Butterfly valve. Valves and are generally made of plastic or steel, the latter being the most widely used in chemical and petrochemical applications. Steel grades range from the most common type, namely carbon steel, with standard stainless steel being the second most common. Stainless steel alloys, which include nickel or copper are used in applications that require higher corrosion or heat resistance. In such cases, the most commonly used valve configurations -- ball valves, gate valves, check valves, globe valves and butterfly valves -- are often forged or cast as duplex valves, super duplex valves, alloy 20 valves, monel valves, inconel valves, incoloy valves and 254 SMO valves (6Mo valves). Titanium valves are also used in some highly corrosive applications. Titanium is not a stainless steel alloy.
Design Details: A butterfly valve is a valve which can be used for
isolating or regulating flow. The closing mechanism takes the form of a
disk. Operation is similar to that of a ball valve (quarter turn) which
allows for quick shut off. Butterfly valves are generally favoured
because they are lower in cost to other valve designs as well as being
lighter in weight, meaning less support is required. The disc is
positioned in the centre of the pipe, passing through the disc is a rod
connected to an actuator on the outside of the valve. Rotating the
actuator turns the disc either parallel or perpendicular to the flow.
Unlike a ball valve, the disc is always present within the flow,
therefore a pressure drop is always induced in the flow, regardless of
valve position. The valve may also be opened incrementally to throttle
flow.
