Emerson Exchange 365

Valves for Frequent Cycling, High Pressures and Temperatures

Emerson's David LeavittDavid Leavitt described an application of high-cycling valves in a dehydration process at the Offshore Technology Conference (OTC) in Houston, Texas. I recapped his presentation last week in a post, Triple Offset Valves and Molecular Sieve Adsorption Applications.

He compared rising stem ball valves and triple offset valves (TOVs) used in these applications. David describe a concentric butterfly valve design, a dual offset with a triple offset design. In this post, I share more about the differences in valve types for this application and why triple-offset valves are a strong candidate for high open/close and temperature cycling applications such as molecular sieves.

Triple-offset valves, as quarter turn valves, are metal-to-metal torque seated with cone in cone seating. The three offsets are:

Offset 1
The shaft is placed behind the plane of the sealing surface to provide a continuous seat path.

Offset 2
The shaft is placed to one side of the pipe/valve centerline to allow the displacement of the seal from the seat during the 90° opening.

Offset 3
The seat and seal cone centerlines are inclined in respect to the pipe/valve centerline. This third offset completely eliminates rubbing.

The Vanessa TOV trim design, seating angles and surface finish all contribute to a very low, consistent and predictable torque demand which is unaffected by fluid temperatures and pressures throughout the valve life.

The metal seal ring has elastic properties which allow for radial compression to be uniformly distributed around the seating surface. These are key contributors to the zero-leakage performance of the valve.

The lack of contact between sealing elements when opening and closing, combined with low and consistent torque levels across the quarter-turn of operation make this valve technology for emergency shutdown, blow off or frequent cycling, such as molecular sieve applications.

Learn more about Vanessa Triple Offset Valve technology in the Triple Offset Valve area of Emerson.com, and if you’re here with us in Houston for OTC, visit with the valve experts in Emerson booth #2261 in the OTC exhibit area.

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