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OFFSET BUTTERFLY VALVES

TRIPLE OFFSET BUTTERFLY VALVES (TOV)

OVERVIEW

Compared to traditional valves, butterfly valves are smaller and lighter, making them ideal for space-conscious plant designs. However, conventional, high-performance or interference fit butterfly valves do not have the control or shut off requirements for high pressure, high-temperature applications. The Triple Offset design moves the center of rotation within the valve. It utilizes an ellipsoidal sealing geometry, allowing a wide range of metal seating materials to be used, providing zero-leakage performance on high temperatures, high pressure, and fire-safe applications.

Compared to the double eccentric butterfly valve design, which is position seated and requires high friction to seal (this will accelerate seal wear due to friction), triple offset butterfly valves are torque seated. Excess rotation of the valve causes more significant interference between the disc and the seat due to the eccentric geometry. With the proper torque, they will meet bi-directional zero leakage shutoff per API 598.

SEATING ARRANGEMENTS IN TOV

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Laminated Disc & Integral Body Seat

It is essential to understand the seating arrangement when selecting a TOV design. Since the early 1960s, when the triple offset was first patented, there have been several design iterations. The original and most common design utilizes and laminates seat on the disc edge, and an integral body seat. The alloy and graphite lamination gives the seat the memory required to provide repeatable zero-leakage isolation. Due to the graphite being the most vulnerable seat component, it should ideally not reside directly in the flow path for application where solids may be present.

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Solid Disc & Replaceable Laminated Body Seat

In the early 2000s, a new configuration of the TOV was patented. This design employed a solid stainless-steel disc with the laminated seat in the body. This design removes the laminated sealing component from the flow path and relocates it in the body protecting the graphite. This design can also handle up to 10% entrained solids with the addition of hard-facing overlays. The primary downfall of this design is its difficulty in its service. Any wear on the disc edge leads to primary component replacement, which can become costly on larger sizes.

This reiteration of the TOV encompasses previous designs’ strengths related to performance, reliability, and repairability. A replaceable solid metal seat on the disc edge and replaceable laminated seat in the body allows for a true severe service Zero Leakage Triple Offset valve.

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FEATURES

Triple Offset Butterfly valve features:

      • Robust design and construction
      • Friction-free metal seats
      • Bidirectional sealing
      • Zero leakage
      • Inherently fire safe

APPLICATIONS

Triple Offset Butterfly valves are used in many severe service applications, such as: 

      • Oil & Gas/Refining
      • Chemical & Petrochemical Processing
      • Power
      • LNG & Cryogenics

FIVE OFFSET BUTTERFLY VALVES

The butterfly valves' development has continued to evolve, and N2X is happy to introduce the only 5-offset butterfly valve in the world: KU V-AXX® 5-offset butterfly valve.

DESIGN

The additional offsets comprise of the following: 

      • Re-shaped seat cone changes the seating area from an elliptical to a circular shape, which will increase the Cv value of the valve
      • The sharper angle of the seat on the shaft area eliminates the 10% rubbing that was still happening in Triple Offset Butterfly valves (in the 6 and 12 o’clock positions), resulting in 0% rubbing or friction, lower torque, and faster opening and closing
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Seat Geometry

In the newly designed KU V-AXX® Five Offset butterfly valve, the seat shape can be changed around the whole seat without restrictions. If necessary, the seat’s angle, even in the shaft area, can be 25° or more, without changing the angle in other areas. This is only possible due to the unique seat design, which is not formed by a simple cone but by a much more complex figure, not yet named in geometry.

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Cv Values

The KU V-AXX® 5-Offset butterfly valve has the highest Cv value of any comparable torque seated butterfly valve. Re-shaping the seat cone that changes the seating area from elliptical shape to circular increases the Cv value of the valve by 18-20% compared to Triple offset butterfly valves.

Having a higher Cv allows for smaller valve size options. The smaller valve has a lower torque value, which requires a smaller actuator. Therefore, a valve with a higher Cv value could potentially reduce the cost of the assembly significantly.

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APPLICATIONS

The KU V-AXX® Five Offset design is suitable for extremely high or low-temperature applications or applications where the body and internals have different temperatures. We still need to achieve a tight shutoff with a metal seated configuration. This design has been used successfully in applications from -270°C up to 1800°C.

FEATURES

      • New seat design; no friction or wear (0% rubbing)
      • Suitable for erosive or slurry applications; the 0% rubbing minimizes the wear and erosion of the disc seal
      • Full pressure-tight bi-directionally
      • Suitable for applications from -270°C up to 1800°C
      • Different disc seal design and materials available for various applications
      • Body seat is solid metal and is in Inconel as standard
      • Higher Cv value comparing to all torque seated valves in the market

OFFSET BUTTERFLY VALVE SUMMARY

All of these Butterfly valves have their distinct advantages. There are many available options; therefore, we utilize our valve expertise to analyze the technical and commercial requirements and then select and propose the best combination of technology and commercial value for any given application. Please contact the N2X Application Engineering Team for more details.