A 6" Jamesbury controlled butterfly valve installed in a 8" line supplying water to a tank. The line has conc. reducers on the inlet and outlet of the valve. The valve shaft is mounted horizontally. We are having wall failures on the bottom of the outlet conc. reducer due to cavitation caused by the valve. The system operates at 30 psi and a flow rate of approx 640k/hr. The valve usually opens only about 25%. The open side of the disk directs the water flow to the area of failure, but it is not erosion.Pictures indicate the roughness of cavitation, not the smoothness of erosion. The pipe system is carbon steel, A-106 & A-234 for the components. Jamesbury has an excellent valve sizing manual that covers your case. Nobody "likes" butterfly valves as such, but they can be made to work and work surprisingly well. There are ways to deal with the cavitation issue without extreme modification of you piping, but you'll have to sort out the specifics with your valve rep. BobPE raised a good point about controllability of a conventional disk. A characterized disk is certainly better suited for control.

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