Butterfly valves are versatile throttling and shutoff valves used to control flow in a wide range of industrial piping systems. Typically actuated by manual gear, lever, or handwheel mechanisms, butterfly valves can also be automated with actuators that allow remote control. Electric and pneumatic actuators coupled to butterfly valves create smart, powered valves capable of precision flow control.
Electric actuators provide fast, precise valve positioning in response to electronic control signals. Pneumatic actuators deliver robust valve opening and closure using pressurized air as the power medium. Combining electric and pneumatic actuation creates hybrid valves with enhanced capabilities.
An electric pneumatic butterfly valve uses an electric actuator for accurate positioning control paired with a pneumatic actuator for fail-safe emergency shutdown. This hybrid approach harnesses the strengths of both technologies.
In normal operation, an electric motor or electric linear actuator with position feedback provides precise valve control in response to 4-20mA or network control signals. Fast response times, positioning accuracy, and PID functionality enable tight flow control.
For emergency shutdown, a pneumatic spring return actuator is mounted in parallel. This actuator remains pressurized during normal operation to hold the valve open. In an emergency, cutting off air pressure causes the spring return to snap the valve shut quickly and decisively.
Key Benefits Of Butterfly Valves:
• Precision flow control via electric actuation
• Fast emergency shutdown via pneumatic actuator
• Independent shutdown mechanism for safety
• Lower air consumption than fully pneumatic valve
• Position feedback for operational monitoring
• Capable of both throttle control and tight shutoff
The electric control circuit can sense if air pressure is lost and trigger a controlled shutdown sequence before the pneumatic actuator closes the valve. This prevents abrupt valve slam. Position transmitters track valve position continuously.
These hybrid valves are used for critical piping and transfer systems handling volatile or hazardous media. By combining electric and pneumatic functionality, they satisfy both precision control and emergency shutdown requirements.
Pneumatic butterfly valves use pressurized air to pneumatically position the valve and provide fail-safe shutdown capabilities. They are intrinsically safe since the air supply can be exhausted for emergency shutdown.
Quarter-turn pneumatic actuators are commonly used. They provide rotary torque to open or close the butterfly disc through 90°. Linear pneumatic cylinders are also able to automate larger valves.
Pneumatic systems provide fast response for both valve positioning and shutdown. However, they lack the precision control and feedback available with electric automation. Positioners can be added to improve positioning accuracy.
Pneumatic actuators are also used for fail-in-place function where the valve maintains its position without air pressure. This avoids unsafe shutdowns, but loses emergency shutdown capability.
Butterfly valves typically use a centered circular disc as the throttling element. An offset disc that seals against an inclined seat can provide tighter shutoff. The triple offset disc design takes this further with multiple offsets to achieve zero seat contact in the open position.
The disc has two offset planes inclined relative to the shaft plane. When open, the disc tilts and lifts off the seat, eliminating rubbing and seat wear. The contoured seat provides tight shutoff when closed. Low torque requirements allow use of small, economical actuators.
Triple offset butterfly valves deliver precision throttling down to zero flow coupled with bubble-tight shutoff. This capability suits them for demanding control applications. Their compact wafer design permits easy automation while providing reliable performance.
Combining triple offset discs with electric and pneumatic actuation creates intelligent, powered butterfly valves. Electric control handles accurate flow modulation during normal operation. Pneumatic power provides emergency shutdown on demand. This dual functionality allows precision flow management along with fast, safe closure when required.
Electric pneumatic actuation, fail-safe shutdown mechanisms, and advanced disc designs enable butterfly valves to go beyond basic open/close duties. Precision flow control, tight shutoff, and intelligent functionality make them versatile automation candidates for critical industrial pipelines and processes.