The Helios Fans RVK 355 is a tightly sealing cover for both supply and extract air openings, designed especially for use with reversible fans. It features a spring-loaded mechanism for reliable automatic closure, preventing unwanted airflow when the fan is not operating. Constructed from high-strength, impact-resistant plastic in a light grey finish, the RVK 355 ensures long-term durability even in challenging environments. The stainless steel spring resists corrosion, and the number of louvres varies depending on the unit size. It supports a maximum supply air velocity of 6 m/s and exhaust air velocity of 8 m/s, making it suitable for a wide range of ventilation applications.