Introduction
Butterfly valves are an essential part of any fluid or gas handling system and are used to control the flow of material through pipes. They are classified into three types based on their design, construction, and applications. In this article, we will discuss in detail the three types of butterfly valves, their characteristics, advantages, and disadvantages.
Type 1: Concentric Butterfly Valve
The concentric butterfly valve, also known as the wafer butterfly valve, is the most common type of butterfly valve. It is designed in such a way that the disc is centrally positioned in the valve body, with the stem passing through the disc to connect it to the actuator.
Design and construction
The concentric butterfly valve has a circular disc that rotates around a central axis. The disc can be moved either perpendicular or parallel to the flow of the fluid or gas through the pipeline. The valve seat is placed on the inner surface of the valve body, where it makes contact with the disc to seal the connection.
The valve seat is lined with a soft material such as rubber or Teflon to prevent leakage and provide a good seal. The valve is held in position by two flanges on either side of the valve body. The stem is attached to the disc and protrudes out of the valve body to connect to the actuator.
Applications
Concentric butterfly valves are used in a range of applications, including water treatment plants, oil and gas pipelines, power plants, and HVAC systems. They are used to isolate or regulate the flow of fluids or gases in piping systems.
Advantages
- Lightweight and compact design
- Easy to install and maintain
- Low cost
- High flow capacity
- Low pressure drop
Disadvantages
- Limited temperature and pressure capabilities
- Prone to wear and tear
- Can be affected by pipe vibrations and turbulence
- Not suitable for abrasive or corrosive materials
Type 2: Double Offset Butterfly Valve
Double offset butterfly valves have an offset disc design, which means that the disc is not positioned in the center of the valve body, but rather offset from the center by a certain degree. The offset disc design allows for a greater range of movement and allows for complete seal of the valve.
Design and construction
The double offset butterfly valve has a spherical disc and a spherical valve seat. The seat cone angle is very small, allowing for the disc to seal against the valve seat. The stem connects to the disc and passes through the valve body to connect to the actuator.
Double offset butterfly valves are available either with or without a flange. Flanged valves have two or more flanges that bolt together. Non-flanged valves are suitable for use with grooved piping systems, which require less maintenance.
Applications
Double offset butterfly valves are used in a range of applications, including chemical plants, offshore and onshore oil rigs, petrochemical plants, and power plants. They are suited for applications that require tight shut-off and high performance.
Advantages
- Provides tight shut-off
- Resistant to wear and tear
- Suitable for high temperatures and pressures
- Low operating torque
Disadvantages
- Relatively expensive
- Cannot be serviced in-line
- Can experience disc flutter at low flow rates
Type 3: Triple Offset Butterfly Valve
Triple offset butterfly valves have an offset disc design, similar to that of double offset butterfly valves, but with an additional offset in the form of a conical axis. This helps to provide better sealing and less operating torque than double offset butterfly valves.
Design and construction
The triple offset butterfly valve has a conical disc and a corresponding valve seat. The angle and shape of the disc and the valve seat are designed to create a metal-to-metal seal. The stem connects to the disc and passes through the valve body to the actuator.
Triple offset butterfly valves are available with both flanged and non-flanged ends. Flanged valves are typically used in oil and gas production, petrochemical plants, and other high-pressure applications, while non-flanged valves are used in water treatment and HVAC systems.
Applications
Triple offset butterfly valves are used in a variety of industrial applications, including oil and gas production, chemical plants, power plants, and HVAC systems. They are suited for applications that require a tight shut-off, high performance, and low maintenance.
Advantages
- Excellent sealing performance
- Low operating torque
- Suitable for high temperatures and pressures
- Suitable for abrasive and corrosive materials
Disadvantages
- Expensive
- Requires periodic maintenance
- Can experience disk flutter at low flow rates
- Requires accurate alignment during installation
Conclusion
Butterfly valves are an essential part of any fluid or gas handling system and can be classified into three main types based on their design and construction. Concentric butterfly valves are the most common type and are used in a range of applications, while double offset and triple offset butterfly valves are used in more demanding applications that require tight shut-off and high performance. Choosing the right type of butterfly valve is crucial to ensure optimal performance, efficiency, and reliability of your system.
