Butterfly valves allow high flows
Butterfly Valves allow high flows with relatively low pressure loss from the valves, and
are typically used for flow control for valve openings from 30 to 70 degrees of full open. At
valve openings greater than 70 degrees, the pressure loss of a butterfly valve is too low to
produce any significant effect on flow or the energy loss of a flow system. Two special
applications for a butterfly valve include the use of a valve for free discharge and the use of a
butterfly valve for flashing or choking cavitation service. Free discharge typically produces high
pipe velocities at moderate pressure drops, and choking cavitation typically produces high
velocities with large pressure drops. The following paper also includes a review of flow
coefficients and the application of non-line sized valves, or valves installed in larger diameter
pipes with the aid of pipe reducers.
A third category of Butterfly Valve, the high performance butterfly valve, is occasionally
utilized in water treatment and distribution applications. These valves are characterized by
higher pressure and/or temperature ratings, different disc seating/sealing technology, and
premium materials. These valves frequently follow the design guidelines outlined in MSS SP-
68. The primary distinguishing design feature is a stem which is offset from the centerline of the
pipe. This offset design generates a camming action which allows for different types of seating
technologies when compared to resilient seated valves. These alternate seating technologies
frequently incorporate advanced seal materials, such as PTFE, RTFE, and other advanced
polymers which help the valve achieve higher pressure and temperature ratings. A high
performance butterfly valve is therefore a butterfly valve which has extended the performance
boundaries (in terms of pressure, temperature, and/or corrosion resistance) of traditional butterfly
valves.
