It is a fan in which air flows in a radial or perpendicular direction directly relative to the fan shaft . It also included the fan wheel, wheel, fan housing, drive mechanism, and inlet or outlet dampers. The fan wheel consists of fan blades mounted on a hub, which is turned on a shaft that passes through the fan housing. Air enters the fan through the center of the fan wheel, then turns 90° to pass over the fan blades and exit the fan housing. -forward or backward curved blowers, lld fan, i.dfd fans