| 摘要 |
<p>A valve closure mechanism having a moveable plate (28) that is displaceable relative to at least one fixed plate (26, 27), each of the plates having perforations (30, 31) that are mutually offset between one plate and another, so that in an open position of the valve the perforations in each plate allow air to pass therethrough and in a closed position of the valve the moveable plate makes abutting contact with the at least one fixed plate such that at least some of the perforations in each plate are sealed by the plate complementary thereto.</p> |
