How the 4 Inch Back Draught Damper Seals an Idle Duct
This is a one-way gate in the duct. Spring-loaded aluminium flaps lift when the fan pushes air and drop shut when it stops, with a rubber seal closing the gap at rest. The housing is galvanized sheet steel. On a 4 in run it weighs half a pound and adds about 3.5 in of depth.
Mounting a Backdraft Shutter in the Right Place
It mounts horizontally or vertically, which is unusual for a gravity damper and comes from the spring rather than relying on weight. Fit it downstream of the fan with the flaps opening in the direction of flow. Understand the cost: flaps sitting in the airstream take a small bite out of static pressure, and on a small fan that is not nothing. Keep the seat clean, because dust on the rubber is what stops a damper closing fully. On a small run the flaps are light enough to open at low fan speed without stalling.
Key Features
- Spring-Loaded Aluminium Flaps: Open on airflow and close under spring pressure, with nothing to power.
- Rubber Seal: Closes the gap at the seat so a stopped duct actually stays shut.
- Galvanized Steel Housing: Corrosion-resistant in the damp air an exhaust run carries.
- Horizontal or Vertical Mounting: Spring loading means it does not depend on gravity to close.
- 4 in Duct Fit: Matches Ruck 4 in components and standard 4 in ducting.
- Fully Mechanical: No wiring, no actuator and no control signal to lose.
Technical Specifications
| Specification | Value |
|---|---|
| Duct Size | 4 in |
| Housing | Galvanized sheet steel |
| Flaps | Spring-loaded aluminium |
| Seal | Rubber |
| Mounting | Horizontal or vertical |
| Operation | Airflow-opened, spring-closed |