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Triple eccentric butterfly valves, also called triple offset butterfly valves, are critical in applications where bubble-tight shut off is required. In some applications, bubble-tight shut off cannot be achieved using double eccentric butterfly valves. Some applications don't lend themselves well to traditional butterfly valves, e.g., applications involving harsh chemicals or media containing small particles that tend to clog valves and pipelines. In such applications, triple eccentric butterfly valve shows outstanding advantages.

Triple Offset Technology

A triple offset butterfly valve has 3 separate offsets. Two of the offsets apply to the position of the shaft in respect to the centerline of the bore and the centerline of the disc/seat sealing surfaces. The third offset is the design in the axis of the seat cone angle.
 
Zero offset: Disc rotates around the centre axis allowing for a potential 360º rotation. Sealing is achieved by the disc deforming the soft seal, thus generating full friction throughout the 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). This creates a cam action during operation to lift the seat out of the seal resulting 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. This ensures that there is a friction-free stroke through its full operating cycle. Contact is only made at the last point of closure with the 90 degree angle acting as a mechanical stop so that the disc seat cannot move excessively.



The Advantages of Triple Offset Technology

• The "cam action" and "right angled" conical sealing design ensures that the metal sealing elements will not be in contact until its final degree of closing, thus achieving repeatable sealing and greatly prolonging the service life of the valve.
• Metal-to-metal sealing ensures bubble tight shut-off, resulting in zero-leakage. 
• Suitability to the harsh medium – structure of the valve features no elastomers or materials usually affected by corrosion.
• The geometric design of the sealing element provides a friction-free stroke for the the valve. This extends valve life and allows installation of lower torque actuators.
• There is no cavity between the sealing parts, hence no blockage, low maintenance, and prolonged valve life.