A backdraft shutter is used with inline fans and duct, to stop air flowing in the “back” direction. They have a single disk flap on two hinges.
Backdraft Shutter – Metal – 200mm
$38.00
A backdraft shutter is used with inline fans and duct, to stop air flowing in the “back” direction. It has “butterfly” wings and a very weak spring to minimise airflow reduction.
Eugene Legat –
They supplied the item I required and I purchased it.