A butterfly valve is a flow control device with a rotating disc that regulates fluid passage.
Principle of operation
Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they cost less than other valve designs, and are lighter weight so they need less support. The disc is positioned in the center of the pipe. A rod passes through the disc to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow, so it induces a pressure drop, even when open.
A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. The “butterfly” is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid. The valve may also be opened incrementally to throttle flow.
There are different kinds of butterfly valves, each adapted for different pressures and different usage. The zero-offset butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high-performance double offset butterfly valve, used in slightly higher-pressure systems, is offset from the center line of the disc seat and body seal (offset one), and the center line of the bore (offset two). This creates a cam action during operation to lift the seat out of the seal resulting in less friction than is created in the zero offset design and decreases its tendency to wear. The valve best suited for high-pressure systems is the triple offset butterfly valve. In this valve, the disc seat contact axis is offset, which acts to virtually eliminate sliding contact between disc and seat. In the case of triple offset valves the seat is made of metal so that it can be machined such as to achieve a bubble-tight shut-off when in contact with the disc.
Types
- Concentric butterfly valves – this type of valve has a resilient rubber seat with a metal disc.
- Doubly-eccentric butterfly valves (high-performance butterfly valves or double-offset butterfly valves) – different type of materials is used for seat and disc.
- Triply-eccentric butterfly valves (triple-offset butterfly valves) – the seats are either laminated or solid metal seat design.
- Butterfly valve with actuator electric valve – An electrically actuated butterfly valve is a quarter-turn valve controlled by an electric motor. It offers fast and precise flow regulation, remote operation, and versatility for various applications.
What is a butterfly valve used for?
Butterfly valves for water are used as control valves in pipelines to shut off water flow. These valves are available in huge sizes and are suitable for handling slurries and liquids with relatively large amounts of solids at low pressures.
What are the main parts of a butterfly valve?
The components of butterfly valves are made up of four main parts: the body, disk, stem, and the seat.
How to open/close a butterfly valve?
That is to say, turning the handwheel anticlockwise is to open the valve. And turning the handwheel clockwise is to close the valve. No matter electric butterfly valve or pneumatic butterfly valve, the manual function is generally consider in the valve design. Which is generally realized by hand wheel or handle.
What is the main advantage of a butterfly valve?
The disc is lighter than a ball, and the valve requires less structural support than a ball valve of comparable diameter. Butterfly valves are very precise, which makes them advantageous in industrial applications. They are quite reliable and require very little maintenance.
