Butterfly valves are used for isolating or regulating flow. They are a quarter turn valve similar to a ball valve except the closing mechanism is a disk instead of a ball. Butterfly valves are typically lower in cost to other valve types as they are lighter in weight meaning less support is required to have them in line. The disc of the valve is operated by either a lever, gear or actuator. When the valve is closed the disc blocks the flow- when open the disk turns to allow flow to pass through; however the disk will always be present within the flow resulting in a pressure drop regardless of valve position. Butterfly valves can also be open incrementally to throttle flow.
- Wafer Style or Lug Style – typical
- Designed to maintain a seal against bi-directional pressure differential to prevent backflow in systems designed for unidirectional flow
- Accomplishes this with a tightly fitting seal, i.e., gasket, o-ring, precision machined, and a flat valve face on the upstream and downstream sides of the valve
- A lug-style butterfly valve used in dead end service generally has a reduced pressure rating
- For example, a lug-style butterfly valve mounted between two flanges has a 150 psi pressure rating.
- The same valve mounted with one flange, in dead end service, has a 75 psi rating
- Flanged – it is not uncommon to see a flanged butterfly valve in high performance applications
- Have threaded inserts at both sides of the valve body
- Allows Flange Butterfly Valve to be installed in a system using two sets of bolts and no nuts
- Installed between two flanges using a separate set of bolts for each flange
- This setup permits either side of the piping system to be disconnected without disturbing the other side
- Concentric Butterfly Valve
- Has a resilient rubber seat with a metal disc.
- Double Eccentric Butterfly Valve – also known as a High Performance Butterfly Valves or Double Offset Butterfly Valve
- Different type of materials are used for the seat and disc.
- Triple Eccentric Butterfly Valve – also known as Triple Offset Butterfly Valve
- Seats are either laminated or a solid metal seat design
- Design prevents gulling and scratches between the metal seat and the metal disc due to its unique construction
- Only time the seal comes into contact with the seat is at the point of complete closure
- Generally used in applications which require bi-directional tight shut-off in Oil & Gas, LNG/NPG terminal and tanks and Chemical Factories
- Widely use for dirty/ heavy oil to prevent extrusion.