Abstract: A butterfly valve plate is provided for use in a pneumatic surge valve or the like, wherein the valve plate is designed for reduced noise with increased mass flow capacity. The valve plate is of the type having an offset stem hub for supporting the valve plate on a pivot stem or shaft for movement between closed and open positions within a flow conduit. A pair of part-circular and generally axially extending acoustic fences are carried respectively at opposite sides of the valve plate in peripheral positions for flow-through passage of air when the valve plate is opened. An enlarged and smoothly contoured noise reduction collar is formed on the stem hub at the downstream side of the valve plate, generally at the periphery thereof to substantially fill and occupy the space between the stem hub and the adjacent end of the downstream-side acoustic fence.

Abstract: A method and apparatus for eliminating vortex whistle noise in a radial-to-axial compressor intake uses a plurality of vortex-disturbing tabs mounted to the trailing edges of inlet guide vanes and extending into the flow path between adjacent vanes. The tabs are mounted to the guide vane so that the tab is always perpendicular to the guide vane, regardless of the vanes angular position.