High-performance butterfly valves play a key role in equipment operation, isolation, and maintenance throughout the chemical and petrochemical industries. Crucial design features dramatically impact the performance and reliability of these valves, as discussed in my article from the February 2024 issue of Hydrocarbon Engineering, titled “High-Performance Butterfly Valve Selection.”
Butterfly valve advantages
Butterfly valves are well suited for many on/off applications. High-performance designs, in particular, offer bubble-tight sealing. They are also less expensive and more compact than ball or plug valves. The best designs provide long service life and low maintenance costs while consistently providing very tight shutoffs.
Bubble-tight seat design
Disc and seat design ultimately determine a valve’s shutoff performance. Tight shutoff typically comes with the tradeoff of increased wear, but advanced designs are capable of high performance over extended periods.
The valve disc can be made of a variety of materials, but it should always include some means of additional hardening in the sealing areas to minimize wear, and better designs will incorporate a double-offset alignment to ensure a tight seal.
The valve seat should be made of PTFE or RTFE and supported with a backing ring and internal wire wrap.
This combination creates a very strong seat which can move and adjust to the valve disc as it meets the seat, providing bubble tight shutoff, while wearing very slowly.
Long-life high-performance valves employ a heavy-duty polymer seat with backing rings, internal wire wraps, and carefully formed gaps so the seat can adjust to the valve disc as it cams into the seat. This combination provides a bubble-tight seal over an extended service life.
The snug interference fit between the seat and valve disc creates a leak-free seal under a wide range of pressure conditions on either side of the valve. To reduce wear, the disc completely disengages from the seat within seven degrees of valve travel.
Stem design for minimal leakage
Valve stem packing and sealing designs are also worth careful consideration, given today’s stringent regulations on fugitive emissions. Low leakage typically requires high packing compression, but smooth stem rotation conversely necessitates low friction.
Modern designs address this challenge by using live-loaded packing washers to maintain constant pressure on packing rings, which are made of varying materials according to the temperature and pressure requirements of the application. Such designs can maintain near-zero leakage for years of service.
Very low-emission packing is a crucial requirement of any high-performance valve in chemical or hydrocarbon applications. Near zero fugitive emissions over an extended service life are possible through the application of a variety of specialty materials and careful engineering.
Body design
In addition to valve seat and packing, key body design features should be considered, including:
- Standard face-to-face valve dimensions
- An elongated area between the packing adjustment area and valve body for insulation
- An ISO 5211 pad for direct actuator mounting
- A strong shaft with minimal surface area
- A lug body for dead-end service
High-performance valves incorporate design features to accept a wide range of actuators, maximize valve capacity, and provide bubble-tight sealing in bidirectional and dead-end service applications.
Ease of maintenance
Valve packing and seats inevitably wear out, but maintenance-friendly butterfly valves do not require the disassembly of the valve disc or stem for component service and replacement.
Certified performance
High-performance valves should meet a variety of applicable standards and certifications, including Directive 2014/68/EU of the European Parliament and of the Council, NAMUR NE 167, EN 593, EN 12569, ISO 15848-1 Tightness Class BH and Endurance Class C03, and EN 12266-1 Leakage Rate A.
Takeaway
High-performance butterfly valves are ideal for on/off chemical and petrochemical applications, offering an economical and compact alternative to other valve types. Improvements in seals and stem packing allow for tight shutoff and near-zero emissions over a prolonged service life. Consult with your valve vendor to find the best design for your application.
