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Why use a triple-offset butterfly valve?
Thu 18 Jan 2018

Why use a triple-offset butterfly valve?

For many applications requiring bubble-tight shut off, double offset butterfly valves simply do not make the grade. In these cases, Triple Offset Butterfly Valves are the perfect choice, as BM Engineering Supplies explains in this latest tutorial article.


What is a triple-offset butterfly valve?


A triple-offset butterfly valve has three separate offsets. Two of these apply to the location of the shaft in respect to the centre line of the bore and the centre line of the disc/seat sealing surfaces. While the third offset is the design in the axis of the seat cone angle.


Triple-offset Technology


Zero Offset: The Disc rotates around the centre axis, allowing for a potential 360 degree rotation. Sealing is achieved by the Disc deforming the soft seal. This results in full friction through the full operating cycle.


Double Offset: To allow displacement of the seat, the shaft is offset from the centre line of the disc seat and body seal (offset one), and the centre line of the bore (offset two). Thus creating a cam action during operation to lift the seat out of the seal. This results in friction during the first 10 degrees of opening and final 10 degrees of closing.


Triple Offset: The third offset is the geometry design of the sealing components. The sealing components are each machined into an offset conical profile resulting in a right-angled cone, which ensures friction-free stroking throughout its operating cycle. Contact is only made at the final point of closure with the 90 degree angle acting as a mechanical stop. This results in no over-travel of the disc seat.


The benefits of triple-offset valves


  • ‘Cam-action’ and ‘right angled’ conical sealing design ensures the metal sealing components are never in contact until its final degree of closing. This results in repeatable sealing and a vastly extended valve life.
  • Metal-to-Metal sealing ensures bubble tight shut-off, resulting in zero-leakage performance.
  • Suitability to harsh media because the construction of the valve features no elastomers or materials typically affected by corrosion.
  • Geometric design of sealing components provides friction-free stroking throughout the valve. This extends the valve life and allows a lower torque-actuator to be fitted.
  • There are no cavities between sealing components, resulting in no clogging, low maintenance and extended valve life.


Zwick triple-offset valves


Zwick valves are used for critical services in many global industries for liquids and gases. The triple offset valves are designed for temperatures up to 815°C and for cryogenic services. The triple offset geometry and the special features guarantee 100 per cent zero-leakage performance even during extreme temperature variation and pressure peaks.


TRI-CON valves offer the widest laminated seal ring in the market today, made possible by true cone-in-cone seating design which assures a frictionless opening and closing with lowest torques and without break-away torque. Zwick’s design provides 100 per cent tightness in gas services.

Among the special features are a self-centring disc construction that guarantees optimal position of the laminated seal against the seat and jamming due to thermal expansion is eliminated. The disc is keyed to the shaft rather than pinned. This provides balanced torque transmission and minimises the danger of pins shearing off.


The strong disc, with its elliptical supporting surface, also offers the best fixing of the lamination. Bubble tightness is achieved as a result of the special machining of the lamination. Plus, the optimal position of the bearing reduces the risk of the shaft bending. This guarantees bi-directional tightness at maximum differential pressure.


Speak to one of BME’s knowledgeable advisers about our full range of triple-offset butterfly valves today by calling 0141 762 0657 or email sales@bmengineering.co.uk. For more information please visit www.bmengineering.co.uk.test.

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