Triple Offset Butterfly Valves

What Is a Triple Offset Butterfly Valve?

In conventional butterfly valves the disk rubs against the seal as it rotates, which causes wear and leakage, particularly in metal-seated designs. In a triple offset design the shaft is offset from the disk center and from the pipe axis, and the third offset comes from the conical geometry of the sealing surface. Thanks to these three offsets, the disk moves without friction during opening and closing and touches the seat only in the final position.

Sealing is achieved as actuator torque presses a laminated metal seal ring onto a hardfaced seat integrated into the body. The resilient metal ring distributes the seating force evenly around the precisely machined seat circumference. The valve can therefore seal in both directions without visible leakage in water and air tests.

The all-metal, fire-resistant construction makes triple offset valves suitable for isolation points where high temperature, high pressure and fire safety matter. With the right trim, the same valve can also be used for process control. Its short face-to-face dimension and low weight make it a more compact isolation solution than gate or ball valves on large lines.

How Does the Triple Offset Geometry Work?

A triple offset valve operates with a quarter turn (90 degrees) and accepts any quarter-turn operator, whether pneumatic, hydraulic or electric actuator or a manual gearbox.

1.      First offset: The shaft is moved behind the sealing line so that the sealing surface forms an uninterrupted ring.

2.      Second offset: The shaft is moved sideways from the pipe and valve centerline, so the sealing surface lifts away from the seat quickly as the disk opens.

3.      Third offset: Seat and seal ring are machined with a conical geometry whose axis is inclined to the pipe axis; this angle enables friction-free rotation.

4.      Torque seating: At the last moment of closing the seal ring contacts the seat and is pressed by actuator torque; metal-to-metal sealing is achieved in both directions.

Friction-free rotation and torque seating

The absence of friction between seat and seal ring during rotation reduces wear and variation in operating torque. Braided graphite bearing protectors keep dirt out of the bearings, helping to keep operating torque constant and the valve operable.

Isolation and process control

A robust seat integral to the body and optimized seating angles allow the valve to be used for both isolation and process control. The maximum allowable pressure differential depends on trim selection: five trim levels are available from 10 bar to 160 bar at ambient temperature.

Key Features

·         All-metal, fire-resistant construction: An elastomer-free sealing system verified by fire testing.

·         Hardfaced body seat: Grade 21 cobalt-based hardfacing on the seat integral to the body.

·         Replaceable laminated ring: Multi-layer duplex and graphite seal ring that can be replaced without special tools.

·         One-piece shaft: A single-piece shaft transfers torque efficiently, with a keyed shaft-to-disc connection.

·         Low-emission packing: Graphite packing held by a split, two-part gland; construction verified by fugitive emission tests.

·         Heavy-duty bearings: Bearings designed for heavy pressure loading and wear resistance, shielded by braided graphite protectors.

·         Shaft blowout protection: Design against internal and external shaft ejection in line with international standards.

·         Easy installation: Open/closed disc references and an external disc position indicator; spot-faced flange bolting areas.

Technical Specifications

The table summarizes key configuration data of the triple offset butterfly valve series.

Dimension and weight tables are a selection; a wider configuration range is evaluated per project.

Key Advantages

·         Zero visible leakage: Reliable isolation with bidirectional, metal-to-metal sealing.

·         Long life: Friction-free rotation and a hardfaced seat keep wear to a minimum.

·         Fire safety: All-metal construction and fire test verification.

·         Economy at large sizes: A compact, light isolation solution up to a nominal size of 3450 mm (DN 80–3450).

·         Versatility: Combines isolation and process control in one valve and is compatible with a very wide range of fluids.

Applications

Triple offset butterfly valves are used with a very wide range of fluids and sectors: crude oil, jet fuel, gasoline, sour and acid gas, syngas, natural gas, flare gas, carbon dioxide, hydrogen, oxygen, acids, ammonia, chlorine, steam, heat transfer fluids, flue gas, potable water, seawater and wastewater are some examples.

Oil, gas and petrochemicals

Isolation and control on lines carrying crude oil, natural gas, sour gas and petrochemical intermediates.

Power generation and district heating

Steam and hot water lines in fossil-fired, geothermal, solar and hydroelectric plants and in district heating systems.

Water, desalination and wastewater

Large-bore isolation in potable water, seawater, desalination and wastewater facilities.

Mining, marine and other sectors

Applications in coal, mining, shipbuilding, food and beverage and aerospace.

Triple Offset Valve Selection Criteria

Selecting a triple offset valve requires pressure differential, material and body type to be evaluated together.

Pressure differential and trim

·         Trim level (A–E) according to maximum shutoff pressure differential

·         Design pressure and ASME / PN class

·         Whether isolation, process control or both are required

Material and fluid

·         Corrosive and abrasive character of the fluid

·         Design temperature and low-temperature requirement

·         Sour service and H2S partial pressure

·         Seal ring type (laminated or solid)

Body type and actuation

·         Double-flanged, lug, wafer or buttweld body

·         Face-to-face standard (ISO 5752, EN 558, API 609)

·         Actuator type, fail position and operating torque

·         Fire safety, emission and SIL requirements

Standards and Certifications

The triple offset butterfly valve series is manufactured within the following design, test and certification framework.

Regional product certificates (e.g. Eurasian Customs Union technical regulations, Canadian registration number) are listed in the manufacturer's certification table and must be confirmed according to project requirements.

TLY Enerji Isolation Engineering

Triple offset valves are frequently selected for critical isolation points that combine high temperature, fire safety and zero leakage expectations. If trim level, material and actuator torque are not chosen correctly at these points, sealing performance does not reach the expected level. TLY Enerji handles selection by considering these parameters together.

Trim and material are defined from shutoff pressure differential, temperature, fluid and body type, and fire safety, emission and SIL requirements are checked against the project specification. Actuator sizing and mounting orientation recommendations are included in the quotation, and certificate and test documentation is compiled according to project requirements. Commissioning and site support are coordinated according to the project plan, and seal ring and packing replacement steps are added to the documentation for maintenance teams.

·         Trim and material selection

·         Specification compliance check

·         Actuator sizing

·         Certificate and test documentation

·         Commissioning coordination

Frequently Asked Questions

What is a triple offset valve?

A triple offset valve is an all-metal butterfly valve with a conical sealing geometry in addition to two offsets in the shaft and disk axes. This geometry keeps the disk from rubbing the seat during rotation, and the disk seats only at the last moment of closing. Sealing is achieved by metal-to-metal contact and actuator torque.

Does a triple offset valve really give zero leakage?

This valve series seals in both directions without visible leakage in tests carried out first with water at high pressure and then with air at low pressure. This performance is verified against the Leakage Rate A criterion of ISO 5208 and EN 12266-1 and against the requirement defined by API 598 for resilient seated valves.

What is the difference between a triple offset and a double offset valve?

In double offset valves the disk may rub the seal briefly in the last part of its travel, and soft seals are commonly used. In triple offset valves the added conical geometry eliminates rubbing completely and makes metal-to-metal seating possible, which is an advantage in services requiring high temperature and fire safety.

Which pressure differentials can it handle?

The maximum allowable pressure differential depends on the trim level. At ambient temperature it is 10 bar for trim A, 25 bar for trim B, 52 bar for trim C, 110 bar for trim D and 160 bar for trim E. Body pressure classes range from ASME Class 150–1500 and PN 10–250.

Are triple offset valves fire resistant?

The all-metal construction, with no elastomers in the sealing system, helps maintain sealing under fire conditions. The series is verified to the API 607 fire test standard. If a different fire test standard is required in the project specification, it must be confirmed separately.

Can triple offset valves be used for control?

Yes. A robust seat integral to the body and optimized seating angles allow the valve to be used for both isolation and process control. For control duty, actuator, positioner and trim should be selected according to process data.