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Centrifugal Fan Components: Impeller, Housing, Drive Systems, and Duct Design

Centrifugal fans (squirrel-cage blowers) move air/gas continuously in industrial HVAC, material handling, combustion, and pollution control. Understanding core components ensures proper selection and maintenance.

Impeller

Rotating hub with mounted blades. Air enters axially, accelerates radially via centrifugal force, discharges 90° from intake. Configurations:

Forward-curved: High volume, low pressure, quiet. Clean air only.
Backward-curved: High efficiency, non-overloading power curve. General purpose.
Radial: Rugged, handles particulates. Lower efficiency.
Airfoil: Highest efficiency, clean air.

Double-inlet and multi-stage (series-mounted) impellers for high-pressure/large-volume demands.

Fan Blades

Blade geometry dictates performance curve. Match blade type to system resistance (static pressure) and required flow (CFM). Wrong selection = energy waste, noise, surge/stall.

Fan Housing (Scroll)

Converts velocity pressure to static pressure. Optimized volute shape minimizes turbulence, noise, and power loss. Must withstand centrifugal loads at operating speed.

Drive Shaft & Mechanisms

Direct drive: Shaft = motor shaft. Speed fixed by motor RPM. Simple, no belt loss.
Belt drive: Sheaves on motor and fan shafts. Fixed ratio unless belts slip. Allows speed selection via sheave sizing.
Variable speed: VFD (variable frequency drive) or mechanical variable drive. Precise airflow control, energy savings at part load.

Shaft sized for impeller weight + dynamic loads + safety factor.

Inlet/Outlet Ducts

Straight, gradual transitions. Sharp elbows, undersized ducts, or restricted inlets cause flow distortion, noise, and performance drop. Duct design is as critical as fan selection.