[tsuter]

If you hold it in your hand and look in the side that has the metal hose attached i.e., air flow would be towards you see arrow on top, then the metal gate slides left to right across the hole to block it. It is activated by the bmetallic strip which is mountd inside the elangated portion and fixed by a metal plug at the end. Since this strip flexes left to right, that is the movement of the gate in the slot.