Butterfly valves make flow control easier and more efficient across all industries. They are quarter-turn rotary valves with a disk that rotates within the pipe, occupying little space while providing superior performance. Butterfly valves are easier to install, require less maintenance, and save a significant amount of money than their more complicated relatives. The fundamentals, types, uses, advantages, disadvantages, and principles of operation of butterfly valves are clarified in this guide.
What is a Butterfly Valve
A butterfly valve controls the flow of liquids or gases using a round disk on a rod that turns 90 degrees to open or close. This disk will permit full flow or fully shut off the flow, with any positioning in between for throttling functions. The valve body holds the disk and stem, and the seal is made using seats or liners
When completely opened, the disk is parallel to the flow, providing very little resistance; when closed, it turns perpendicular to the pipe centerline, seating on the seat to restrict flow. Butterfly valves are available in a range of pressure ratings and body types, such as wafer, lug, and flanged designs. The small face-to-face size and light weight make butterfly valves especially appealing for space-constrained applications.
Types of Butterfly Valve
Zero-offset Butterfly Valve
Zero-offset butterfly valves are the most basic and widely used. In this design, the stem is placed right in the middle of the disk, so the disk touches the seat evenly all around. The disk has a single axis of rotation that is carefully aligned with the pipe and valve seat centre.
When shut off, the edge of the disk bears against a flexible elastomeric seat and forms a bubble-tight seal appropriate for lower-pressure processes. These valves are cost-effective and simple, excellent for general service in water, air, and gas plants at moderate temperatures and pressures. Their durable seats possess superior seal characteristics and are resistant to particulate matter.
High-Performance Double Offset Butterfly Valve
Double offset butterfly valves possess two minor shifts in the position of the stem and disk. These design modifications assist the valve to work more efficiently at higher pressure and temperature compared to the standard zero-offset type.
- The first offset moves the stem behind the centre of the disk, reducing friction during opening and closing.
- The second offset shifts the stem sideways toward the centre of the pipe, allowing the disk to move away from the seat more smoothly.
These misalignments made intentionally in design produce cam-like action upon operation, minimize seat wear by reducing friction when opening and closing, and permit the disk to withdraw fully from the seat up to the last closing angles.
This design enhances throttling capabilities and enables the valve to handle elevated pressures and temperatures more effectively than its concentric counterpart. Double offset valves normally employ reinforced PTFE, metal, or special polymer seats that are more durable under difficult conditions.
Triple Offset Butterfly Valve
Triple offset butterfly valves take this a step further by adding a third shift in design, which gives an even tighter seal and better performance—especially in tough conditions. In addition to the two offsets used in double offset designs, triple offset valves have a conical seat design in which the seating surfaces slope about the pipe centerline.
This geometry provides a helical motion when the valve is operating, eliminating sliding contact between the disk and seat until the point of closure. The resulting metal-to-metal or metal-to-laminated seal provides absolute zero-leakage performance even at harsh temperatures and pressures.
Triple offset valves are best in severe service applications where unfaltering absolute shut-off is a necessity, e.g., in steam systems, hydrocarbon processing, and emergency shutdowns.
Application of Butterfly valve
Butterfly valves play pivotal roles in various industries because of their versatility and functionality. They manage flow in filtration equipment, chemical dosing units, and large distribution pipes in water treatment plants. They are applied in the oil and gas industry for isolating pipelines, segregating products, and tank farms.
HVAC systems apply butterfly valves to control flows of chilled water, condenser water, and steam to make commercial building temperatures exact. Sanitary butterfly valves are employed by food and beverage processing facilities in production lines where sanitation is of the utmost importance.
They find use in marine applications with their compact nature and corrosion-resistant versions for ballast systems. They are used for emissions control equipment and cooling water systems in power plants. Mining facilities prefer their reliability for slurry processing and water management.
Pros of a Butterfly Valve
- Offer a space-efficient design that requires minimal installation footprint.
- Fit well in congested piping systems due to compact size.
- It has lightweight construction that reduces structural support needs and allows easier handling.
- They operate with a quarter-turn, allowing quick opening and closing during emergencies.
- It provides good throttling characteristics for accurate flow control between open and closed positions.
- When fully open, there is very little pressure drop in it, which increases system effectiveness and lowering pumping expenses.
- Make use of a straightforward design with few moving parts to guarantee high dependability and minimal upkeep.
- It stays cost-effective, especially in larger sizes, offering significant economic benefits.
Cons of a Butterfly Valve
- Keep the disk in the flow path even when fully open, causing permanent pressure drop and turbulence.
- Experience disk flutter and increased wear in high-velocity systems if kept partially open.
- Provide less accurate throttling control than specialized control valves at low flow rates.
- Depend on elastomeric or polymer seats that deteriorate under extreme temperatures or chemical exposure.
- Require high operating torque in larger sizes, needing gear operators or actuators, which add complexity and cost.
- Have a thin disk profile that becomes vulnerable to water hammer effects in liquid systems.
- Suffer from premature seat wear and leakage when handling particulate-laden media.
Working Principle of Butterfly Valve
In simple terms, butterfly valves work by spinning a flat disc on a fixed shaft to control how much fluid passes through the pipe. The disk is supported on a stem that passes through the valve body to an external actuator, which can be a hand wheel, gear operator, or motor. In the completely open position, the disk sits parallel to the direction of flow, permitting media to pass unobstructed.
As the stem is turned by the actuator, the disk slowly rotates into the perpendicular position, limiting flow. At 90 degrees from completely open, the disk reaches full closure by clapping against the valve seat.
The seal mechanism differs depending on the design—resilient-seated valves employ compression of elastomeric seats, whereas high-performance types depend on close-machined metal or composite seating surfaces. Torque demand tends to be highest at about 70-80 degrees open, where flow forces bear heavily on the disk.
Conclusion
Butterfly valves illustrate how straightforward engineering principles lead to highly efficient flow control systems. Their quarter-turn operation, compact size, and multiple performance capabilities make them an essential component in myriad systems. For your next project requiring fluid handling, call upon Brick & Bolt’s engineers to identify the best valve option for your application.
Apoorva H P Achar