At least one loop of absorption blind hole is evenly distributed around the segmental concave cavity along the radial direction of plane. 径向面上沿圆缺凹腔周围均匀分布不少于一圈的吸收盲孔;
The axial lower section of the hemisphere case is equipped with the absorption cavity which connects with the segmental concave cavity. 半球壳体轴向下部设有连通圆缺凹腔的吸收腔。