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.
