High-performance butterfly valves are a common solution for equipment isolation and other on/off applications across a wide range of chemical and petrochemical processes. My article in the November 2024 issue of Valve World, titled “Choosing butterfly valves for complete shutoff,” discusses key design features of these valves to help users evaluate the best alternatives for their applications.
Common applications
While a high-performance butterfly valve may be used in a variety of situations, they are best suited for equipment isolation and on/off applications requiring bubble-tight, zero-leakage shutoff.
These valves are generally less expensive and take far less space than plug or ball valves. There are a multitude of butterfly valve designs on the market, varying significantly in sealing performance and long-term reliability.
Sealing and packing designs
When evaluating a high-performance butterfly valve, users should start with the disc and seat design. Some butterfly valves wedge the disc into a soft seat and rely on process pressure to provide reliable shutoff. Such valve designs only work with pressure on a particular side of the valve and will perform poorly in bi-directional applications. Other valves utilize seat designs that continuously wear as the valve moves, creating leakage after a short time in service, and eventually causing premature failure of the seat.
Better designs feature a double offset that lifts the disc off the seat within a few degrees of travel, while still allowing the disc to wedge tightly into the seat when closed, regardless of system pressure. These designs retain bubble-tight sealing, while decreasing wear for extended service life. Designs incorporating a self-adjusting seal made with long-lasting materials extend valve life even further.
Long life high-performance valves, like Emerson’s Keystone™ K-LOK® Series 38, utilize a double offset design paired with a heavy-duty polymer seat, backing rings, and internal wire wraps to allow the seal to adjust as the disc cams into it
Current environmental standards require minimal emissions, which typically requires high-compression packing. Live-loaded packing washers and advanced sealing ring materials provide adjustable compression to keep emissions low, while maintaining ease of stem movement and reducing component wear.
Body design considerations
For ease of installation and maintenance, user-friendly valves should feature standard face-to-face dimensions, an extended stem to accommodate insulation, and a mounting base that accepts most actuators without requiring coupling or additional brackets. Some valve designs also feature a reduced-profile stem/disc to maximize flow capacity.
A high-performance butterfly valve body should include standard take-out dimensions, allow direct actuator mounting, and maximize valve capacity when fully open
Ease of maintenance
While a top-tier high-performance butterfly valve will last for years, eventual seat and packing wear are inevitable, so these components should be easy to repair or replace without disassembling the valve stem and disc. Though such repairs should be infrequent, ease of maintenance further reduces lifecycle costs.
High performance valves should be designed with maintenance in mind to allow typical repairs, such as a seat or packing replacement, without valve disc or stem disassembly.
Key advantages
High-performance butterfly valves offer superior sealing for equipment isolation and other on/off applications, and at a low cost and with a small form factor as compared to other valve body styles. Features such as double offset sealing, advanced disc seat designs, and low emission packing improve performance significantly, providing additional lifecycle cost savings.
Visit the Keystone Butterfly Valves section on Emerson.com to know the complete range of butterfly valves from general purpose through to heavy duty and high performance models
