A quarter-turn rotational motion valve that is used to stop, regulate and start flow is the butterfly valve. It is easy and fast to open and a 90-degree rotation of the handle provides a complete closure or opening of the valve. In large butterfly valves comes equipped with a gearbox in which the handwheel by gears is connected to the stem. At the expense of speed, the operation of the valve gets simplified.
Butterfly valves have a short circular body, a round disc, metal-to-metal or soft seats, top and bottom shaft bearings, and a stuffing box. There are various variations in the construction of a butterfly valve. A commonly used design is the wafer type which fits between two flanges. Another type is the lug wafer design which is held in place between two flanges by bolts that join the two flanges and pass through the holes in the valve’s outer casing. Butterfly valves are also available with flanged, threaded and butt welding ends, but they are not used often.
Especially for large valve applications, butterfly valves possess many advantages over gate, globe, plug, and ball valves. It’s most obvious advantages are a reduction in weight, usage of space and cost. The maintenance costs are usually low because there are a minimal number of moving parts and there are no pockets to trap fluids. These valves are specifically built for the handling of large flows of liquids or gases at relatively low pressure and for the handling of slurries or liquids with large amounts of suspended solids. The valves are built on the principle of a pipe damper. The flow control element is a disk of approximately the same diameter as the inside diameter of the adjoining pipe, which rotates on either a vertical or horizontal axis. The valve is fully opened when the disk lies parallel to the piping run. When the disk approaches the perpendicular position, the valve is shut. Intermediate positions, for throttling purposes, can be secured in place by handle-locking devices.
Typical applications of Butterfly valves
A Butterfly valve can be used in many different fluid services and they perform well in slurry applications. The following are some typical applications of Butterfly valves:
Advantages of Butterfly valves