Butterfly Valves are a type of quarter-turn valve that feature a pivoting disk mounted on a valve stem that can rotate within the valve body. By changing the position of the disk, control of the flow of fluid through the valve can be achieved. The valve stem can be rotated through a full 90o from the open to the closed position, which can be accomplished either manually using a handle or in an automated manner with a quarter-turn valve actuator.
There are several different ways to characterize butterfly valves – by body style, by materials used, and by disk alignment. This leads to some degree of overlap as these types are not all mutually exclusive.
The primary types of butterfly valves include:
Wafer style butterfly valves
Lug style butterfly valves
Flanged butterfly valves
Welded butterfly valves
Lined butterfly valves
Metal butterfly valves
Zero offset butterfly valves
Double offset butterfly valves
Triple offset butterfly valves
Flanged butterfly valves feature separate flanges the ends of the butterfly valve. The options for this type of butterfly valve include mono-flanged designs or double flanged designs. In many cases, the flanges are drilled and tapped to meet ASME standards for pipelines, or in some cases may be available undrilled.
Metal butterfly valves are intended for use in high pressure and high-temperature applications, and feature metal seat components that can withstand the pressures and temperature conditions as opposed to softer resilient seats or PTFE seats that might otherwise be compromised in those operating conditions. They also have metal valve bodies and full metal components as opposed to other design types such as plastic butterfly valves and are used for applications requiring fire resistance.
Wafer style butterfly valves are a design that has the valve control elements ready to be sandwiched between two flanges that, when installed, hold the water control valve in place. They are generally easier to machine than other types of butterfly valves, use less material, and are less expensive to produce. They are also very easy to install. Most butterfly valves are of wafer style, so the word “wafer” is often left off the description.
Since wafer style butterfly valves are installed between pipe flanges using a bolt and nut, it is impossible to disconnect just one side of the piping system from the valve. As a result, maintenance on wafer style butterfly valves usually requires a system shutdown. Wafer style butterfly valves, when installed, do not result in the transferring of the piping system weight through the valve body.
Butterfly valves have several advantages worth noting:
They are good for starting, stopping, and regulating the flow
They are available in a wide range of sizes, including large sizes, unlike some other types of valves
They are good for use with slurries and liquids that have suspended solids due to the large valve opening
Many of the designs are simpler and use less material, making them lightweight options
They are narrow and take up less space in an installed setting, and are easy to install, saving time and installation costs
They can be less expensive to purchase and are easier to maintain, thereby resulting in lower maintenance costs
They are fast-acting, being quarter-turn valves, and can open and close in less time than some other valve designs
They generate small pressure drops
With suitable seats, they can be used with chemicals and corrosive media
There are a few disadvantages associated with butterfly valves, however. One of the biggest is that by their nature, the disk is always in the flow path unlike ball valves, which have no obstruction to flow in the open position. There is, therefore, a possibility that cavitation and choke can occur, and that the movement of the disk may be impacted by flow turbulence.
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