In summary, the main concerns when selecting a fan are: noise, air flow (CFM), static pressure, physical size, bearing type, motor type, motor protection and life expectancy. Noise from axial fans is usually caused by aerodynamic forces such as: uniform inlet flow, non-uniform inlet flow, rotor-casing, impulsive, non-uniform rotor geometry and unsteady flow field. Qualtek offers four main types of bearings in the axial fans: one ball – one sleeve, two ball, sleeve, and hydro dynamic. Two types of AC motors are used in Qualtek’s AC axial fans; shaded pole and permanent split capacitor. DC brushless motors run cooler than AC motors, have more precise control, and higher torque levels. The DC motor typically operates within an efficiency range of 85%-90%, compared with 20% to 40% for the shaded pole and 50% to 70% for the PSC AC motors. Also offered are three types of motor protection: thermal, impedance, and integrated circuit. Thermal protection uses a thermal relay inside the motor to break the circuit to the winding coil without causing damage and is primarily used in larger fans. Impedance protection is a passive form of protection which raises the impedance of the motor windings to suppress increases in current and keep the motor temperature from rising above a preset level. It is used mainly in fans 120 mm in diameter or smaller. Qualtek brushless DC fans are available with IC motor protection which shut down the motor for a period of time when a lock is detected. For more information about AC and DC axial fans please visit our website at www.Qualtekusa.com.