What Is a Butterfly Valve?
A butterfly valve is a quarter-turn valve used to shut off, throttle and regulate the flow of liquids, gases, steam and granular or viscous media. A circular disc, the butterfly, is mounted on a shaft in the centre of the flow path. Thanks to its simple construction, low weight and small installation length, it is one of the most frequently used valve types in industry.
Butterfly valves open and close very quickly, provide bidirectional sealing with low pressure loss and can easily be combined with gearboxes and actuators for automated operation.
Working Principle
The operation of a butterfly valve depends entirely on a quarter-turn rotation of the disc. When the disc is turned perpendicular to the flow, it closes the bore and stops the medium. When it is turned parallel to the flow, the valve is open and the fluid passes around the disc. Intermediate positions allow the flow rate to be regulated. Because the disc remains in the flow path even when fully open, it causes a small pressure drop. Flow through a butterfly valve can be in either direction.
Butterfly Valve Types
- Wafer type: clamped between two pipe flanges; lightweight and economical, with bidirectional sealing. It is not recommended as an end-of-line valve.
- Lug type: each flange is bolted to threaded lugs on the body, so the valve can be used at the end of a line and downstream piping can be removed without shutting down the system.
- Double flanged: suited to both low and high temperatures, preferred for clean, neutral media.
- Stainless steel: resists corrosion and is an economical solution for lines carrying chemical media.
- Actuated: fitted with an electric, pneumatic or hydraulic actuator for automatic opening and closing; electric actuators can also be operated manually during power outages.
- Hydraulic: operated by a hydraulic power unit and able to close automatically in abnormal line conditions.
- High-performance (HP): designed for temperatures and pressures beyond the limits of standard butterfly valves, common in chemical and oil applications.
Technical Range
Luna Flow Control supplies butterfly valves in steel, stainless steel, bronze, aluminium, plastic and other materials, with flanged, SW/BW or threaded connections. The range covers DN 50 to DN 1200, PN 6 – 63 and operating temperatures from -50 °C to +560 °C, with lever, gearbox, electric, pneumatic or hydraulic actuation.
Application Areas
- Hot and cold water installations
- Water treatment and distribution
- Chemical and oil industries
- Gas and compressed air lines
- Lines carrying slurries or particulate media
Advantages
- Small footprint and low weight
- Tight shut-off with bidirectional sealing
- Simple, fast operation
- Suitable for high temperatures
- The operating mechanism does not contact the medium, preventing scale build-up
- Maintenance possible without removing the valve from the line
Selection and Maintenance
Select the body, disc and seat materials according to the medium and temperature, and choose the connection type (wafer, lug or double flanged) according to the installation position. Regular inspection of the seat and shaft seals ensures reliable operation of the valve for many years.
