| 摘要 |
<p>A control knob (2) has steering contact externally on valve hood (1) of a slot valve. Inclined grooves (9) in an internal void (8) will in case of movement of said control knob in one or the other direction cause a tightening member (7) to move and in turn cause damper (6) of the slot valve to open or close the valve slot in a window frame.</p> |
