Abstract: An air jet cleaning apparatus for use with throttling devices mounted in ventilation ducts in which the throttling device includes a body having opposite air inlet and outlet sides and a plurality of fine through passages for conveying air flowing from the inlet to the outlet sides thereof. The apparatus includes a deflector shield mounted adjacent the inlet side of the body to allow for relative movement between the deflector and the body. The shield has an opening facing the inlet side of the body which is caused to sweep over the inlet side during relative movement between the shield and body. A duct provides communication between the shield and the outlet side of the throttling device whereby the drop of pressure across the throttling device diverts a partial air flow through the shield in another direction than the main air flow into the body of the throttling device in order to clean the surface of the inlet side of the body.