Patent attributes
A backflow prevention device includes at least one backflow prevention unit. The backflow prevention unit includes a frame, a first edge shutter plate, a second edge shutter plate and plural intermediate shutter plates. The frame includes an airflow channel. If the first inner sidewall is disposed over the second inner sidewall, the first edge shutter plate and the plural intermediate shutter plates are configured to open or close the airflow channel, and the slab of the second edge shutter plate is inactive. Whereas, if the second inner sidewall is disposed over the first inner sidewall, the second edge shutter plate and the plural intermediate shutter plates are configured to open or close the airflow channel, and the slab of the first edge shutter plate is inactive.
