The working mechanism of a butterfly valve is quite simple and relatively similar to a ball valve. A butterfly valve is a quarter-turn rotational motion valve simply because a disc is mounted on a rotating shaft. In the open position, the disc is rotated one-quarter turn so that it is parallel to the flow. When the disc is closed, it is perpendicular to the flow and completely blocks the line. Valve movement is similar to that of a butterfly’s wing when it lands with its wings moving up and down in a 90-degree turn, that’s why it is called a Butterfly valve. A butterfly valve consists of four components: the body, the disk, the steam, and the seat.
Types of Butterfly Valve
Butterfly valves are a type of control valve that can be applied to different industries, including energy, petrochemical, and marine manufacturing. The valves are used to control the flow of fluids, gases, and slurries. Butterfly valves are designed in many different shapes, sizes, and configurations, but they all have the same general design. The valve consists of a disc with a rotating stem attached. The disc is usually connected to the stem, which is fitted into the pipeline through an end connection. The disc also has a seat that can be either eccentric or concentric.
The most common type of butterfly valve is a centric or concentric butterfly valve. In this type, the steam passes through the centerline of the disc, which is located at the center of the pipe bore, and the seat is the inside diameter of the valve body. This is also termed a zero-offset valve. For low-pressure ranges, butterfly valves are commonly used.
Eccentric Butterfly Valves
Eccentric butterfly valves have a stem that does not pass through the centerline of the disc, but rather behind it (opposite to flow direction). Single-offset valves have the stem located directly behind the centerline of the disc. It was designed to reduce disc contact with the seal before full valve closure in order to improve the valve’s service life. The single offset butterfly valve has now been replaced by double offset and triple offset butterfly valves.
Double offset Butterfly Valves
The stem of a double offset or double-eccentric butterfly valve is located behind the disc with an additional offset to one side. Double offset butterfly valves should always be set with the stem on the side opposite the disc center. The disc is the part of the valve that closes off the pipeline when the butterfly valve is turned. The stem is the part that moves with the disc, linking to the actuator. The double eccentricity of the stem allows the rotating disc to rub over the seat by only a few degrees.
Triple offset butterfly valves
Triple offset butterfly valves ( TOBVs ) are used in critical applications and are similar to double offset butterfly valves. The third offset determines the contact axis between the disc and the seat. As a result of the seating surface taking the shape of a conical cylinder, together with the ridge shape of the disc, there is little contact before the full closure of the valve. Triple offset butterfly valves are more efficient and require less maintenance than standard butterfly valves. In order to create a bubble-tight seal, triple offset valves have metal seats. With metal seats, butterfly valves are able to operate in higher temperatures.
Butterfly valve designs with high performance use the pipeline pressure to increase interference between the seat and the disc edge. They are more resistant to wear and have higher pressure ratings.
Advantages of butterfly valves
- Comparatively, the compact design requires significantly less space
- Light in weight
- Quick operation reduces opening and closing time
- Available in very large sizes
- Low-pressure drop and high-pressure recovery
Butterfly Valve vs Ball Valve
Butterfly valve :
- Lighter weight even at larger pipe diameters
- Requires smaller installation space
- It is cheaper than a ball valve, especially for larger sizes
- By restricting flow, the valve disc creates a pressure drop.
- Larger pipes (DN 150+) are particularly suited to this product due to their features
- This valve has a flange design with lugs or wafers.
- The larger the pipe diameter, the heavier it becomes, and support may be required
- A larger space is required compared to butterfly valves
- Costly compared to a butterfly valve
- There is no pressure drop with a full port ball valve.
- Suitable for smaller pipe diameters (below DN 50).
- Various connection types are available with threads and flanges.
Aira Euro Automation is the leading Butterfly Valve supplier in Oman. We supplied eccentric, double eccentric & triple offset butterfly valves in Oman. We also make valves as per customer requirements and drawings. All these types of butterfly valves are available in a huge range of sizes with manual handles, gear-operated, and pneumatic actuators. Not only in Oman, but we are the global supplier of industrial valves.