| 摘要 |
PURPOSE:To prevent the freezing of a steel cover in the winter season as well as retain even heat of valves in the cover by a method in which plural holes are drilled from below to above in the receiving frame of the steel cover, and heaters and thermostats are inserted into the holes and connected to a power source through a connecting box. CONSTITUTION:A connecting box 13 is provided in the receiving frame 12 of a steel cover 10. In the connecting box 13, a wire 15 is extended through a hole 14 drilled in the receiving frame 12 into the ground and connected to a power source. On the other hand, plural holes 16 are drilled from below to above in the inside of the receiving frame 12, and cylindrical heaters 17 or thermostats 18 are inserted into the holes 16 from below and connected to the connecting box 13. The freezing of the steel cover in the winter season can thus be prevented, and also even valves in the steel cover can be kept warm. |
