque of a triple offset butterfly valve?

Torque depends on seat design, size, differential pressure and service, so it comes from the manufacturer’s torque table rather than a general formula. Actuators are normally sized with a safety margin above that value. The partner factory torque data is to be confirmed.

What is a Stellite valve?

It is a valve whose seating surfaces are hard-faced with a Stellite cobalt-chromium alloy. The overlay resists wear, erosion and galling better than the base metal.

What is the difference between a wafer and a lug butterfly valve?

A wafer valve is clamped between two flanges by the flange bolts and cannot be used at the end of a line. A lug valve has threaded or drilled lugs so each flange is bolted to the valve independently, which allows dead-end service.

Draft page. The factory document pack for this page is still under review. Values marked “To be confirmed” have not been verified yet.

Triple offset butterfly valves

Butterfly valves · API 609

A triple offset butterfly valve adds a third, angular offset to the seat cone, so the disc seal touches the seat only at the moment of closing. This removes rubbing during travel and allows a metal-to-metal seat. Triple offset valves fall under API 609 Category B and are used for high temperature, abrasive and tight shut-off service.

Who makes this valve

Signed panel factories with API 609 in force3

How licences are checkedExpiry date in the API Composite List, not the “Active” flag

Registry checked8 Nov 2026Next check 8 Feb 2027

Manufacturer and licence no.Named in your quotation, with the registry link

We publish one number per API specification, never a factory-by-factory row: a row with its licence set and expiry year would point at a single registry entry. One RFQ is quoted by several panel factories, and each quotation names the manufacturer, its API licence number and where to verify it, so you can check the source before you order. How we check licences

How it compares

Concentric vs double offset vs triple offset butterfly valve geometry (general)
Feature	Concentric	Double offset	Triple offset
Offsets	None: shaft through disc centre	Shaft behind the seat plane and off the pipe centreline	Double offset plus an inclined conical seat axis
Seat contact during travel	Continuous rubbing	Reduced, near closure only	Contact only at final closure
Typical seat	Elastomer liner	PTFE or reinforced polymer; metal versions exist	Metal or laminated metal/graphite
API 609 category	Category A	Category B	Category B
Typical service	Water and low pressure utilities	Process service, moderate temperature	High temperature, steam, hydrocarbons, cryogenic

Specification range

Grades listed are common ASTM designations for this valve type. API 609 covers Class 150 to 600; the range offered by the partner factory is confirmed against its API 609 scope before this page goes live.

Triple offset butterfly valve specification: size × pressure class × ASTM grade
ASTM grade	Form	Sizes (NPS)	Pressure classes	End connections	Partner factory supplies
ASTM A216 WCB	Cast carbon steel body	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A351 CF8M	Cast 316 stainless steel	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A352 LCC	Cast low-temperature carbon steel	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A995 4A	Cast duplex 2205	To be confirmed	To be confirmed	To be confirmed	To be confirmed
ASTM A995 5A	Cast super duplex 2507	To be confirmed	To be confirmed	To be confirmed	To be confirmed

Pressure–temperature rating

API 609 Category B valves are rated to the pressure–temperature limits of ASME B16.34 for the body material, up to Class 600. The table shows group 1.1 Standard Class values at −29 °C to 38 °C. Seat material and the factory test may set a lower limit.

ASME B16.34 Standard Class, Group 1.1, −29 °C to 38 °C. Shell rating only; the valve rating can be lower because of seat and seal materials.
Pressure class	Max. working pressure (bar)	(psi)
Class 150	19.6	285
Class 300	51.1	740
Class 600	102.1	1,480
Class 900	153.2	2,220
Class 1500	255.3	3,705
Class 2500	425.5	6,170

Partner factory P-T curve for this valve: To be confirmed

Stellite seats and metal trim

Hard-facing the body seat with a cobalt-chromium alloy such as Stellite Grade 6 is a common way to resist erosion and galling in metal-seated valves. The overlay is applied by welding, so ask for the welding procedure specification and the hardness check.

Whether the partner factory offers a Stellite overlay, and on which sizes, is still to be confirmed.

Cryogenic triple offset valves

Triple offset valves are used in LNG and other cryogenic service with an extended bonnet and a low-temperature body material. A cryogenic type test, for example to BS 6364 or ISO 28921-1, is a separate qualification; no partner factory test report is published here yet.

Category A and Category B in API 609

API 609 separates butterfly valves into Category A, the concentric design with an elastomer or polymer seat, and Category B, the double and triple offset designs. Each category has its own requirements for seat leakage, testing and marking.

The category matters when you compare quotations. A Category A valve has a simpler body and seat, but its seat limits the temperature and the tightness class; a Category B valve is specified where a metal seat, fire-safe construction or a wide temperature range is needed.

Fire-safe and emissions requirements

A metal seat is not a fire-safe design by itself: in a fire the stem seal and the body gasket are usually the parts that fail first. API 607 and ISO 10497 test the assembled valve, so the certificate has to cover the seat, the stem seal and the body joint together.

ISO 15848-1 covers stem-seal emissions. Triple offset valves in hydrocarbon service are often specified with a tightness class and a qualifying cycle count from that standard.

No fire-test or emission-test certificate for a partner factory valve is published on this page.

Wafer, lug and double-flanged bodies

A wafer body sits between two pipe flanges and is held by the flange bolts. A lug body has threaded or drilled lugs on both sides, so each flange is bolted to the valve independently; that allows dead-end service. A double-flanged body has its own flanges and a longer face-to-face dimension.

Flange dimensions and drillings come from ASME B16.5 up to NPS 24, and API 609 gives face-to-face dimensions for butterfly valves. Check that dimension against the space in the line before you order, especially where the valve replaces another design.

Datasheet and drawings

Datasheet: To be confirmed

A datasheet, dimension drawing and STEP file will be published here, without factory branding, after the panel factory authorises them. Until then, ask for them in your RFQ.

Prices, lead times and minimum order quantities are quoted per enquiry against the datasheet you send; they are not listed on this page.

Frequently asked questions

What is a triple offset butterfly valve?: It is a butterfly valve with three offsets: the shaft sits behind the seat plane, the shaft is off the pipe centreline, and the seat cone axis is inclined. Together they let the disc reach the seat without rubbing, so the valve can use a metal seat.
What is the difference between double offset and triple offset butterfly valves?: A double offset valve moves the shaft behind the seat and off centre, which cuts seat rubbing but still has some contact near closure and usually uses a polymer seat. The triple offset adds an angled seat cone, so contact happens only at closure and the seat can be metal.
What are the advantages of a triple offset butterfly valve?: Friction-free travel, a metal seat suited to high temperature, and a compact, light body compared with a gate or ball valve of the same size. The seal is torque-seated, so actuator sizing matters.
How do I calculate the operating torque of a triple offset butterfly valve?: Torque depends on seat design, size, differential pressure and service, so it comes from the manufacturer’s torque table rather than a general formula. Actuators are normally sized with a safety margin above that value. The partner factory torque data is to be confirmed.
What is a Stellite valve?: It is a valve whose seating surfaces are hard-faced with a Stellite cobalt-chromium alloy. The overlay resists wear, erosion and galling better than the base metal.
What is the difference between a wafer and a lug butterfly valve?: A wafer valve is clamped between two flanges by the flange bolts and cannot be used at the end of a line. A lug valve has threaded or drilled lugs so each flange is bolted to the valve independently, which allows dead-end service.

Standards cited

BS 6364: Valves for cryogenic service: design requirements and a low-temperature type test. Edition quoted to: BS 6364:1984 (withdrawn by BSI in 2021 but still named in many LNG specifications).
ISO 28921-1: Isolating valves for low-temperature applications: design, manufacturing and production testing. Edition quoted to: ISO 28921-1:2022 (BS EN ISO 28921-1:2022).
API Std 609: Butterfly valves: Category A (concentric) and Category B (double and triple offset) for ASME Class 150 to 600.
API Std 607: Fire test for quarter-turn valves with non-metallic seats: a type test of the design.
ISO 10497: Fire type-testing requirements for valves: test procedure and acceptance criteria.
ISO 15848-1: Fugitive emissions: measurement, test and qualification procedures for valve stem seals, with tightness classes from a type test.
ASME B16.5: Pipe flanges and flanged fittings, NPS ½ to NPS 24.
ASME B16.34: Valves with flanged, threaded and welding ends: pressure–temperature ratings by material group and pressure class. Edition quoted to: ASME B16.34-2025.