The Helios RR 315 centrifugal tube fan is designed for direct installation in the duct system. It is suitable for conveying medium and small air volumes against high resistance. The housing is made of galvanised sheet steel with round connection pieces that are adapted to standard ducts. The radial impeller has backward curved blades made of galvanised sheet steel, which are pressed directly onto the motor and dynamically balanced as a unit. It operates with a low noise level and high efficiency. The fan contains a single-phase AC external rotor motor with a closed design, maintenance-free, integrated thermal contacts, sealed and with low-noise, long-term lubricated ball bearings. The power can be controlled by an electronic controller or a step transformer.