Fan inlet rings are devices used to maximise the performance of fans, such as backward curved centrifugal fans, by guiding air into the impeller blade (the rotating part of a fan) inlet. Using a fan at peak efficiency minimises noise emitted and power consumption from the fan whilst delivering optimal performance.
Fan inlet rings ensure smooth laminar flow (flow in parallel layers, with no disruption between the layers) of air as it enters the impeller.
Fan inlet rings are usually positioned with the ring surrounding the inlet, and slightly overlapping into the interior. This helps to reduce noise induced by turbulence, eliminate flow disturbances before air is let into the fan and keep power consumption to a minimum for maximum efficiency.
Fan inlet rings also serve the critical purpose of blocking exhaust air from re-entering the air intake. Due to the frequent exposure to atmospheric moisture, fan inlet rings are usually made of materials that don't rust.