| 摘要 |
<p>Embodiments are described for preventing downward flow of substantial surface water into an underground ventilation duct communicating upwardly to a ground surface opening. The embodiments comprise a support having a top opening and an opening in a lower portion above a floor. The opening in the lower portion is for venting communication with a proximate portion of the ventilation duct. The support supports at least one seat and paired buoyant gate set. The seat is mounted perpendicularly relative to the gate and a portion of a passageway under the seat for fluidly communicating beyond such portion to the top opening of the support and to the proximate portion of the ventilation duct. The buoyant gate is positioned lower than the seat and the passageway, is of sufficient size to block the passageway, and is responsive to water rising in the support by floatingly pivoting upwardly until engaging the seat, thereby blocking the passageway. In an embodiment, the seat of at least one set is mounted under the top opening spaced from one of the opposing sides a horizontal distance nominally equal to a fraction applied to a length for the particular opening, the fraction having the numerator 1 and a denominator which is the sum of 1 plus the number of seat and gate sets, and the buoyant gate has a seat engagement height nominally equal to the same fraction applied to the same opening length.</p> |
