BM Engineering explains triple offset butterfly valves

For any application requiring bubble-tight shut off, triple offset butterfly valves are arguably the perfect choice. PIF spoke to BM Engineering to find out more about the various advanced features and benefits that triple offset butterfly valves can offer users.

What are triple offset butterfly valves?

Before we go any further, let’s briefly cover what triple offset butterfly valves actually do. Essentially, they’re a type of butterfly valve featuring three offsets that work together to cut off media. Two offsets are placed to the side of the centre. The third is achieved via the geometry of the seating surface, creating a cone angle out of the disc and the seat. This feature, alongside the two eccentric shaft offsets, allows the disc to seal against the seat with no friction whatsoever.

The benefits of triple offset butterfly valves

If longevity is a factor in sealing applications, then you’ll be pleased to hear that triple offset butterfly valves boast a prolonged life-span. “The conical sealing design of triple offset butterfly valves ensures its metal sealing components are never in contact until its final degree of closing,” says Scott Miller of BM Engineering.

“This results in repeatable sealing and vastly extended valve life. The metal-to-metal sealing of triple offset butterfly valves is what causes its bubble-tight shut-off. A much-desired feature that results in zero leakage performance,” adds Scott.

“In addition, the geometric design of sealing components provides frictionless stroking throughout triple offset butterfly valves. This also contributes to its extended valve life and allows a lower torque actuator to be fitted, if required,” he adds.

Another benefit of the triple offset butterfly valve is its suitability in harsh media. “Materials such as elastomers, which are typically affected by corrosion, are not factored into the construction of triple offset butterfly valves,” explains Scott. “This explains why they work best with harsher media types”.

The technology behind triple offset butterfly valves

Triple offset butterfly valves harbour some sophisticated technology. “A triple offset butterfly valve has three working offsets: zero, double and the titular triple offset,” says Scott. “For the zero offset, the disc will rotate around the centre axis, allowing for a potential 360-degree rotation. Here, sealing is achieved by the disc deforming the soft seal, resulting in full friction throughout the operating cycle”.

Moving on to the double offset, in order for the seat to be displaced, the shaft of the valve must itself become offset. “This is achieved in two stages,” continues Scott. “First by becoming offset from the disc seat and body seal, before progressing to the centre line of the bore. These actions are offset one and two respectively. As a result, it creates a cam action that results in friction during the first 10 degrees of the opening and the final 10 degrees of the closing.”

The third and final offset is the geometry design of the sealing components. “These are each machined into an offset conical profile that forms a right-angled cone, ensuring frictionless stroking through its operating cycle. Contact will only be 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 and the titular triple offset of this butterfly valve,” Scott concludes.

For more information about triple offset butterfly valves, visit BM Engineering.

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