"NON-RETURN DAMPER" . "Recorded" . "mvsen" . "mvsen" . "RDS" . "BACK FLOW DAMPER" . "In a multi fan installation a non-return damper prevents back draught through the non-operating fans." . "NON-RETURN DAMPER" . "RDS1048796831" . . "A gas flow damper that prevents back flow in a duct." . "2009.03.04" .