Definition and Comprehensive Guide to Flanged Butterfly Valve
A flanged Butterfly Valve refers to a type of valve with flanges at both ends of the valve body, connected to pipeline flanges via bolts. Its opening and closing are achieved by the rotation of the disc around the valve stem. It serves as a key on-off valve in pipelines due to its simple structure, quick opening/closing action, and low flow resistance.
Core Valve Components
- Valve Body: The main pressure-bearing component of the valve, usually manufactured by casting or forging with flanged ends. Common materials include ductile iron, stainless steel, aluminum bronze, duplex stainless steel, and alloy steel.
- Valve Disc: A critical component in direct contact with the medium, requiring careful material selection. Its thickness directly affects the valve's flow resistance and pressure rating.
- Valve Stem: One of the pressure-bearing components connecting the disc and valve body, and the only transmission part. Its upper end is connected to actuators such as handwheels, worm gear operators, pneumatic actuators, and electric actuators.
- Valve Seat: The key to the butterfly valve's sealing performance, a seal installed on the valve body or around the disc.
- (1) Soft-seated flanged butterfly valve: Primarily made of elastic materials such as rubber or PTFE.
- (2) Hard-seated flanged butterfly valve: Mainly constructed from metal, capable of withstanding high temperatures and pressures.
Figure 1: Exploded view of flanged butterfly valve core components
Main Types
- Centerline Flanged Butterfly Valve
- The valve stem axis, disc center, and pipeline center are collinear.
- Simple structure and low cost.
- Sealing is mainly elastic.
- Used in low-pressure, normal-temperature applications with no harsh requirements, such as water supply and heating systems.
- Double Eccentric Flanged Butterfly Valve
- The valve stem is offset from the centerline of the sealing surface, as well as from the pipeline and valve centerlines.
- Effectively reduces wear between the valve seat and seal ring.
- Sealing materials remain elastic, such as EPDM and PTFE.
- Commonly used in power generation, water supply, and metallurgy industries.
- Triple Eccentric Flanged Butterfly Valve
- The valve stem is offset from the sealing surface centerline, pipeline and valve centerlines, and the conical center of the valve sealing surface is offset from the pipeline and valve centerlines.
- Features all-metal sealing and multi-level sealing.
- Pressure and temperature ratings depend on the body material.
- Applied in high-temperature and high-pressure industrial fields.
Figure 2: Ductile iron double eccentric flanged butterfly valves
Disadvantages
The main disadvantages of flanged butterfly valves include unstable flow, cavitation, and vibration at low opening angles. Even when fully open, the disc partially obstructs fluid flow. Soft-seated butterfly valves are primarily limited by temperature and pressure constraints.
Main Standards and Specifications
| Category | Relevant Standards |
|---|---|
| Design and Manufacturing | EN593, API 609, ASME B16.34, GB/T 12238, ISO 10631 |
| Mounting Flange Standard | ISO 5211 |
| Flange Connection | ASME B16.5, ASME B16.47, GB/T 9113, EN 1092-1, AS 2129, AWWA C207, MSS SP44, BS 10, JIS B2212 |
| Face-to-Face Dimension Standard | EN558, ASME B16.10, API 609, GB/T 12221 |
| Pressure Testing | API 598, EN 12266-1, ISO 5208, GB/T 13927 |
| Fire Testing | API 607, API 6FA |
Typical Application Scenarios
- Water Treatment/Municipal Engineering: Water supply and drainage, fire protection, tap water, and sewage treatment systems.
- Heating, Ventilation, and Air Conditioning (HVAC): Cooling water and chilled water systems.
- Power Industry: Cooling circulating water, ash handling, and flue gas desulfurization systems (double/triple eccentric metal-seated butterfly valves).
- Petrochemical Industry: Process pipelines, oil product, and chemical transportation (primarily triple eccentric metal hard-seated butterfly valves).
- Shipbuilding: Seawater, ballast water, and fuel oil systems.
- Metallurgical Industry: Coal gas, combustion air, and dust removal systems.
Medium Types
- Conventional Media: Freshwater, seawater, sewage, drinking water, air, steam, food, pharmaceuticals, oil products, and weakly corrosive media such as oils, acids, alkalis, and salts.
- Low-Temperature Media: Liquefied Natural Gas (LNG), liquid oxygen, liquid hydrogen, ammonia, argon, liquid carbon dioxide, and liquid ethylene.
- High-Temperature Media: High-temperature air, hot flue gas, high-temperature steam, molten salt, and catalytic cracking oil and gas.
Figure 3: Stainless steel three eccentric flanged butterfly valves
Selection Considerations
The selection of flanged butterfly valves is a crucial part of practical procurement. Assessing factors such as medium type, temperature, pressure, operating environment, and budget to choose the appropriate flanged butterfly valve and actuation method is key to ensuring long-term stable operation.