| 摘要 |
A generally cylindrical hub with a vertical axis has a bottom and a top and a side wall. The side wall has a plurality of circumferentially spaced radial extending minor cavities. The top has an axial aperture forming a major cavity. A vertically extending hollow cylindrical tube has a lower end received by and supported by the axial aperture. A plurality of generally cylindrical hollow arms extend radially in a common horizontal plane. Each cylindrical arm has a closed exterior end and an interior end received by and supported by an associated radial minor cavity. Each cylindrical arm has a plurality of rows of perforations for the flow of a fluid through the cylindrical tube, the hub, the arms and the rows of perforations.
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