Application of Triple Offset Butterfly Valves

What is Triple Offset Butterfly Valve?

A triple-offset butterfly valve has three separate offsets. Two of these apply to the location of the shaft with respect to the center line of the bore and the center 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 center 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 center line of the disc seat and body seal (offset one), and the center 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 the 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 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.
The 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.

Application of Triple Offset Butterfly Valves

At present, a butterfly valve, as a component used to realize the on-off and flow control of pipeline systems, has been widely used in the petroleum, the chemical industry, metallurgy, hydropower, and other fields. In the butterfly valve technology known to the public, its sealing form is mostly used in the sealing structure, in sealing material like rubber, polytetrafluoroethylene, etc. Due to the limitation of structural characteristics, it is not suitable for high temperature, high pressure, corrosion resistance, wear resistance, and other industries. An existing more advanced butterfly valve is a three-eccentric metal hard seal butterfly valve, with the valve body and valve seat as the connecting members, valve seat sealing surface welded with high temperature and corrosion resistant alloy materials. The multi-layer soft stacked sealing ring is fixed on the valve plate. Compared with the traditional butterfly valve, this kind of butterfly valve has high-temperature resistance and is easy to operate, without friction when opening and closing. Moreover, the butterfly valve is automatically closed when the torque of the transmission mechanism increases to compensate for the sealing, which improves the sealing performance and extends the service life of the butterfly valve. However, there are still the following problems with the use of this butterfly valve:

1. As the multi-layer soft-hard overlapping sealing ring is fixed on the valve plate when the valve plate is normally open, the medium forms a frontal scour on its sealing surface, and the soft sealing belt in the interlayer of the metal sheet is scoured, which directly affects the sealing performance.
2. Restricted by the structural conditions, this structure is not suitable for valves with a diameter less than DN200, because the overall structure of the valve plate is too thick and the flow resistance is high.
3. Because of the principle of a three-eccentric structure, the sealing surface of the valve plate and the seat between the seal is driven by the torque of the valve plate pressure to the seat. In the positive flow state, the higher the medium pressure is, the tighter the sealing extrusion will be. When the medium is flowing upward, the pressure of the medium increases, along with which the positive pressure value between the disc and the seat is lower than the pressure of the media, and the seal begins to leak.

The high-performance three-eccentric bidirectional hard sealing butterfly valve is characterized in that the seat sealing ring is composed of two layers of stainless steel plates on both sides of the soft t-shaped sealing ring. The sealing surface of the valve plate and the valve seat is an inclined conical structure, and the high temperature and corrosion-resistant alloy material are surfacing welded on the inclined conical surface of the valve plate. The spring fixed between the adjusting ring pressure plate and the adjusting bolt assembly on the pressure plate is arranged together. This structure effectively compensates the tolerance belt between the shaft sleeve and the valve body and the elastic deformation of the valve stem under the pressure of the medium and solves the sealing problem of the valve in the process of two-way interchangeable medium transportation.

The use of soft t-type two sides of the multi-layer stainless steel sheet seal ring has the double advantages of hard metal seal and soft seal and, regardless of low temperature and high temperature, has zero leakage sealing performance.

The test proves that when the pool is in a positive flow state (the flow direction of the medium is the same as the rotation direction of the butterfly valve plate), the pressure on the sealing surface is generated by the torque of the transmission device and the action of the medium pressure on the valve plate. When the positive medium pressure increases, the tighter the extrusion between the valve plate’s oblique conical surface and seat sealing surface is, the better the sealing effect is.

When in reverse flow, the seal between the disc and the seat forces the disc against the seat by the torque of the drive device. With the increase of the reverse medium pressure, the unit positive pressure between the valve plate and the seat is less than the medium pressure, and the adjustment ring spring in the load after the storage of the deformation can compensate for sealing, the tight pressure of the valve plate and seat sealing surface plays an automatic compensation role. Therefore, the utility model is not like the existing technology, which installs the soft and hard multi-layer sealing ring on the valve plate, but directly installs it on the valve body, and adding the adjusting ring between the pressure plate and the seat is a very ideal two-way hard sealing way. It will replace gate valves and globe valves.