| 摘要 |
A manhole cover is provided to offer high reliability by operating normally regardless of seasons by not being clogged by soil, sand or various filth, to prevent malfunction by having a simple structure and to reduce the manufacturing cost. A manhole cover, for covering a manhole having an inside space and controlling pressure inside a manhole by operating when the pressure inside a manhole rises, includes a cover body(32) covering the manhole and having many through holes(32b), a head(34a) mounted to the cover body to be reciprocated and descent by dead weight to seal up the through hole tightly and ascent to open the through hole when the pressure inside the manhole rises, an extension(34b) fixed to the lower part of the head and extended downward to the inside of the manhole via the through hole, and a stopper installed to the bottom of the extension and limiting the upward movement of the head and the extension on the lower part of the cover body. |
