| 摘要 |
PROBLEM TO BE SOLVED: To effectively discharge gas through a safety valve.SOLUTION: A lid 68 has a safety valve 70. In the safety valve 70, a first recess 76 is formed on an inner side of the lid 68, and a second recess 78 is formed on an outer side of the lid 68 corresponding to the first recess 76 of the lid 68. The safety valve 70 is formed between the first recess 76 and the second recess 78. According to the present invention, cross sectional areas of the first recess 76 and the second recess 78 on a cross section vertical to a plane direction of the lid 68 get gradually smaller toward the safety valve 70. Therefore, a pressure of gas flowing to the safety valve 70 from an inner side of the lid 68 is gradually increased when passing through the first recess 76, and a pressure of gas flowing to an outer side of the lid 68 from the safety valve 70 is gradually decreased when passing through the second recess 78. Thus, pressure reduction when the gas passing through the first recess 76 is emitted to the outer side of the lid 68 can be restrained, so as to effectively exhaust the gas. |
