This model is a round backdraft (or intake) damper designed to prevent cold air from flowing back into warm air ducts, e.g. a bathroom extractor fan. It allows airflow in one direction while blocking reverse airflow.

The model has a cylindrical frame with an hinged flap valve. When air flows through the duct in the intended direction, the flaps open freely to allow air to pass. As soon as the airflow stops or reverses, the flaps swing shut to seal off the duct.

Key features:

• Cylindrical frame with outer diameter of 10cm to fit standard ductwork
• Frame thickness of 1mm
• Flap attached to the frame with small hinges along the top edge
• 15% infill recommended for print
• No support needed
• Standard 0.20mm layer height
• Printed in ABS, but PLA should be fine too

This round backdraft damper insert can be inserted into ductwork to prevent reverse airflow efficiently while allowing normal airflow to pass through with minimal restriction.

Trim the hinges to the right length so that the frame fits the duct, but still allows the flap to move freely. Some glue might be required to keep the top cover attached. I also used glue to attach some extra insulation to the flap.

The model can be edited on onshape using the variables tables here