| 摘要 |
PROBLEM TO BE SOLVED: To provide a valve box and a steam seal having the same fire resistance as the specification thereof. SOLUTION: A stem seal 2 consists of a cylindrical seal membrane 6 for sealing a stem, and a membrane supporting flange 7. The seal membrane 6 has a wave profile for demarcating one more loop shaped passages 11a to 11c whose boundary is connected to contact surfaces 13a to 13d in a radial direction inner surface. Each passage is inclined at 5 deg. to 10 deg. in relation to a vertical flat surface in the longitudinal direction axial line of the seal membrane 6. In the loop shaped passage, a labyrinth seal is formed to prevent leakage of a fluid along the outer surface of the stem. A supporting bearing 8 for the stem is arranged on the membrane supporting flange.
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